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Freshwater resources are scarce globally, and the increase in carbon dioxide (CO 2) concentration leads to both a decrease in soil moisture and arid climate, further limiting agricultural production. Therefore, it is critical to achieve water efficiency in agriculture under elevated CO 2 concentration. A comprehensive analysis was conducted on the research topic of efficient agricultural water under elevated CO 2 concentration using bibliometric methods. The results show that the number of papers on this research has changed from an accumulation phase (1992–2005, 395) to a growth phase (2006–2023, 963). "Carbon dioxide", "water-stress", "growth", "photosynthesis", "yield", and other keywords have been the focus of past research in this area. Kimball BA and Ainsworth EA are the most influential authors in this area. Leakey's (2009) paper in "Experimental Botany" was the most contributing study, summarizing six lessons about the effects of CO 2 enrichment on the relationship among carbon, nitrogen, and water in plants. The United States and China were the most influential countries. Over time, research has shifted from an early focus on atmospheric CO 2 change itself to the response of crops to elevated CO 2 in agricultural production. The efficient crop production strategy under the interaction of environmental factors is becoming a hot spot for future research, and the emission and use of greenhouse gases, the improvement of crop quality, and the efficient guidance of models are also worth exploring. Overall, this study presents a quantitative analysis and comprehensive review of past research conducted on the effect of water and fertilizer on agricultural production under CO 2 enrichment. It also offers suggestions and expectations for future research on the hot spot direction of efficient crop production under climate change. • The continuous research attention is closely related to climate change caused by CO 2 enrichment. • The main research fields included CO 2 enrichment, water stress, crop growth and photosynthesis. • The co-citation analysis reveals broad research clusters in the literature. • The new research focus will be interactive climatic factors, greenhouse gas recycling, and modeling. [ABSTRACT FROM AUTHOR]

This paper highlights the evolution and impact of the SWAP model (Soil – Water – Atmosphere – Plant), which was initiated by R.A. Feddes and colleagues fifty years ago, in 1974. Since then, the SWAP model has played a crucial role in the advancement of agrohydrology. This paper highlights some major advances that have been made, especially focussing on the last fifteen years. The domain of the SWAP model deals with the simulation of the soil water balance in both unsaturated and saturated conditions. The model solves the Richards equation using the water retention and hydraulic conductivity functions as described by the Van Genuchten – Mualem equations. Bimodal extensions of the Van Genuchten - Mualem relationships have been implemented, as well as modifications near saturation and addressing hysteresis. An important sink term in the Richards equation is root water uptake. Crop development plays an important role in a robust simulation of root water uptake. That is why a link has been made with the dynamic crop growth model WOFOST. Instead of using a prescribed crop development, a distinction between potential and actual crop development is calculated by reducing the potential photosynthesis as a result of water or oxygen stress. Since the early days of SWAP, empirical and macroscopic concepts have been used to simulate root water uptake. Recently two process-based concepts of root water uptake and oxygen stress have also been implemented. Another important sink-source term in the Richards equation is the interaction with artificial drains. In SWAP, drainage can be simulated by either using prescribed or simulated drain heads and simulation of controlled drainage with subirrigation is possible. Finally, we briefly elaborate on three studies using SWAP: water stresses in agriculture in the Netherlands, regional water productivity in China, and controlled drainage with subirrigation. We finish discussing promising developments for the near future. • Advances in soil-vegetation-atmosphere transfer modelling in the SWAP model. • Coupling of soil water dynamics with dynamic crop growth model. • Process-based root water uptake and oxygen uptake functions. • Climate-adaptive drainage with subirrigation. [ABSTRACT FROM AUTHOR]

Alfalfa (Medicago sativa L.) is a high-water-use crop primarily cultivated in water-scarce areas in China. Deficit irrigation is still considered a promising strategy to improve regional water productivity (WP) despite the risk of yield loss. The objectives of this paper were to better understand the effects of deficit irrigation on alfalfa yield and WP via a meta-analysis, to quantify the relationship between alfalfa yield and crop water use and to identify water management practices that strike a balance between costs and returns in China. A total of 28 published papers covering 26 locations showed that deficit irrigation reduced alfalfa yields by 17.4% ± 1.2% and increased WP levels by 14% ± 2.5% relative to full irrigation. The yield and WP changes were significantly (P < 0.05) caused by the irrigation application rate and timing, soil texture, soil field capacity and soil organic matter. The application of deficit irrigation only at the budding stage effectively reduced alfalfa yield losses, with the lowest yield loss (8%) relative to full irrigation during the whole growth stage. In soil with a high bulk density (1.5–1.6 g cm−3), high organic matter content (>30 g kg−1) and sandy loam soils, the magnitudes of the effects on yield reduction were smaller than those on WP improvement. Both alfalfa biomass yield and WP exhibited a parabolic relationship with the crop water use. Based on an economic and trade-off analysis, a deficit level of 90% of full irrigation is recommended in semi-humid regions for WP maximization. Deficit levels of 80% of full irrigation and 60% of full irrigation are more appropriate in semi-arid and arid regions, respectively to maximize the net income per unit water. • Effects of deficit irrigation on alfalfa production was analyzed by meta-analysis. • Deficit irrigation reduced alfalfa yields by 17% versus full irrigation. • Deficit irrigation increased water productivity by 14% versus full irrigation. • Deficit irrigation only at the budding stage reduced alfalfa yield losses. [ABSTRACT FROM AUTHOR]

The water-use rights trading system fully embodies a new concept of water resources management of the 'water saving priority' and market-oriented governance. The price mechanism is a core component of this system, and the benchmark price is its cornerstone. Accordingly, this paper analyzes the connotation and characteristics of the water-use rights benchmark price (WURBP). Based on the Marxist labor theory of value and land rent theory, it is proposed that the WURBP should be the economic embodiment of the water-use rights value. Considering the case of the Ningxia Yellow River irrigated area, a WURBP calculation model was established using the fuzzy comprehensive evaluation model to calculate the agricultural WURBP. The obstacle degree model was introduced to analyze the main factors affecting the WURBP. Results show that the WURBP for food crops in the Ningxia Yellow River irrigation area is 0.252 yuan/m3, and 0.652 yuan/m3 for cash crops. Water yield coefficient, runoff coefficient, per capita GDP, farmland irrigation utilization coefficient, and ecological water consumption have gradually become the primary obstacles affecting agricultural WURBP. Water administrative departments should adjust the WURBP according to the actual situation. This paper innovatively puts forward the concept of WURBP. These results have important practical significance for improving China's agricultural water-use rights trading price system. • Proposed the concept of water use rights benchmark price. • Using game theory combination weighting method to calculate weight. • Crops are divided into food and cash crops to calculate the WURBP. • The obstacle degree model is built to analyze the main factors affecting the WURBP. [ABSTRACT FROM AUTHOR]

There was presently a lack of multidimensional investigation on the impact of virtual water flow (VWF) on regional water use and scarcity. A framework for impact analysis of VWF in consideration of blue, green and grey water differentiation, taking the crop-water relationship estimation in 31 provinces of China as case study, was established in current paper. Results showed that, VWF, which mainly from northern to eastern plain and southeast, reduced agricultural water footprints by 8.3 (blue), 322.0 (green) and 52.5 (grey) G m3. National water stress index reduced from 1.20 (severe water stress) to 0.92 (high water stress), comparing crop consumption to production perspectives. VWF alleviated the resource-based water scarcity attributed to green water stress in south of the Yangtze River, and transformed the resource-based to systematic water scarcity in Xinjiang (XJ). Clarifying the influences of VWF on blue, green and grey water is the innovation of the analytical framework proposed in current paper. • Influences of virtual water flow (VWF) on blue, green and grey water footprint scarcity were quantified. • Green and grey VWFs and their effects on water resources were more impressive than blue water. • VWF alleviated water stress and changed water scarcity type in crop production of China. • Crop production improvement and optimization are proposed to increase the benefits of VWF. [ABSTRACT FROM AUTHOR]

Water rights trading volume (WRTV) is an integral part of an effective transaction. At present, in China, WRTV is mostly based on the water demand of the transferee, not the transferor. Some transactions last for a long time, yet lack proper measures to adjust trading volume, making theoretical and quantitative studies on WRTV necessary and essential. Therefore, based on the theory of property rights, this study first analyzed the concept of WRTV, and proposed that WRTV must consider the tradable water volume (TWV) of the transaction parties. For that, this paper divided water rights trading into two stages: initial stage and operation stage, to analyze how to measure WRTV in different stages. Second, currently, industry or sector is a major player of water rights trading. TWV of industry is, hence, the difference between the initial water rights volume (IWRV) and water demand of industry, significant for calculating WRTV in different stages. For that, this study employed the ratio method to calculate the IWRV of industry, and the Grey Model—GM (1,1) to predict the water demand of industry. Last, this paper carried out a case study on the inter-league and inter-city water rights trading between Bayannur city and Ordos city in Inner Mongolia, China. Results show that the TWV of industry of Bayannur and Ordos in 2030 are – 904.966 million m3 and − 87.135 million m3 respectively, implying insufficient TWV for the transferee, which may lead to transaction breakdown. The theory and calculation method of WRTV proposed in this study lay a theoretical foundation for WRTV measurement, and can help facilitate the orderly development of water rights trading in China. [Display omitted] • The volume of water rights should be considered the tradable water volume of the transaction subjects at the same time. • The impact of the change of the tradable water volume on the water rights transaction volume is analyzed. • The change of water rights trading volume has a great impact on trading, and even leads to the transaction rupture. • Forecasting the trading volume of water rights between Bayannur city and Ordos city in Inner Mongolia of China in 2030. [ABSTRACT FROM AUTHOR]

China's Yellow River Basin (YRB) has large watershed but scarce water resources. More importantly, most parts of the YRB are located in semi-arid areas of Northwest China, where the ecology and environments are fragile. So, ecological restoration and agricultural production always are the key research topics of the YRB. However, the specific research interest of YRB changed over time and was always closely related to the implementation of government policies. Hence, we conducted a comprehensive analysis of YRB's research topics based on the methods of bibliometrics. The results showed that the number of papers about YRB's research experienced a change from slowly increasing (1998–2010, 83 papers) to rapidly increasing (2011–2015, 128 papers), and then to exponentially rising (2016–2020, 369 papers). Secondly, the main research fields of the YRB included farming, crops, water, soil, environment, and etc. The journal of Agriculture Water Management had the highest global total citations and H-index, even local cited references were the highest among all of the reference papers about the YRB. Through summarizing the most cited papers and references, we found the most important research hotspots about the YRB were: the impacts of climate change and human activities on the amount of sediment in the YRB, the management of soil erosion and vegetation restoration in the YRB, and the relationship between crops and environment and management in the Loess Plateau of China. In addition, " Loess Plateau " was the most frequent keyword in the past ten years and the popularity of " climate change " rose sharply in the past five years. For YRB's research in near future, how to effectively control carbon emissions, greenhouse gas (GHG) emissions, and carbon surplus is becoming an important implication for YRB's agricultural production and ecological restoration in the future. In general, this research is expected to promote a comprehensive and quantitative understanding of the past, present and future of YRB's research. • The research of Yellow River Basin (YRB) has exponentially increase in 2016–2020. • The research interest was closely related to the implementation of government policies. • The main research fields of the YRB included farming, crops, water, soil, environment. • The keyword of "Loess Plateau" was the most frequent keyword in the past ten years. • The carbon emissions, and carbon surplus is becoming an important research direction for YRB. [ABSTRACT FROM AUTHOR]

Water use and efficiency assessment from crop production-consumption process provided a new perspective for regional agricultural water management. An evaluation framework of water use efficiency (WUE) coupling crop cultivation, commutation and consumption processes was established in this paper. The impact of virtual water flow on provincial irrigation water use efficiency, and its implications for irrigation management were assessed based on the inter-provincial virtual irrigation water flow (VIWF) estimation for cereals of China The results showed that national IWU, IWP and IE for cereal production in 2018 were 268.89 Gm³ , 1.815 m³ /kg and 0.494 respectively. Total VIWF among 31 provinces was calculated to be 85.25 Gm³ , with the contributions of 43.8% rice, 40.0% wheat, and 16.2% maize. IWP and IE from the crop consumption perspective in all provinces were different from that observed from production perspective, and the effect of crop supply-demand mismatch on irrigation WUE was comprehensive. Virtual water flow was conducive to water resource conservation and irrigation WUE improvement when judged by IWP. However, the result was just the opposite when IE was used as the evaluation. Improving IWP in the North China Plain and Southeast and optimizing trade structure in Northeast and Southwest contribute to national irrigation water conservation from both of the production and consumption perspectives. The evaluation framework proposed in current paper can inspire the research on agricultural water assessment, management and regulation combining the physical and virtual water. • An assessment framework for irrigation performance coupling physical and virtual water was established. • Irrigation water use efficiency of cereals in China from production and consumption perspective was quantified. • Intra-national virtual crop and water commutation improved irrigation water productivity by 6.8% in China. • Optimizing crop trade structure in Northeast and Southwest contribute to national irrigation water-saving achievement. [ABSTRACT FROM AUTHOR]

Abstract: Wetlands in irrigated agricultural areas have great environmental benefits as agricultural pollution sinks; but agricultural development and water resources redistribution have caused these wetlands to diminish rapidly worldwide. This is the case in the YinNan Irrigation District (YNID) in the upper reaches of the Yellow River in China, where wetlands once flourished as the result of large amount of irrigation diversion and low irrigation efficiency. In this paper, we presented an analytical study on the impact of irrigation water saving practices on wetland distribution in YNID; we also discussed the effect of considering wetland water consumption as beneficial or efficient use on the overall water use efficiency. The study area has a maximal wetland to farmland areal ratio of 10.5% during the irrigation season due to recharges from canal seepage and field percolation; and 45% of the wetland area remains as the permanent pool area during the non-irrigation season. The observed maximum water table rise in the irrigation season is 1.5m. The current irrigation system efficiency in YNID is 0.30, which is a product of the field level efficiency of 0.68 and the conveyance efficiency of 0.44. Our analysis presented in this paper shows that improving the application efficiency to 0.90 at the field level will reduce the maximum water table rise by 0.53m, causing the wetland area to shrink by 17% and the subsequent wetland water consumption to decrease by 11%; further improving conveyance efficiency to 0.60 will reduce the maximum water table rise by 0.95m, causing the wetland area to shrink by 30% and the subsequent wetland water consumption to decrease by 19%. These results indicate that water saving at the conveyance level will have greater impact on wetland water use than that at the field level. If wetland water consumption is considered as efficient use, this fraction of the irrigation water loss becomes efficient use, which will increase the system efficiency proportionally by the percentage of wetland water consumption. The amount of wetlands, and thus additional beneficial wetland water use, is directly dependent on the amount of traditional water losses, such as wetland consumption here. The key question then becomes: where lies the optimum level or the acceptable balance between increasing efficiencies at irrigation scheme level while providing optimal beneficial use for wetlands. [Copyright &y& Elsevier]

• Both the combination and temperature-based ET 0 estimating equations were compared for four main climatic regions across China. • The most accurate method of ET 0 estimating was recommended for each climate region. • The Penman-Monteith Forecast and Temperature Penman-Monteith equations usually provided the most accurate ET 0 estimation. • The Thornthwaite and McCloud would not be recommended for ET 0 estimating in China. Accurate estimation of daily reference evapotranspiration (ET 0) are vital for water resource management and irrigation decision-making. Based on the public weather forecasts, numerous models have been successfully used for daily ET 0 estimating, while too many models available for selection, which causes confusion regarding model selection for specific climate regions. In this paper, the estimating performances of six ET 0 equations using public weather forecast for a lead time of 1–7 days were compared for four main climatic region across China, and then, the most accurate equation was recommended for each climate region. Meanwhile, the applicability of every equation was assessed in relation to four climates, including subtropical monsoon climate (Cwa), temperate continental climate (Dfc), temperate monsoon climate (Dwa) and mountain plateau climate (HG). The Penman-Monteith Forecast (PMF) equation, which consisting of an adaptation of FAO56-PM equation using temperature and weather type forecast as inputs, provided the best ET 0 estimation performance in Cwa and HG climates; and the Temperature Penman-Monteith (PMT) equation using only the temperature data, obtained the most accurate average results for the Dwa and Dfc climates. The best and the second best estimation performance for each climate usually provided by PMF and PMT equations, since they both have the same advantage of following the conceptual approach of the FAO56-PM equation; further the third and the fourth choice would be the Hargreaves-Samani (HS) and the Blaney-Criddle (BC), respectively, while the Thornwaite (TH) and the McCloud (MC) yielded high errors and may not be applicable for ET 0 estimation for most climatic regions. As a whole, the PMF and PMT equations were better than the other equations and thus these two equations were recommended for daily ET 0 estimation for the near-future at all climate regions across China. [ABSTRACT FROM AUTHOR]

Highlights • Distributed modeling of agro-hydrological processes was conducted in MOIS. • Spatial distribution of ET a , crop yield and deep percolation was analyzed. • Irrigation water use efficiency was systematically evaluated in MOIS. • Regional irrigation water budget was obtained and discussed for entire MOIS. • Suitable water-saving amount and improved irrigation strategies were proposed. Abstract Water use conflicts between agriculture and ecosystem have become a more severe and acute problem in the Heihe River basin (HRB). Excessive irrigation water use in the middle oasis of the HRB has caused gradual deterioration of water quality and eco-environment both in middle and lower HRB. The urgent issue is to make a quantitative analysis and an improvement of irrigation water use in middle oasis. In this paper, distributed agro-hydrological modeling was conducted to access the irrigation water use and potential water-saving in the major irrigation system of middle HRB (MOIS), using the GIS-based SWAP-EPIC model. The modeling work was based on the abundant data from field experiments, remote sensing, surveys and statistics, and previous eco-hydrological studies. The reliability of the distributed simulation was evaluated using the remote sensing data of actual evapotranspiration (ET a). Then, spatial distribution of irrigation water depth, ET a , deep percolation and crop yield and the related impact factors were systematically analyzed in MOIS. Results indicated that only 53% of total applied water was efficiently used through ET a , whereas deep percolation loss and canal conveyance loss accounted for 22% and 25% of the total applied water, respectively. The beneficial water use fraction was still low in MOIS, averaging only 0.70 on field scale and 0.52 on district scale. Water-saving analysis predicted that 15% of irrigation amount could be saved efficiently, with especial emphasis on the rational water allocation and distribution. In addition, our results related to agro-hydrological processes could provide very valuable information for improving the existing watershed hydrological modeling in the HRB. [ABSTRACT FROM AUTHOR]

Abstract: Water shortage in China, particularly in the north and northwest of China, is very serious. The region accounts for half of the total area of China, but has less than 20% of total national available water resources. While the water shortage in this region is severe, irrigation water use efficiency is only about 40%, with a typical agricultural water use efficiency of about 0.46kgm−3. Excessive irrigation in Ningxia and Inner Mongolia has had a significant influence on downstream water users along the Yellow River. It is widely believed that an increase in the agricultural water use efficiency is the key to mitigating water shortage and reducing environmental problems. This paper reviews water-saving agricultural systems and approaches to improve agricultural water use efficiency in the arid and semiarid areas of China. The paper will cover biological mechanisms of water-saving agriculture and water-saving irrigation technologies, including low pressure irrigation, furrow irrigation, plastic mulches, drip irrigation under plastic, rainfall harvesting and terracing. In addition, the paper addresses the compensatory effect of limited irrigation and fertilizer supplementation on water use efficiency and highlights the need to breed new varieties for high water use efficiency. Considerable potential for further improvement in agricultural water use efficiency in the region depends on effective conservation of moisture and efficient use of the limited water. [Copyright &y& Elsevier]

Water, energy and food (WEF) are three basic elements that safeguard human life and socioeconomic development. As the demand for water increases in food and energy production, water scarcity is more prominent globally. WEF Nexus plays an important role in evaluating and alleviating the contradiction between food and energy for water. Based on the water footprint of food and energy in China from 1997 to 2016, this paper used the "Structure-Conduct-Performance" analysis paradigm to evaluate the water competition mechanism. The newly constructed competition mechanism model includes type, conduct and performance. The results showed that the blue water footprint of energy increased from 3.25 Gm³ in 1997 to 12.54 Gm³ in 2016. The blue water footprint of food remained above 200 Gm³ for many years, and competition between food and energy production for water was intensifying. The gray water footprint of energy was increasing yearly, and food reached the maximum value of 181.01 Gm³ in 2014. Through model analysis, the South-to-North Water Diversion has not effectively alleviated water scarcity, and a few provinces were still classified in the water pressure-dominated area. The northern channel of West-to-East Power Transmission only transferred electric energy from water pressure-dominated area, causing the unsustainability coefficients of Inner Mongolia and Yunnan to increase from 0.09 and 0.03 in 1997 to 0.23 and 0.05 in 2016. This paper provides effective policy insights for global challenges facing WEF Nexus from the source, process and end of food and energy production. [Display omitted] • The WEF Nexus internal competition mechanism is evaluated by constructing a model. • The model analysed dominant factor, driving mechanism and feedback effect of competition. • The increasing energy water footprint yearly makes water security more prominent. • This study finds that water scarcity has not been effectively alleviated in China. • Many measures provide policy insights into global challenges facing WEF Nexus. [ABSTRACT FROM AUTHOR]

Accounting for over 70% of global water withdrawals, irrigation plays a crucial role in the development of agriculture. Irrigation water requirement ( WIRR ) will be influenced by climate change due to the alteration in soil water balances, evapotranspiration, physiology and phenology under global warming. This is particularly true for rice, a high water-consuming crop. Therefore, exploring the impact of climate change on rice WIRR is of great significance for the sustainable utilization of water resources and food security. This paper aims to investigate spatially and temporally the responses of rice WIRR to climate change in the middle and lower reaches of the Yangtze River (MLRYR), which is one of the most important rice farming districts in China. With the help of the specially developed rice growing period calculation method and water balance model coupled with rice irrigation scheduling, the impacts of climate change on WIRR for early rice, late rice and single cropping rice during the historical (1961–2012) and future (2011–2100) periods were evaluated. Meanwhile, to consider the uncertainty from climate models in future projection, four GCMs under RCP2.6, RCP4.5 and RCP8.5 emission scenarios from the 5th Coupled Model Intercomparison Project (CMIP5) were employed as the input of the water balance model. The results indicate the following: (1) The days of growing period ( DGP ) for all three types of rice display shortened trends in historical and most future periods. However, in the middle region of the MLRYR, the DGP for early rice and late rice would increase by up to10 days in 2080s under RCP8.5 scenario. (2) Over the past 50 years, the WIRR significantly decreased by 1.58 and 2.10 mm yr −1 for late rice and single cropping rice, respectively. While for early rice, the WIRR only slightly decreased by 0.13 mm yr −1 . (3) Projected future WIRR would increase for all three types of rice in the whole region under RCP4.5 and RCP8.5 scenarios (up to 100 mm), but decrease for single cropping and late rice in the southeast region (up to 40 mm). The results can provide beneficial reference and comprehensive information to understand the impact of climate change on the agricultural water balance and improve the regional strategy for water resource utilization and agricultural management in the middle and lower reaches of the Yangtze River. [ABSTRACT FROM AUTHOR]

In semi-arid northwestern China, the groundwater level continues to decline with the development of the irrigated agriculture, resulting in grassland ecosystem degradation. Threshold water tables play an important role in sustaining both grassland ecology and irrigated agriculture. This paper proposes a new method to calculate the threshold water tables based on the quantification of the transport rate of wetting front, by which the optimal layout of well groups in an irrigation district will be discussed; furthermore, this paper will discuss the advantages of using the threshold water tables as the management target to regulate groundwater pumping and ensure an appropriate water table for the ecological system in the irrigation district. The proposed method is applied to an irrigation district in the West Liaohe River Plain, which is a typical area with mixed agricultural and rural lands in northwestern China. The threshold water table in the case study irrigation district is estimated as 10 m; the interference radii of the pumping wells are 340 m, 270 m and 150 m in three different sub-districts, where the well depth is greater than 100 m, 60–80 m and less than 60 m, and the interference radius values are 225–310 m, 165–225 m and 150 m, respectively. • This paper proposes a new method to calculate the threshold water tables. • Optimizing the layout of pumping wells plays a vital role in ensuring threshold water tables. • Based on the food and ecological security, this article gives the reasonable distances for pumping wells. [ABSTRACT FROM AUTHOR]

Efficient reallocation of existing water supply is gaining importance as demand grows and competitions among users intensify. In extremely arid regions, where deficit irrigation needs to be applied, management decisions on agricultural water allocation are often onerous tasks due to the confliction among water users. This paper presents a hydrological modeling approach to assist decision-makers and stakeholders to resolve potential water-sharing conflicts among water users. We combine the land use map with water distribution methods to solve the water allocation problems in a large basin scale. The model is tested and applied in three steps: (i) calibration and validation of water supply and demand along the Tarim River with a combined hydrological and groundwater model, (ii) developing climate change scenarios, (iii) optimizing agricultural water allocation for the entire Tarim River Basin for these scenarios and deriving of conclusions. The comprehensive management of farmland areas and water distribution strategies are investigated in the model scenarios. The results of these assessments provide opportunities for substantial improvement on water allocation and water right. The access of a user to use the water efficiently should be guaranteed, especially in the lower reaches of the river in the arid land. In practice, the hydrological model assists on decision-making for water resource management in a large river basin, and incentive to utilize water use in an efficient manner. [ABSTRACT FROM AUTHOR]

Accurate estimation of reference crop evapotranspiration (ET 0 ) is important due to its crucial role in determining crop water requirement in irrigated agriculture. Though a great number of models have been developed, their rigorous evaluation with measurements is still lacking, leading to confusion and arbitrariness in model selection. In this paper daily estimates of 16 ET 0 models, including five combination-, six radiation and five temperature-based ones, were compared with weighing lysimeter measurements during crop growing season (April through October) in 2012 at a semiarid site in China. Daily ET 0 was measured by two weighing lysimeters (area 1.3 m × 1.3 m, depth 2.3 m) located in a fescue grass ( Festuca arundinacea Schreb) plot (100 m × 100 m) surrounded by a 167 ha crop, winter wheat rotated with summer maize. We found the models were ranked decreasingly as: FAO-ppp-17 Penman > 1963 Penman > FAO-24 Blaney-Criddle (BC) > 1996 Kimberly Penman > FAO-24 radiation > FAO-56 Penman-Monteith (PM) > FAO-24 Penman > Turc > DeBruin-Keijman > Jensen-Haise > Priestley-Taylor > Hargreaves > Makkink > Hamon > Blaney- Criddle > Mcloud on basis of RMSE (root mean square error). Overall, the combination models performed best with RMSE ranging from 0.93 to 1.32 mm d −1 , followed by the radiation models with RMSE from 1.28 to 1.79 mm d −1 , and the temperature models with RMSE from 1.09 to 2.48 mm d −1 . The best combination model (FAO-ppp-17 Penman) was respectively 29% and 17% more accurate than the best radiation (FAO-24 radiation) and temperature (FAO-24 BC) models. Better performance of the combination and radiation models resulted because they explicitly contain the dominant factors influencing ET 0 . All models tended to overestimate under low evaporative demand while underestimating the measured values under high demand, but on average the combination and radiation methods underestimated by 0.46 mm d −1 and 0.60 mm d −1 , respectively, whereas the temperature method overestimated by 0.21 mm d −1 . All combination and radiation models, and the Hargreaves and FAO-24 BC in temperature method showed robust structure. To improve them future efforts should be on local calibration, but for temperature models showing structure failure focus should be on its optimization. The coefficients of commonly used models were calibrated and related to meteorological variables. Particularly, those of the Priestley-Taylor, Makkink, Turc and the Hamon were enhanced, while those of the Hargreaves and BC were decreased. In climate similar to the current site in China we suggest continued use of the older Penman equations for combination method and the FAO-24 radiation or Turc for radiation method. Meanwhile, two questions need to be addressed in future studies: i) adoption of the FAO-56 PM equation as the sole standard for computing ET 0 and the proper value for surface resistance; and ii) the effectiveness of the later modifications to the original wind function in the Penman equation. [ABSTRACT FROM AUTHOR]

Water rights trading is an effective way to promote efficient water allocation. The implementation of agricultural water rights trading can promote water saving, but may reduce the agricultural production scale in irrigation districts. Compensation for crop virtual water export can increase the benefits of agricultural water use, so as to enhance the competitiveness of economic benefit for agricultural production. This paper analyzed the relationship between agricultural water rights trading and virtual water export compensation, then a bi-level programming model was established with multiple objectives. The model was applied in Hetao irrigation district by using enumeration method. The changes of new water use of different users, benefits of irrigation district and water users with different water prices were analyzed and the optimization schemes were selected. Results show that the model through adjusting price variables including both water rights trading price and virtual water compensation price to optimize the allocation of agricultural water quantity saved among different water users, which at the same time makes both the irrigation management administration and water users get more benefit. The optimized scheme can raise the willingness of water saving in irrigation district, and enhance the competitiveness of agricultural water user against non-agricultural water user. This study provides a new method and scientific basis for the water resource management agency in their policy making. [ABSTRACT FROM AUTHOR]

Supplementary irrigation area in north China is an important agricultural production area, but water shortages have limited the agricultural production considerably. Irrigation is required to ensure crop yield during growth seasons with variable rainfall. Most irrigation schedules are based on typical meteorological years. However, it is very difficult to predict the meteorological information of irrigation year in advance, which limits the planning of irrigation schedules. Therefore, taking the central part of Shanxi Province (supplementary irrigation area) as an example, this study focuses on the optimal irrigation decision-making method of supplementary irrigation area. The irrigation schedule of summer maize from 1970 to 2020 was firstly optimized by using DSSAT model and genetic algorithm. On this basis, a decision-making method based on the ratio of cumulative rainfall to cumulative ETc between plantation date to the current date to determine the irrigation time is developed. The results indicated that using P/ETc (the ratio of cumulative rainfall to cumulative crop water requirement) as the criterion leads to superior decision-making. Two supplementary irrigation events can meet the growth demand of summer maize. Irrigation events decisions were made on days 44 and 58 after summer maize sowing, the accuracy of this method for two irrigation events decisions is 82.35 % and 86.27 %, respectively, and the average accuracy of the two irrigation event decisions was 84.31 %. At the same time, a support vector machine algorithm is used to make decisions about irrigation, comparing the decision accuracy with the results of the decision method proposed in this paper. The accuracy of the support vector machine decisions for the first and second irrigation events was 82.35 % and 80.40 %, respectively, and the average accuracy of the two irrigation event decisions was 81.40 %. The decision model was also superior to that involving support vector machine algorithms for the irrigation decision of summer maize can be used for irrigation decision-making in similar supplementary irrigation areas with variable rainfall. • Genetic algorithm and the DSSAT can effectively optimize the irrigation schedule. • Rainfall/ETc can be used as a criterion to determine the irrigation schedule. • The irrigation decision method is more effective than the SVM algorithm. [ABSTRACT FROM AUTHOR]

Evapotranspiration (ET) plays a vital role in surface energy balance and water management. Paddy rice is one of the most water-intensive crops and a staple food worldwide; thus, paddy field ET estimation is an impactful task. In this paper, an improved Surface Energy Balance Algorithm for Land (SEBALR) model is proposed to estimate the paddy field ET and is validated in different climate zones; it considers the advection effect and its applicable condition at the pixel scale and requires no ground-measured data. SEBALR contains two core modules: rice growth period detection and ET retrieval. SEBALR accurately monitored the planting and harvest dates, with an average error of less than 9 days, except for a paddy field located in the US, which had adopted dry seeding. The comparison between the estimation results and eddy covariance data shows that SEBALR can provide a more precise ET estimation than the original Surface Energy Balance Algorithm for Land, yielding a root mean squared error (RMSE) of 1.02 mm·d-1, mean relative error (MRE) of 22.97% and Pearson's correlation (R2) of 0.790. SEBALR successfully monitored paddy field ET from 2001 to 2019 in Nanchang City (NC), China. Yearly ET did not show an apparent change in trend from 2001 to 2019 in NC. SEBALR can be used to monitor the paddy rice growth period and estimate paddy field ET at a regional scale with limited data, providing helpful information for agricultural practices and water management. ● An improved SEBAL was proposed to quantify the ET advection effect of paddy fields. ● SEBALR can provide rice growth period information and more accurate ET. ● SEBALR can be applied on a large scale for its regional applicability and data independence. ● Paddy fields ET and its driving factors were analyzed from 2001 to 2019 in Nanchang, China. ● The structure and uncertainty of SEBALR were evaluated. [ABSTRACT FROM AUTHOR]

Due to the frequent irrigation and excessive fertilization during the rice production in China, diffuse nitrogen (N) and phosphorus (P) pollution from paddy fields has become a serious environment problem and poses great challenges to national water and food security. Considering the regional heterogeneities of climate, cultivation types and cropping systems of rice planting, many water management strategies have been proposed and implemented to control diffuse N and P pollution. However, the water management optimization at different scales (the field scale, the watershed scale and national scale) is lack of comprehensive analyzed. Here, this paper summarized the characteristics of frequent-used water managements and recommended the optimal water managements after identifying the critical risk periods of diffuse N and P runoff losses at the field scale. The effects of water management optimization on diffuse N and P pollution control at the watershed and national scale were also synthetically reviewed. The results indicated that optimized field water management decreased irrigation water use (38.7–40.0%) and reduced diffuse pollution (25.5–38.8%) without significantly compromising rice yield security (−4.20 to 6.5%). The critical risk periods of diffuse pollution were pre-flooding in the Northeast Plain, pre-flooding, regreening stage for transplanting rice (the seeding-three leaf stage for direct seeding rice) and within 2 weeks after topdressing fertilization in the Yangtze River Basin and Southeast Coast in China. The corresponding water managements for these periods has been proposed after considering the climate, precipitation and fertilization characteristics. Ditches and ponds intercepted water and nutrients and mitigated 6.0–39.0% N and P runoff losses in paddy field watersheds. Furthermore, the extensive implementation of paddy water management optimization (paddy fields, ditches and ponds) combined with other advanced agricultural measures, for example, fertilization optimization, would decrease diffuse N and P pollution by 40.7–80.8% at the watershed scale and 44.7–88.1% at the national scale, respectively. This research provided great insights into the specific characteristics of paddy water managements from the fields, watershed and national scale, proposed optimal water management strategies for the realization of sustainable rice production in China, and also summarized the emerging development trends for future research directions. [Display omitted] • Optimal paddy water managements at field, watershed and national scales were analyzed. • Optimal water managements were proposed for critical risk periods at field scale. • Future emerging prospects of paddy water managements from different scales were proposed. [ABSTRACT FROM AUTHOR]

Efficient irrigation scheduling is crucial for both improving crop production and saving irrigation water use in arid/semi-arid agricultural regions threatened by water shortage and soil salinity. However, irrigation scheduling optimization is hindered by the uncertainties of data and optimization model, and adopting the optimal irrigation scheduling is subject to farmers' acceptance. To effectively tackle these challenges, this paper presents a novel human-machine interactive framework for real-time irrigation scheduling (RIS). The developed modeling framework couples a simulation-optimization model, irrigation farmers, and a data assimilation procedure within the human-machine interactive framework for RIS. The proposed approach is capable of: 1) searching optimal irrigation scheduling through the simulation-optimization model; 2) making actual irrigation decisions based on farmers' experiences, knowledge, behaviors, or optimal solutions; and 3) updating soil water content based on the model simulations and real-time observations at each time period. The RIS is applied to a real-world case in a typical arid agricultural region of China. Based on the comparisons with historical irrigation records and a tradition simulation-optimization model, the proposed RIS can not only achieve higher economic benefit with less irrigation water allocation quotas, but also improve irrigation efficiency. This study contributes to the methodology by integrating computer model, real-time observations and farmers' experiences to optimization modeling framework for supporting sustainable irrigation water management. • A human-machine interactive method is proposed for real-time irrigation scheduling. • Computer model, observation, and farmers' justification are integrated via data assimilation. • The proposed method results in higher profit with less water application than either a conventional optimization model or the history records. [ABSTRACT FROM AUTHOR]

• We examine whether water rights trading can encourage agricultural water conservation. • Water rights trading has a moderation effect on agricultural water conservation via technology improvement. • The moderation effect is driven by two forces: the "revenue-driven" effect and the "industrial water pressure-driven" effect. • There exists bottleneck on the moderated technology improvement due to the reduced water rights supply capacity. Although agricultural irrigation technology in China has been steadily improved for decades, the realized water conservation in the agricultural sector is not as good as expected. This paper examines whether water rights trading can encourage agricultural water conservation through technology improvement. Our fixed effects model specification confirms that water rights trading has a moderation effect on agricultural water conservation via technology improvement. We further identify that the moderation effect is driven by two forces which we label as the "revenue-driven" effect and "industrial water pressure-driven" effect. In general, the revenue effect drives farmers to improve the technology. However, the pressure from industrial water demand has more pronounced effects than the revenue-driven channel. Under the dual pressure of high industrial water consumption and low water endowment, farmers tend actively promote irrigation technology and reduce agricultural water use even if there is no revenue-driven effects. In addition, this paper reveals the existence of bottleneck on the moderated technology improvement, due to the reduced capacity on water rights supply in the agricultural sector. [ABSTRACT FROM AUTHOR]

Does the implementation of agricultural water conservation policy necessarily bring about a reduction in agricultural water extraction? Taking China's National Agricultural Water Conservation Outline proposed in 2012 as an example, this paper uses the data of 31 provinces from 2000 to 2019, and employs an empirical strategy of Difference-in-Differences (DID) to estimate the impact of the agricultural water conservation policy on agricultural water extraction. The results show that the agricultural water conservation policy does not achieve the decline of agricultural water extraction, but increases agricultural water extraction. When addressing contemporaneous water-related policies or estimating in subsample, these results are robust. The possible reason for this phenomenon is that the agricultural water conservation policy promotes agricultural production, especially by increasing the sown area and irrigated area, and the expansion of irrigated area is the main reason for the increase in agricultural water extraction. Moreover, land potentiality for crop production may affect the water-saving effect of the agricultural water conservation policy, in which provinces with higher land potentiality will have less increase in agricultural water extraction caused by the agricultural water conservation policy. Therefore, with the empirical evidence from China, agricultural water conservation policy may not necessarily reduce agricultural water extraction, and this phenomenon is always regarded as rebound effects. In order to avoid the adverse impacts of the rebound effect, agricultural water-saving technologies can be strengthened in areas with high land potentiality for agricultural production, and market-oriented policies, such as water rights reform, can be employed to avoid excessive use of water resources in areas with severe over-extraction. • Water-saving effect of agricultural water conservation policy is estimated. • Agricultural water conservation policy increases water extraction. • Possible reason for increase in agricultural water extraction is clarified. • Increase in agricultural water extraction is interpreted as rebound effects. [ABSTRACT FROM AUTHOR]

Numerous aquatic problems have been produced by the extensive urbanization especially in last decades in eastern China. This paper presents an evaluation of water level alteration induced by urbanization in the Lower Qinhuai river basin, Yangtz River delta in the last half century. Analyses were conducted using Range of Variability Approach, based on the indicator system of hydrologic alteration including 31 water level related parameters. By contrasting the overall alteration range and that of each parameter in 1960–1979 (pre-impact period) and 1980–2008 (post-impact period) the hydrological impact of urbanization was revealed. The results indicate that, 1 the urbanization in 1980s-2010s lead to an expansion of impervious area by 8 times and a sever simplification of river network structure; 2 the average monthly water level increased considerably from the pre-impact to post-impact period due to the urbanization; 3 the low water level is more sensitive to the interference of urbanization, both the magnitude of water level in dry season and minimum low water pulse increased distinctly; 4the Lower Qinhuai river basin was changed with moderate intensity by the urbanization process, with and overall change degree of 42.5%. In conclusion, water level is a remarkable indicator of the river regime response to urbanization in plain river network area. The results of the study would provide support in water resources management in urban development, opening new perspective of the hydrological process evaluation in high urbanized plain catchment. [ABSTRACT FROM AUTHOR]

Due to the national nutrition crisis and the adjustment of planting structure, millet has once again become a widely planted cash crop in Northern China. However, as the climate warms in recent years, drought has occurred frequently and repeatedly in Northern China, which has seriously threatened millet production safety in this area. Therefore, it is urgent to clarify the hazard of millet drought disaster and provide reference for the formulation of millet disaster prevention and reduction measures. In this paper, combined with the water demand of millet in each growth period, Standardized Precipitation Requirement Index (SPRI) was selected to identify and quantify the drought disaster of millet. Considering the impact of different degrees of drought in different growth periods, a hazard assessment model is constructed to evaluate the hazard of millet drought disaster in Northern China under the background of climate change. The results show that: (1) SPRI can well characterize the drought of millet in Northern China. (2) In the context of climate change, millet drought in Northern China shows a trend of increasing intensity and decreasing frequency, and it is possible that millet drought will be even more severe in the future. (3) Combined with the hazard assessment model, millet drought in Northern China will still be dominated by middle hazard in the future, but the areas with high hazard will gradually increase, mainly distributed in northeast China, central and western Inner Mongolia and northern Gansu. The research results can be of great practical significance for the adjustment of agricultural production structure in the future, especially for the sustainable development of agriculture and the formulation of measures to prevent and resist agricultural disasters. [Display omitted] • We apply SPRI to identify millet drought by considering actual water demand. • Future changes of millet drought evaluated by CMIP6-GCM models. • Hazard assessment model was presented combined with disaster loss coefficient. • The areas with high hazard of millet drought will gradually increase in future. [ABSTRACT FROM AUTHOR]

Desertification and salinization are both threats to the ecosystem services in inland river oases of arid regions. Previous studies focus on either desertification or salinization, and there is a lack of joint studies on the two issues. The essential cause of desertification in a transition zone is usually concentrated irrigation water use, which leads to shrink of the subsurface flow field of groundwater, decline of the groundwater level, and loss of groundwater supply to the vegetation. The salinization problem in an oasis area is mainly caused by the local excess groundwater in the oasis, referring to secondary salinization, which leads to salt migration with the groundwater level rise to form salt crystallization at the land surface. Thus, the processes of desertification and secondary salinization are connected, and the solutions to the two problems can be complementary, i.e., by transporting the excess groundwater in the local secondary salinization area to the transition zone area where water is scarce. This paper, taking Luocheng Irrigation District in the Heihe River Basin of northwestern China as an example, estimates 1.76–4.70 million m3 of excess groundwater that can be extracted in the salinized area. Using this amount of water through engineering regulation, it is estimated that the transition zone nearby the irrigation district, which is under desertification threat, can be restored with an area of 23–212 km2. An engineering system is designed for coordinated groundwater regulation and the implementation with an experimental farm in the irrigation district is demonstrated. • Providing a new method to mitigate salinization and desertification in arid areas through groundwater regulation. • Estimating the amount of drainage from salinized oasis area in an irrigation district and the transition zone area to be recovered from desert. • Designing an engineering system for coordinated groundwater regulation. [ABSTRACT FROM AUTHOR]

Water resources are distributed in the form of virtual water through international trade, which influences the water supply and consumption of each country. Therefore, it is of significance to study the driving factors of grain virtual water trade to alleviate water stress and guarantee food security. In this paper, the virtual water volume of grain crops traded between China and countries along the Belt and Road (B&R) from 2000 to 2019 was calculated, and a gravity model using panel data was applied to explore the effect of natural and socioeconomic factors on virtual water trade. The virtual water export from B&R countries to China obviously increased in the twenty years and the contributions of various crops to virtual water were more balanced. The regression results indicate that GDP and exchange rate were positively correlated with virtual water inflow, while per capital water resources, arable land, geographic distance, and population were negative factors that hindered virtual water import. The most powerful driving force for grain virtual water trade is water endowment. GDP is an important driver on importing virtual water for countries without water shortage, and a large number of local water resources will not obviously inhibit the driving force of economic strength. By comparing the contribution of factors to virtual water in the past ten years, it can be found that the contribution rate of distance decreased due to the development of transportation industry which reduced the transportation cost of exporting products. The contribution rate of GDP and exchange rate increased, because economic globalization has promoted the effect of economic factors on grain trade. Therefore, the trade structure of agricultural products should be modified based on the characteristics of virtual water flow. For countries without high economic level but water shortage, export crops with high water consumption be reasonably controlled. [Display omitted] • A gravity model was applied to explore the effect of natural and socioeconomic factors on virtual water trade. • The most powerful driving force is water endowment, which were negative factor that hindered virtual water inflow. • Economic strength is an important driver on importing virtual water for countries without water shortage. • The contribution rate of distance decreased due to the development of transportation industry and economic globalization. [ABSTRACT FROM AUTHOR]

Determining the irrigation demands of rice in a humid region is essential for water conservation through improving rainfall utilization in southern China. In this paper, six representative rice areas in southern China were selected, and the daily reference evapotranspiration (ETo) of the representative stations during 1953–2017 was calculated using the Penman-Monteith method. The daily crop evapotranspiration (ETc) was computed using the single crop coefficient method, and the irrigation scheduling under flood irrigation (FI) was obtained by establishing a field water balance model. The characteristics and trends of the irrigation demand of early, middle and late rice, as well as the irrigation changes under a "double-to-single" cropping pattern, were also analyzed with advanced statistical tests. The results indicated that most of the abundant rainfall was concentrated in the growth period of early rice in southern China. Early rice required less water (135.0 mm) and even no irrigation in some wet years, while middle and late rice required more irrigation water (288.1 mm and 265.2 mm, respectively). The key reasons for the differences in irrigation demand among the three rice types are the amount and distribution characteristics of rainfall during the rice growth period. In addition, the irrigation demands of rice showed a downward trend as a response to a decrease in ETc and the increase in rainfall in the past 60 years, where rainfall was the dominant factor. With this increasing trend of rainfall and its better and efficient utilization in the future, rice irrigation demands may be further reduced or completely stopped. Under the "double-to-single" cropping pattern, irrigation demand decreased by 16% on average, and the irrigation frequency, as well as the drainage volume burden, were simultaneously reduced. • Crop water requirement characteristics of different rice types were analyzed. • Irrigation demands under two rice cropping patterns were compared. • Matching of rainfall and crop water requirement deceases irrigation demands. • Better understanding of the rainfall variability is helpful for saving irrigation water. [ABSTRACT FROM AUTHOR]

Abstract: The paper analyzes village-level irrigation management in water scarce northern China in which farmers’ livelihood is highly dependent on the appropriation of water due to limited livelihood alternatives and demographic structure with the elderly as the majority. Most scholarly works have focus on the organizational dimension of irrigation systems in China, while empirical researches relating to irrigation management so far have not paid enough attention to its institutional arrangements. We examine two cases studies – one with both surface and groundwater irrigation, and the other only with groundwater irrigation – to explore how sets of rules, physical attributes of irrigation systems, and social characteristics of communities jointly shape village-level irrigation management. Institutions of Sustainability framework is employed to facilitate the institutional analysis, through which we further discuss the emergency of self-organizing behaviors and origination of specific irrigation forms. We draw the conclusion that the organization of irrigation should fit not only the physical environment but also the institutional context and there is no one-for-all solution for governing irrigation in the field. In addition, we highlight the importance of the participation of locals in irrigation management as the research indicates the capability of locals to organize them for better use of natural resources on which their livelihoods are highly dependent. Finally, we suggest that irrigation management could be improved in future by introducing water users associations into surface irrigation management and devolving this management directly to water users along with participatory land planning. [Copyright &y& Elsevier]

Abstract: The Geographic Information System (GIS) has been extensively integrated into hydrology and non-point source (H/NPS) pollution modeling. However, few studies have been carried out on the effect of GIS inputs on NPS modeling and the prediction uncertainty related to the combination of different GIS inputs. In this paper, the effect of GIS data on H/NPS simulation was investigated by re-sampling the initial GIS data into new grid sizes and grouping the available GIS maps in all possible ways. The effect of GIS inputs was then quantified by the Soil and Water Assessment Tool (SWAT) in the Daning watershed, China. Based on the results, the GIS inputs had a limited impact on runoff and nitrogen (N) predictions, while sediment and phosphorus (P) simulations were sensitively biased by GIS data. This study further demonstrated that a level (threshold) of GIS resolution existed, within which more precise data would not be of benefit to SWAT prediction. To reduce prediction uncertainty, the digital elevation model (DEM) should be tackled to determine at which resolution the model would perform optimally. [Copyright &y& Elsevier]

Abstract: Conservation of soil water and restoration of vegetation have long been major subjects of concern on the northern Loess Plateau. Revegetation with species such as Korshinsk peashrub (KOP) and purple alfalfa (ALF), as well as with natural revegetation of fallow areas (NAF) have been used extensively. This paper examines the temporal stability of soil water storage (SWS) under these different revegetation types, including under millet (MIL) crops for comparison, grown in adjacent plots on a hillslope intending to provide information relevant to the strategic guidance of revegetation and soil water management practices. SWS was measured at 10-cm intervals in the soil profile to a depth of one meter using a neutron probe on 11 occasions between 2010 and 2011. The results indicated that: (1) time-averaged SWS relative to MIL decreased in the order of KOP (49.4mm), ALF (32.4mm) and NAF (14.9mm) implying that shortages of soil water were induced largely by revegetation and were affected by the plant species. (2) Frequency distributions showed that points with probabilities of 0.5 were not stable between extreme soil water conditions; however, this result might be mitigated or avoided by increasing the sampling density and/or conducting measurement over a longer period. (3) Based on relative difference analysis, the most stable data points underestimated the mean SWS of the plots but were still valuable for precisely estimating the mean SWS of the experimental plot; in addition, among methods for estimating the plot average using representative points, directly using the value of relative difference or their standard deviation, or an index of temporal stability or the mean absolute bias error, no one method consistently performed better than another. (4) ALF presented the most temporally stable patterns among all types of revegetation tested, and vegetation cover and aboveground biomass were the main factors affecting SWS temporal stability. (5) Temporally stable points were located at the mid-slope of the plots. In conclusion, when temporal stability theory was applied to sloping lands mid-slope sampling is likely to give the best results but vegetation characteristics, and in particular vegetation cover should be highlighted. [Copyright &y& Elsevier]

Abstract: Agricultural water productivity (WP) has been recognized as an important indicator of agricultural water management. This study assesses the WP for irrigated (WPI) and rainfed (WPR) crops in the Yellow River Basin (YRB) in China. WPI and WPR are calculated for major crops (corn, wheat, rice, and soybean) using experimental, statistical and empirically estimated data. The spatial variability of WPI and WRR is analyzed with regard to water and energy factors. Results show that although irrigated corn and soybean yields are significantly higher than rainfed yields in different regions of the YRB, WPI is slightly lower than WPR for these two crops. This can be explained by the seasonal coincidence of precipitation and solar energy patterns in the YRB. However, as expected, irrigation stabilizes crop production per unit of water consumption over space. WPI and WPR vary spatially from upstream to downstream in the YRB as a result of varying climate and water supply conditions. The water factor has stronger effects on both crop yield and WP than the energy factor in the upper and middle basin, whereas energy matters more in the lower basin. Moreover, WP in terms of crop yield is compared to that in terms of agricultural GDP and the results are not consistent. This paper contributes to the WP studies by a basin context, a comparison between WPI and WPR, a comparison of WP in terms of crop yield and economic value, and insights on the water and energy factors on WP. Moreover, policy implications based on the WP analysis are provided. [Copyright &y& Elsevier]

Abstract: The Xitiaoxi catchment is one of the most important catchments in the Taihu Basin in southeastern China. It contributes a significant amount of surface runoff and nutrient to Taihu Lake. Understanding the nutrient cycling and identification of critical non-point source pollution in this catchment are therefore of primary importance. In this paper, the Xinanjiang-Nitrogen (XAJ-N) model, a conceptual model of nutrient mobilization and transport is developed by integration of the Xinanjiang rainfall–runoff model, the Integrated Nitrogen CAtchment (INCA) model and the Modified Universal Soil Loss Equation (MUSLE). It is implemented with the environmental modelling language PCRaster and estimates the water fluxes and nutrient loadings on a cell-by-cell basis in daily time steps. The model includes the nitrogen cycling processes of mineralization, leaching, fixation, volatilization, nitrification, denitrification and plant uptake. Nitrogen is assumed to be mobilized by surface runoff and groundwater. The model performance was verified by comparing simulated and measured daily discharge and nutrient loadings. The results showed a fairly good relationship between predicted and observed values. Due to the scarce observed data, the simulation results were also validated using an internal mass balance method and values from the literature. It showed that the modelling approach can be used as a tool to estimate the export of nutrient with a daily resolution at a catchment scale. [ABSTRACT FROM AUTHOR]

Abstract: The North China Plain (NCP) is one of the main productive regions for winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.) in China. However, water-saving irrigation technologies (WSITs), such as sprinkler irrigation technology and improved surface irrigation technology, and water management practices, such as irrigation scheduling have been adopted to improve field-level water use efficiency especially in winter wheat growing season, due to the water scarcity and continuous increase of water in industry and domestic life in the NCP. As one of the WSITs, sprinkler irrigation has been increasingly used in the NCP during the past 20 years. In this paper, a three-year field experiment was conducted to investigate the responses of volumetric soil water content (SWC), winter wheat yield, evapotranspiration (ET), water use efficiency (WUE) and irrigation water use efficiency (IWUE) to sprinkler irrigation regimes based on the evaporation from an uncovered, 20-cm diameter pan located 0–5cm above the crop canopy in order to develop an appropriate sprinkler irrigation scheduling for winter wheat in the NCP. Results indicated that the temporal variations in SWC for irrigation treatments in the 0–60-cm soil layer were considerably larger than what occurred at deeper depths, whereas temporal variations in SWC for non-irrigation treatments were large throughout the 0–120-cm soil layer. Crop leaf area index, dry biomass, 1000-grains weight and yield were negatively affected by water stress for those treatments with irrigation depth less than 0.50E, where E is the net evaporation (which includes rainfall) from the 20-cm diameter pan. While irrigation with a depth over 1.0E also had negative effect on 1000-grains weight and yield. The seasonal ET of winter wheat was in a range of 206–499mm during the three years experiments. Relatively high yield, WUE and IWUE were found for the irrigation depth of 0.63E. Therefore, for winter wheat in the NCP the recommended amount of irrigation to apply for each event is the total 0.63E that occurred after the previous irrigation provided total E is in a range of 30–40mm. [Copyright &y& Elsevier]

Abstract: Remote sensing can provide base information for documenting salinity change and for predicting its future evolution trend. The spatial and temporal distributions of soil salinization of Jiefangzha Irrigation Sub-district, the western part of Hetao Irrigation District of Inner Mongolia in northern China, were determined through analysis of satellite-based remote sensing images. Three Landsat TM/ETM+ satellite images taken during 14 years (1991∼2005) coupled with field observations were chosen as the basic data sources. Supervised classification and visual interpretation were used to analyze salinity classification and statistical method was applied to analyze the relationship between salinity and groundwater depth. From 1991 to 2005 the area of heavy saline land decreased from 191 to 136km2, or 3.9km2 per year; the moderate saline land decreased from 318 to 284km2, or 2.5km2 per year; the slight saline land decreased from 510 to 394km2, or 8.2km2 per year. Therefore, soil salinization in Jiefangzha Irrigation Sub-district is decreasing in general. The electrical conductivity (EC) values measured from field have the following relationship with the reflectance composition obtained from LANDSAT Enhanced Thematic Mapper Plus (ETM+) data: EC=5.653(band5−band7)/(band5+band7)+0.246. In addition, an r 2 value between EC values and groundwater depth is 0.72, which indicates groundwater depth is the major factor for the regional soil salinity control. The paper can serve as a theoretical reference for optimal allocation of irrigation water resource and salinization control in Hetao Irrigation District. [ABSTRACT FROM AUTHOR]

Abstract: In the Lower Yellow River Delta, soil salinity is a problem due to the presence of a shallow, saline water table and marine sediments. Spatial information on soil salinity at the field level is increasingly needed, particularly for better soil management and crop allocation in this area. In this paper, a mobile electromagnetic induction (EMI) system including EM38 and EM31 is employed to perform field electromagnetic (EM) survey, and fast determination and quantitative evaluation of the spatial pattern of soil salinity is discussed using the field EM survey data. Optimal operation modes of EM38 and EM31 are determined to establish multiple linear regression models for estimating salinity from apparent soil electrical conductivity (ECa). Spatial trend and semivariogram are illustrated and spatial distribution of field salinity status is further visualized and quantitatified. The results suggest that ECa (EM38 and EM31) data is highly correlated with salinity, and that the interpretation precision of soil salinity at various layers can be improved using EM38h and EM31h (where h represents the horizontal mode of EM measurement). Both EM38h and EM31h exhibit significant geographic trend. Nested spherical models fit the semivariance of EM38h and EM31h better than single spherical models. Spatial autocorrelation of EM31h is stronger than that of EM38h, and short-range variation is the chief constitute of spatial heterogeneity for both EM38h and EM31h. Quantitative classification shows that soil salinity exhibits the trend of accumulation in the root zone. In 0–1.0m solum, heavy salinized and saline soils are the predominant soil types, accounting for 54% and 41% of total survey area, respectively. The area of light and moderate salinized soils is comparatively small, which accounts for only 0.4% and 4.6%, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Crop reference evapotranspiration (ET 0) is often used to determine crop water requirement. ET 0 maps are useful for regional agricultural and water resources management, and also play an important role in the distributed hydrological modeling. For generating spatial ET 0 surfaces, ‘Interpolate-then-calculate (IC)’ approach is powerful in principle and is recommended especially for sparse weather station networks. The partial thin-plate smoothing spline incorporated in ANUSPLIN for interpolating climatic variables has been accepted widely across the world. In this paper, the climatology monthly ET 0 data of Shiyang river basin, one of the three inner basins in northwest China, are developed by spatially modeling the input climatic parameters with ANUSPLIN, and from the interpolated climate and ET 0 datasets, sensitivity coefficients of ET 0 to the climatic variables of selected months are also spatially distributed. In the cool months (January, February, November and December), the spatial variability of ET 0 is small and the value is rather low, whereas the warm season (May, June, July and August) is characterized by high values of ET 0 and large spatial variations in the river basin. Vapor pressure deficit is the most sensitive variable during the cool months and in the mountainous area with lower temperature; mean air temperature is the least sensitive one during the year and a little variation is observed at the basin scale. In summer, available energy primarily forces ET 0 as expected, and in winter, wind speed plays an important role and affects ET 0 greater at the northern plain region where deserts are dominated by dunes and low shrubs. We conclude that for regions with isolated climate stations, ‘IC’ procedure by including topographic and geographic factors can effectively model spatially distributed ET 0. [Copyright &y& Elsevier]

Abstract: Although the ways in which farmers access irrigation services in areas that rely on groundwater have changed over the past decade, little empirical work has measured the impact of these changes. This is surprising given the potential effects—both positive and negative. In this paper we explore the impacts of the emergence of the markets for irrigation services from groundwater on agricultural production – including crop water use and crop yields – and farmer income in northern China. From a survey of 35 randomly sampled villages and 338 households in two provinces (Hebei and Henan Provinces) in 2001 and 2004, we show that when farmers access water from markets for irrigation services, they significantly reduce water use, compared with farmers who have their own tubewells. However, there is no significant difference between the volume of water used by farmers who access irrigation services provided by the village, and the volume used by farmers who access water from markets for irrigation services. Importantly, although water use decreases, we find little effect on either agricultural productivity (yields) or income. [Copyright &y& Elsevier]

Abstract: Serious water deficits and deteriorating environmental quality are threatening agricultural sustainability in the North China Plain (NCP). This paper addresses spatial and temporal availability of water resources in the NCP, identifies the effects of soil management, irrigation timing and amounts, and crop genetic improvement on water use efficiency (WUE), and then discusses knowledge gaps and research priorities to further improve WUE. Enhanced irrigation and soil nutrient (mainly nitrogen) management are the focal issues in the NCP for enhancing WUE, which are shown to increase WUE by 10–25% in a wheat–maize double cropping system. Crop breeding has also contributed to increased of WUE and is expected to play an important role in the future as genetic and environmental interactions are understood better. Agricultural system models and remote sensing have been used to evaluate and improve current agronomic management practices for increasing WUE at field and regional scales. The low WUE in farmer''s fields compared with well-managed experimental sites indicates that more efforts are needed to transfer water-saving technologies to the farmers. We also identified several knowledge gaps for further increasing WUE in the NCP by: (1) increasing scientific understanding of the effects of agronomic management on WUE across various soil and climate conditions; (2) quantifying the interaction between soil water and nitrogen in water-limited agriculture for improving both water and nitrogen-use efficiency; (3) improving irrigation practices (timing and amounts) based on real-time monitoring of water status in soil-crop systems; and (4) maximizing regional WUE by managing water resources and allocation at regional scales. [Copyright &y& Elsevier]

Abstract: In the North China Plain (NCP), while irrigation using groundwater has maintained a high-level crop productivity of the wheat–maize double cropping systems, it has resulted in rapid depletion of groundwater table. For more efficient and sustainable utilization of the limited water resources, improved understanding of how crop productivity and water balance components respond to climate variations and irrigation is essential. This paper investigates such responses using a modelling approach. The farming systems model APSIM (Agricultural Production Systems Simulator) was first calibrated and validated using 3 years of experimental data. The validated model was then applied to simulate crop yield and field water balance of the wheat–maize rotation in the NCP. Simulated dryland crop yield ranged from 0 to 4.5tha−1 for wheat and 0 to 5.0tha−1 for maize. Increasing irrigation amount led to increased crop yield, but irrigation required to obtain maximum water productivity (WP) was much less than that required to obtain maximum crop yield. To meet crop water demand, a wide range of irrigation water supply would be needed due to the inter-annual climate variations. The range was simulated to be 140–420mm for wheat, and 0–170mm for maize. Such levels of irrigation applications could potentially lead to about 1.5myear−1 decline in groundwater table when other sources of groundwater recharge were not considered. To achieve maximum WP, one, two and three irrigations (i.e., 70, 150 and 200mmseason−1) were recommended for wheat in wet, medium and dry seasons, respectively. For maize, one irrigation and two irrigations (i.e., 60 and 110mmseason−1) were recommended in medium and dry seasons, while no irrigation was needed in wet season. [Copyright &y& Elsevier]

Abstract: The main purpose of this paper was to evaluate whether or not the dual crop coefficient (DCC) method proposed in FAO-56 was suitable for calculating the actual daily evapotranspiration of the main crops (winter wheat and summer maize) in the North China Plain (NCP). The results were evaluated with the data measured by the large-scale weighing lysimeter at the Yucheng Comprehensive Experimental Station (YCES) of the Chinese Academy of Sciences (CAS) from 1998 to 2005 using the Nash-Sutcliffe efficiency (NSE), the root mean square error (RMSE) and the root mean square error to observations’ standard deviation ratio (RSR). The evaluation results showed that the DCC method performed effective in simulating the quantity of seasonal evapotranspiration for winter wheat but was inaccurate in calculating the peak values. The RMSE value of the winter wheat during the total growing season was less than 0.9mm/d, the NSE and RSR values during the total growing stage were “Very Good”, but the results for summer maize were “Unsatisfactory”. The recommended basal crop coefficient values K cbtab during the initial, mid-season and end stages for winter wheat and summer maize were modified and the variation scope of basal crop coefficient K cb was analyzed. The K c (compositive crop coefficient, K c = ET c /ET 0, ET c here is the observed values by lysimeter, ET 0 is the reference evapotranspiration) values were estimated using observed weighing lysimeter data during the corresponding stages for winter wheat and summer maize were 0.80, 1.15, 1.25, 0.95; 0.90, 0.95, 1.25, 1.00, respectively. These can be a reference for irrigation planning. [Copyright &y& Elsevier]

Abstract: Flooding regimes in arid and semi-arid regions are heavily influenced by climate change and water shortage, water regulations, and increased water demands. Wetlands managed as part of regulated water systems in agricultural landscapes often require external water supplies to sustain or support desired properties or services. Therefore, water resource managers must weigh water requirements necessary to support wetland functions alongside other water demands. This paper presents a simple method of using a modified climate diagram to display net water requirements for a managed wetland in Xi’an, China. The net water requirements were estimated using the DRAINMOD simulation model by assuming that evaporation is the only path for water loss. For this case study, the ratio of water supply to air temperature was adjusted to 1:1. Three water supply estimates were generated to support a desired water table depth of 30cm for 5%, 12.5%, and 25% of the growing season in Xi’an. When water supply reaches or exceeds a curve, it creates a wetter condition than that represented by the curve. The results also indicate that timing of recharge is very important in preserving wetland hydrology in dry regions. This modified climate diagram prompts an intuitive understanding of the relationship between recharge and consequent wetness of a wetland. It may be used as a standard tool for determining adequate water demand in arid regional water resources management that considers wetland protection or restoration. [Copyright &y& Elsevier]

Abstract: Accurate estimation of the reference crop evapotranspiration (ET 0) is investigated due to its critical role in affecting calculation of crop water use and efficiency in agricultural ecosystems. The main emphasis in this paper is to clarify the possible uncertainty in the estimation of ET 0 associated with using un-calibrated Ångström–Prescott (A–P) coefficients. We first calibrated the coefficients using long-term data records from 34 sites in the Yellow River basin in China, and then applied these coefficients to estimate short wave irradiance (R s ) and ET 0 at 16 sites to evaluate the difference in ET 0 between the FAO recommended and the locally calibrated. We found that the direct use of the FAO recommended coefficients significantly affected the estimation of ET 0 at most sites, which differed from −3% to 15% at daily scale and from −4% to 16% at monthly scale from the locally calibrated ones. These differences are comparable with or larger than those caused by some alternatives of the FAO recommended algorithms for net irradiance or vapor pressure, which further highlights the importance of using the locally calibrated coefficients. The degree of difference in ET 0 showed a significant threshold relation with altitude and longitude in such a way that relatively small impact lies around 2233m and 98°E, and away from these, the effect begins to increase. Given the large overestimation in water use as a consequence of the significant overestimation in ET 0 associated with the direct use of the FAO coefficients, especially in those high yield production areas with altitude <1200m, we developed several relationships between the A–P coefficient a, b, (a + b) and other easily obtainable factors (altitude, longitude and air temperature). A three-step procedure was recommended in applying these relations, which was (1) determine if calibration is needed or not for a given location; (2) estimate one of the A–P coefficients, either a or b if calibration is needed; (3) estimate the remaining coefficient using relations of (a + b) due to its higher coefficient of determination. In summary, we have revealed the errors and areas that are most affected when using the un-calibrated coefficients, and discussed the consequence of such error on agricultural production, and proposed practical solutions to avoid large errors. These results are intended to make the research community aware of such errors so that more appropriate choice of these coefficients is made. We hope that similar assessment will be done in other climates, contributing to managing water resources efficiently in water basins. [Copyright &y& Elsevier]

Abstract: Crop evapotranspiration (ET) is an important component of simulation models with many practical applications related to the efficient management of crop water supply. The algorithms used by models to calculate ET are of various complexity and robustness, and often have to be modified for particular environments. We chose three crop models with different ET calculation strategies: CROPWAT with simple data inputs and no calibrations, MODWht for intensive inputs and limited calibrations, and CERES-Wheat with intensive inputs and more calibrations for parameters. The three crop models were used to calculate ET of winter wheat (Triticum aestivum L.) grown at two experimental sites of China and US during multiple growing seasons in which ET was measured using lysimeter or soil water balance techniques. None of the models calculated daily ET well at either Bushland or Zhengzhou as indicated by high mean absolute differences (MAD>1.1mm) and root mean squared errors (RMSE>2.0mm). The three models tended to overestimate daily ET when measured ET was small, and to underestimate daily ET when measured ET was large. The fitted values of daily crop coefficients (K c), calculated from daily ET and reference ET (ETo), were very similar to those of Allen et al. (1998) [Allen, R.G., Pereira, S.L., Raes, D., Smith, M., 1998. Crop evapotranspiration guidelines for computing crop water requirements. Irrigation and drainage paper 56, Rome] although some K c were overestimated (≥1.0). Leaf area index (LAI) was poorly calculated by MODWht and CERES-Wheat, especially when using the Priestley–Taylor method to estimate potential ET (PET). Poor overall ET calculation of three models was associated with poorly estimated values of PET or ETo, K c and LAI as well as their interactions. Therefore, this suggested that considerable revisions and calibrations of ET algorithms of the three models are needed for the improvement of ET calculation. [Copyright &y& Elsevier]

Abstract: Irrigation and fertilization management practices play important roles in crop production. In this paper, the Root Zone Water Quality Model (RZWQM) was used to evaluate the irrigation and fertilization management practices for a winter wheat–summer corn double cropping system in Beijing, China under the irrigation with treated sewage water (TSW). A carefully designed experiment was carried out at an experimental station in Beijing area from 2001 to 2003 with four irrigation treatments. The hydrologic, nitrogen and crop growth components of RZWQM were calibrated by using the dataset of one treatment. The datasets of other three treatments were used to validate the model performance. Most predicted soil water contents were within ±1 standard deviation (S.D.) of the measured data. The relative errors (RE) of grain yield predictions were within the range of −26.8% to 18.5%, whereas the REs of biomass predictions were between −38% and 14%. The grain nitrogen (N) uptake and biomass N uptake were predicted with the RE values ranging from −13.9% to 14.7%, and from −11.1% to 29.8%, respectively. These results showed that the model was able to simulate the double cropping system variables under different irrigation and fertilization conditions with reasonable accuracy. Application of RZWQM in the growing season of 2001–2002 indicated that the best irrigation management practice was no irrigation for summer corn, three 83mm irrigations each for pre-sowing, jointing and heading stages of winter wheat, respectively. And the best nitrogen application management practice was 120kgNha−1 for summer corn and 110kgNha−1 for winter wheat, respectively, under the irrigation with TSW. We also obtained the alternative irrigation management practices for the hydrologic years of 75%, 50% and 25%, respectively, in Beijing area under the conditions of irrigation with TSW and the optimal nitrogen application. [Copyright &y& Elsevier]

Abstract: The Zhanghe Irrigation System (ZIS), in Central China, has drawn attention internationally because it managed to sustain its rice production in the face of a dramatic reallocation of water to cities, industries and hydropower uses. Ponds, the small reservoirs ubiquitous in the area, are hypothesized to have been instrumental in this. Ponds are recharged by a combination of return flows from irrigation and runoff from catchment areas within the irrigated perimeter. They provide a flexible, local source of irrigation water to farmers. This paper assesses the storage capacity and some key hydrological properties of ponds in a major canal command within ZIS. Using remote sensing data (Landsat and IKONOS) and an area–volume relationship based on a field survey, we obtained an overall pond storage capacity of 96mm (per unit irrigated area). A comparative analysis between 1978 and 2001 reveals that part of this capacity results from a very significant development of ponds (particularly in the smaller range of sizes) in the time interval, probably as a response to rapidly declining canal supplies. We developed a high-resolution digital elevation model from 1:10,000 topographic maps to support a GIS-based hydrological analysis. Pond catchments were delineated and found to extensively overlap, forming hydrological cascades of up to 15 units. In a 76-km2 area within the irrigation system, we found an average of close to five ‘connected’ ponds downstream of each irrigated pixel. This high level of connectivity provides opportunities for multiple reuses of water as it flows along toposequences. A fundamental implication is that field ‘losses’ such as seepage and percolation do not necessarily represent losses at a larger scale. Such scale effects need to be adequately taken into account to avoid making wrong assumptions about water-saving interventions in irrigation. [Copyright &y& Elsevier]

Abstract: Using a binary logistic regression model, this paper evaluates the determinants of farmers’ decisions to adopt rainwater harvesting and supplementary irrigation technology (RHSIT) and its elasticity of adoption in the rain-fed farming systems, based on a survey of 218 farmers in the semiarid areas of Loess Plateau in 2005. The results indicate that 12 variables are significant in explaining farmers’ adoption decisions. Farmers’ educational background, active labor force size, contact with extension, participation in the Grain-for-Green project, and positive attitudes towards RHSIT are some of the variables that have significantly positive effects on adoption of RHSIT, while farmer''s age and distance from water storage tanks to farmers’ dwellings have significantly negative correlation with adoption. The probability of adoption also increases with increased targeting of institutional variables: credit obtained, assistance obtained, and technical training received. Farmers in villages that have more erosion problems are more likely to adopt RHSIT. Besides, the model indicates that a 1 unit increase in the diversity of irrigated crops grown by a household, especially high-value crops, results in a 6.98 times increase in the probability of RHSIT adoption. Variables such as family size, off-farm activity, level of family income, risk preference, and land tenure do not significantly influence adoption. This information will help prioritize the factors that affect adoption decisions and provide insight on pathways to increase the adoption of RHSIT. [Copyright &y& Elsevier]

Abstract: Tradable water rights systems are becoming an important way to achieve distributive efficiency for water resources. However, it is not easy for countries or regions to establish water markets due to the existence of various barriers. In early 2002, the Ministry of Water Resources (MWR) of China initiated an experimental project—Building Water-saving Society in Zhangye City. This project was the first of its kind in China. The aim of the project was to establish a new water use rights (WUR) system with tradable water quotas and to reallocate water resources reasonably and efficiently through market-based instruments. This paper presents the research done on the system and water markets. It has been found that that the system is hard to implement well and that WUR trading is not popular. The barriers to implementing a WUR system are social and administrative in nature. WUR trading faces management, legal, administrative, and fiscal barriers. We discuss why these barriers exist and we provide policy recommendations to overcome them. [Copyright &y& Elsevier]

Abstract: The YinNan Irrigation District (YNID) is located in the upper reaches of the Yellow River in NingXia, China. Its drainage system was constructed between the 1950s and 1970s to maintain salt and water balances in the district. The system, however, has been reported draining the agricultural lands excessively, resulting in frequent irrigations and large amount of drainage discharge into the Yellow River each year. This paper presents a comprehensive analysis of current drainage practices in the YNID and discusses the feasibility of controlled drainage in order to mitigate the negative impact of agricultural drainage. Based on historical records and available information, drainage discharge has been estimated for different crop fields and ditches. The results show that for the major water use crop, rice, controlled drainage may reduce subsurface discharge through field ditches up to 94%. For wheat and corn, the benefit of controlled drainage is not significant because the major drainage discharge is directly through the main ditch system and the Yellow River channel. The rotational cropping nature and local water management tradition, however, make controlled drainage a very attractive option for water savings and reducing water pollution to the Yellow River. [Copyright &y& Elsevier]