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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]

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]

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]

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: 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 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: 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: 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]

In the agricultural water resources system, the regional yield is hard to be simulated accurately under the impacts of spatial heterogeneities of soil, weather, and crop types. The optimal water allocation schemes may be not in accordance with actual conditions due to neglecting the actual crop growth process. Meanwhile, the uncertainties in the simulation-optimization models are not easy to be addressed. To deal with the above problems, this paper develops a framework of the distributed AquaCrop simulation nonlinear multi-objective dependent-chance programming (distributed AquaCrop NMOFDCP) for irrigation water resources management under uncertainties. This developed model is applied to a case study of irrigation water resources management in the middle reaches of the Heihe River Basin in China. The 134 homogeneous decision-making units (DMUs) are divided to depict the spatial heterogeneities of the study area, and 472 decision variables (irrigation amount) for 134 DMUs are optimized. Moreover, the model deals with uncertainties expressed as fuzzy goals and tradeoffs relationships between objectives of the yield and water productivity, and measures the satisfactory degrees between objectives and their fuzzy goals. Two groups of Pareto solutions corresponding to the maximum satisfactory degree of the yield, and the maximum satisfactory degree of the water productivity are obtained by the parallel genetic algorithm (PGA) method respectively. In addition, water allocation, satisfactory degree of the yield, and satisfactory degree of water productivity are analyzed at the decision-making unit scale, crop scale, and irrigation-district scale separately. Besides the effects of three weather conditions and four soil types on the system's outputs are conducted. The results show that weather conditions and soil types have obvious effects on the system's outputs at three analysis scales, and different water allocation patterns at the growth period affect the yield and water productivity. • A distributed AquaCrop model considering spatial heterogeneities of soil, crop, weather and irrigation is developed. • A nonlinear multiple-objective fuzzy dependent-chance programming is proposed. • A distributed simulation-optimization model is built for irrigation water resources management. • The model is used to a case study of Heihe River Basin, China to verify its application. [ABSTRACT FROM AUTHOR]

Improving water-saving irrigation technology and water use efficiency are often regarded as effective ways to control the amount of agricultural water consumption, but the rebound effect may offset this effort in practice. Based on the sample of 30 provinces in China from 2000 to 2017, this paper applies the meta frontier data envelopment analysis method to measure agricultural water efficiency, and then estimates the rebound rate of agricultural water resource applying difference-generalized method of moments and elasticity analysis formula. Further, the difference-in-difference model is used to test the effectiveness of China's water rights reform on China's agricultural water rebound rate in recent years. The results show that: (1) Within the survey period, the average agricultural water rebound rate of China in short-term and long-term were 0.49 and 0.66 respectively, and the water rebound rate in all provinces were positive, indicating that water rebound effect was widespread in China's agricultural water market; (2) Agricultural water rebound rates were significantly different among regions, which was higher in western region while were comparatively smaller in the eastern and central regions; (3) The water rights pilot project failed to restrain the rebound of agricultural water use, but promoted it, which may be resulted from the market frictions of water trade. According to the results, recommendations are put forward for the governments to reinforce management of water, improve water rights system and reduce trade costs, in order to reduce the friction of agricultural water market and the effective use of water resource. • We used meta frontier DEA to measure agricultural water efficiency. • We estimated agricultural water rebound rates in the short and long run. • The effectiveness of China's water rights reform is tested. [ABSTRACT FROM AUTHOR]

The spatial heterogeneity of yield caused by the interactions between soil types, and crop types, the nonlinear relationship between yield and irrigation, and risks and uncertainties in the process of decision making make water allocation become a challenging task. To address the above problems, this paper proposed a framework that couples the distributed AquaCrop simulation model with a risk-based probabilistic-possibilistic programming with fuzzy random coefficients optimization model. Compared with the conventional optimization models, it can make the optimal water allocation schemes based on the actual crop growth process, at the same time with considerations of multiple uncertainties expressed as fuzzy random variables and stochastic variables, and the water-shortage risk expressed as the water uniform-scarcity index (WUSI). Besides, it can address the relationship between the objective function with fuzzy random coefficient and fuzzy goals set by decision-makers through the permissible levels. Moreover, three risk scenarios with three water availability-violated probabilities, three allowable water-shortage risk levels, and three predefined objective-probability levels of water allocation, yield, and permissible level are examined, and influenced degrees of above risk parameters on system's outputs are explored by the sensitivity analysis method. The developed model is used to a case study of irrigation water resources management in the Yingke district (YID), Heihe River Basin, China. The results show that the optimal water allocation schemes and permissible level have different responses on risk parameters and the developed model can tradeoff the relationships amid water allocation, water-shortage risk, yield, and permissible levels. It can help managers to identify desired decision alternatives in water allocation schemes among different crops in different soil types and different risk levels. • The risk-based probabilistic-possibilistic programming with fuzzy random coefficients is developed. • The agricultural water resources risk management based on the distributed simulation-optimization model is established. • The effects of the single risk parameter on the system's outputs are conducted by the sensitivity analysis method. • The developed model is used to a case study to verify its application. [ABSTRACT FROM AUTHOR]

• Hybrid framework for agricultural water utilization and efficiency evaluation was constructed. • WRU, WRE and WRP are water appropriation amount, effective rate and production ability measurement. • Water use efficiency in China promoted over time while varied among both regions and crops. • Indices in hybrid framework were novelty and unique on scientific nature and spatial performance. Efficient agricultural water use is required for food safety and water alleviation on a global scale. Combining the water footprint and agricultural water use paradigms and enveloping water resource movement and its impact on the environment in the agricultural production process, a hybrid framework for agricultural water utilization and efficiency evaluation was constructed in the current paper. The indicators water resources use (WRU), efficiency (WRE) and productivity (WRP) are used in this framework for the total water exploitation, the effective utilization rate and the production capacity measurement, respectively. An empirical study on the framework was conducted with major cereals (wheat, maize and rice) in 31 provinces, autonomous regions and municipalities (PAMs) of China. The national WRU, WRE and WRP values of integrated cereal were calculated to be 669.0 G m³, 0.633 and 0.679 kg/m³, respectively, from 1996 to 2015. The PAMs with high WRE values were located in southwestern, northeastern and northern China, while the ones with low values were clustered in northwestern and southeastern China. The spatial distribution pattern of WRP is consistent with precipitation. The water use efficiency (WRE and WRP) of the three specific crops in this framework increased over time. The WRE of maize was significantly higher than that of rice and wheat, while the WRP of wheat was the lowest. WRU measures the total water resource appropriation during crop growth in both quantity and quality; WRP was able to show where water use efficiency needs to be improved; and the function of WRE to indicate water saving potential could not be replaced by notable indices, such as irrigation efficiency or generalized efficiency. Therefore, further research is warranted to evaluate agricultural water use efficiency at different scales using this hybrid framework. [ABSTRACT FROM AUTHOR]