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Land use change greatly affects the runoff characteristics of the basin, which in turn affects the distribution of surface water and groundwater in the region. Quantitative analyses of the hydrological response of watershed runoff to land use change are conducive to the formulation of sustainable water resource strategies. In this paper, the impact of land use change on runoff characteristics in the Jing River Basin was evaluated using the SWAT model, the land use pattern of the Jing River Basin in 2040 was predicted using CA-Markov model, and five land use change scenarios were set up in combination with the trend of land use transfer, and the response relationship between land use change and runoff hydrological characteristics in the basin was studied. The results show that the land use changes reduce runoff and change the hydrological cycle process of the basin. The hydrological response of different land use types varies significantly, but only has a less impact on annual runoff. Farmland has a promoting effect on production flow; woodland and grassland are not conducive to the formation of surface runoff and will increase underground runoff and evapotranspiration in the basin. The increase in vegetation coverage after returning farmland to woodlands and grasslands has reduced surface runoff, increased the recharge of groundwater, and played a positive role in ecological restoration in the river basin. The research results are of great significance for understanding the hydrological consequences of land use change and the rational planning of land use patterns in river basins. [ABSTRACT FROM AUTHOR]

The changes of runoff in the middle reaches of the Yellow River basin of China have received considerable attention owing to their sharply decline during recent decades. In this paper, the impacts of rainfall characteristics and land use and cover change on water yields in the Jingle sub-basin of the middle reaches of the Yellow River basin were investigated using a combination of statistical analysis and hydrological simulations. The Levenberg Marquardt and Analysis of Variance methods were used to construct multivariate, nonlinear, model equations between runoff coefficient and rainfall intensity and vegetation coverage. The land use changes from 1971 to 2017 were ascertained using transition matrix analysis. The impact of land use on water yields was estimated using the M-EIES hydrological model. The results show that the runoff during flood season (July to September) decreased significantly after 2000, whereas slightly decreasing trend was detected for precipitation. Furthermore, there were increase in short, intense, rainfall events after 2000 and this rainfall events were more conducive to flood generation. The "Grain for Green" project was carried out in 1999, and the land use in the middle reaches of the Yellow River improved significantly, which make the vegetation coverage (Vc) of the Jingle sub-basin increased by 13%. When Vc approaches 48%, the runoff coefficient decreased to the lowest, and the vegetation conditions have the greatest effect on reducing runoff. Both land use and climate can change the water yield in the basin, but for areas where land use has significantly improved, the impact of land use change on water yield plays a dominant role. The results acquired in this study provide a useful reference for water resources planning and soil and water conservation in the erodible areas of the middle reaches of the Yellow River basin. [ABSTRACT FROM AUTHOR]

Recently, local floods have become severely threatening to urban safety in China. As the capital city, Beijing has experienced serious local floods every year. In this paper spatial characteristics of local floods in the Beijing urban area were studied. Local flood locations changed and appeared as a spatial expansion trend from 1981 to 2011. Since all of the local floods were located in built-up areas, we further studied the relation between local floods and built-up areas using the spatial statistics of Geographic Information Systems. The results show that they had the same directional development trend which indicated local floods would get worse with the expansion of built-up areas. It also found that most local floods were located where there were high densities of drainage pipes, so we could infer that pipe systems should not be the only way to solve local floods due to their failures and negative effects. [ABSTRACT FROM AUTHOR]

To reveal the influence process of land use changes on runoff variation trends, this paper takes the Luojiang River of China as the study area, and the Soil and Water Assessment Tool (SWAT) model was constructed to quantitatively analyze the impact of different land uses on runoff formation in the watershed, and used the Cellular Automata-Markov (CA-Markov) model to predict future land use scenarios and runoff change trends. The results show that: (1) the SWAT model can simulate the runoff in the Luojiang River basin; (2) the runoff in the Luojiang River basin has a decreasing trend in recent 10 years, caused by the decrease of rainfall and runoff due to changes in land use; (3) the forecast shows that the land-use changes in the basin will lead to an increase in runoff coefficient in 2025. The increase of the runoff coefficient will bring some adverse effects, and relevant measures should be taken to increase the water storage capacity of urban areas. This study can help plan future management strategies for the study area land coverage and put forward a preventive plan for the possible adverse situation of runoff variation. [ABSTRACT FROM AUTHOR]

• Parameter uncertainty varies over time scales due to land use change (LUC). • The calibrated daily runoff model is deficient for the extreme flow changes. • Model structure impacts the extreme runoff direction change for moderate LUC. Hydrological modeling has provided key insights into the mechanisms of land-use change impacts on runoff. However, the uncertainty of this impact is poorly understood. This paper examines the uncertainty originated from hydrological models' parameters and structure in simulating hydrological responses to land use change on daily, monthly and annual time scales. Two hydrological models, SWAT and HSPF, were applied to simulate the runoff response in the Xitiaoxi basin of eastern China. The effects of three land use scenarios (in 1985, 2002 and 2014) were analyzed with respect to the expansion of urban areas and reduction of cropland and forests. The changes in streamflow with multi-timescales between two models were compared at the whole basin and the sub-basin scales. The parameter uncertainty was estimated based on a sequential uncertainty analysis method (SUFI-2). The results indicate that the two models (SWAT and HSPF) could reproduce the observed daily and seasonal flows well, but they cannot accurately reconstruct the extreme flows (such as annual 7-day minimum discharge, R_7dMIN). The effect of parameter uncertainty on streamflow varies over time scales. The simulated annual and monthly runoff change values show large discrepancies but with same trends. The simulated changes for annual maximum discharge (R_1dMAX) and R_7dMIN often show different signs. The average width of the predictive interval in the relative change of different flow characteristics exceeded 100% of the average relative changes for both models. HSPF tends to present larger relative changes for the annual and monthly runoffs compared to SWAT. Moreover, the model choice could affect the direction change in R_1dMAX and R_7dMIN. However, when land use change was significant to a certain degree, both models simulated increased R_1dMAX and decreased R_7dMIN, but with different significance levels. The study suggests that the model structure represents an additional uncertainty, which should be accounted for in the land-use change impact assessment. [ABSTRACT FROM AUTHOR]

Abstract: Land use change has significant impacts on hydrologic processes at the watershed level. This paper combines an empirical land use change model and an event-scale, rainfall-runoff model to quantify the impacts of potential land use change on the storm-runoff generation in the Xitiaoxi basin upstream of Taihu Lake watershed. The HEC–HMS rainfall-runoff model is calibrated and validated for 7 storm events in the study area, and the results show good consistency between the simulated and measured hydrographs at the outlet of the basin with Nash–Sutcliff efficiency ranging from 75% to 95%. Then two future land use scenarios for the year 2050 are forecasted using the CLUE-s model based on the land use of 2002: (1) scenario A with an increase in urban area from 9.2% to 17% of the entire watershed and (2) scenario B with an increase from 9.2% to 14%. Finally, the calibrated HEC–HMS model is applied for these future land use scenarios under designed storms with different recurrence intervals to assess the potential land use impacts on the storm-runoff generation. The results indicate that the future land use scenarios are projected to increase the total runoff as well as the peak discharge, and that the magnitude of increment relates to the expansion rate of built-up area. In the case of rainstorms with recurrence intervals of 10, 50 and 100 years, the simulated peak discharges increase by 3.8%, 2.6% and 2.3% under scenario A, and by 2.8%, 1.9% and 1.7% under scenario B, respectively; while the total runoff is projected to increase by 4.7%, 3.4% and 3.0% under scenario A, and by 3.3%, 2.5% and 2.1% under scenario B. It can be concluded that the sensitivity of hydrologic response to land use change tends to increase as the recurrence interval of rainfall events decreases. Additionally, remarkable spatial variations of the land use changes and its impacts can be observed at the subbasin level, and the most sensitive subbasin is closeby the city. The results of this paper can provide useful support for land use planning and management, and the methods applied here have proved a useful tool for land use impact studies. [Copyright &y& Elsevier]

The surface hydrology and diffuse pollution loading is hypothesized based on the unique characteristics under different rainfall types in watersheds with a subtropical monsoon climate. This study evaluated the effects of different rainfall event intensity on surface runoff and diffuse nitrogen loss in a subtropical watershed located in the latitude range between 22.5° north and 25° north in southern China by adapting the hydrological model SWAT (Soil and Water Assessment Tool). The rainfall events were classified into four categories including light rainfall (LR), moderate rainfall (MR), intense rainfall (IR), and extreme rainfall (ER). Our results showed that the ER events had the lowest occurrences of 7 days per year, but they contributed the most to total surface runoff (54.29%) and TN losses (57.63%) in the subtropical watershed researched. Although forests and pastures had a better effect on reducing diffuse pollution, their surface runoff and nitrogen loss were still proved to be serious under ER events. As for the nitrogen loss form, water-soluble nitrogen oxides nitrogen (ON-N) loss was the dominant form of total nitrogen (TN) loss, which accounted for 90% of the total loss in the simulated watershed in the subtropical monsoon climate region. Under LR events, however, nitrate nitrogen (NO3-N) accounted for 74.54% and 55.59% of TN losses from paddy fields and dry lands, respectively. The effects of antecedent soil water content (ASW) on surface runoff and TN loss were higher under ER events. The surface runoff and TN loss in the high-ASW condition were 1.17–3.86 times and 1.34–1.76 times higher, respectively, than in the low-ASW condition. These findings highlighted the important influence of ER events on diffuse pollution and have significant implications for controlling diffuse pollution under different rainfall types. This conclusion proved that extra attention and efforts are required in handling non-point-source pollution in subtropical monsoon watersheds than the watersheds in cooler regions because the natural systems including forest and pastures are no longer effective enough in controlling surface runoff and TN loss during ER. [ABSTRACT FROM AUTHOR]

Consumed CO2 in silicate chemical weathering can be calculated by the chemical composition of the runoff, but trace carbonate weathering and pollutants have a significant impact on the hydrochemical signals. In this study, the chemical composition of runoff of four sub-basins with different trace carbonate contents in strata and land use types of the Xizhijiang River (XZR) basin was measured to investigate the impact of lithology and land use on the chemical runoff as well as estimating CO2 consumed by chemical weathering. Compared with the global rivers, the chemical runoff produced by weathering in the XZR basin with a hot and humid climate has a moderate concentration of total dissolved solids and a relatively higher concentration of dissolved silicon. Agricultural and industrial activities increased the riverine water Cl− concentration, and trace carbonate weathering released a large amount of Ca2+. More intensive chemical weathering in summer weakened the dilution effect of rainwater on runoff ions in the mid-upstream XZR basin. In the sub-basins affected by agricultural and industrial runoff, the ion concentration was significantly higher in the dry season than in the rainy season. The CO2 flux fixed by the chemical weathering is 3.13 × 105 mol km−2 a−1 for the mid-upstream XZR basin, which constitutes a significant geological carbon sink if extrapolated to the whole of South China. [ABSTRACT FROM AUTHOR]

Flood disasters have occurred frequently in recent years, but there is no consensus on the mechanism and influencing factors. Taking the upper reaches of Weihe River Basin as a case in Western China, a soil and water assessment tool (SWAT) model was established to quantitatively simulate the impact of land use and climate change on runoff changes, while 4 extreme land-use scenarios and 24 temperature and precipitation scenarios assumptions were proposed to simulate the response of runoff to land use and climate changes. The SWAT simulation results showed that the sensitivity parameters affecting the model simulation were the CANMX, CN2, SOL_K, CH_N2, and SOL_AWC. The correlation index R2 and the efficiency coefficient ENS of the upper Weihe River were both in the range of 0.75–0.78, the relative error PS between the simulated results and the measured runoff was below 10%, suggesting the good applicability of the SWAT model in this study area. Using the improved SWAT model to simulate the peak runoff (flood) simulation value is generally smaller than the measured value, and the absolute value of the error is less than 6%. The expansion of wasteland increased the runoff by over 90% on average, the expansion of cultivated land increased the runoff by 8% on average, and the expansion of woodland and grassland increased the surface runoff by 6% on average. When the precipitation decreased by 25% and the temperature increased by 22%, the smallest runoff was obtained in the simulation. Accordingly, when the precipitation increased by 25% and the temperature decreased by 22%, the maximum annual runoff was obtained. By decomposing the contribution rate of human activities and climate change to runoff, it showed that the contribution rate of human activities to the reduction of runoff was greater than that of climate change. This study can provide scientific reference for the simulation and prediction of future floods. [ABSTRACT FROM AUTHOR]

River runoff and suspended sediment play a critical role in the chemical, physical, biological processes of Earth's ecosystems. We assessed the temporal changes in runoff and sediment load at both the annual and event scales in the Gushanchuan watershed in the middle reaches of the Yellow River. A total of 330 events, from 1955 to 2018, were selected to evaluate the relationships between rainfall, runoff, and suspended sediment load at the Gaoshiya gauging station. Significant reductions were examined in the maximum runoff peaks, suspended sediment concentration, total runoff, suspended sediment yield, and ratio of event runoff to annual total, whereas the ratio of event sediment yield to annual total remained relatively stable. Hysteresis analysis suggested that the complex loops, anti‐clockwise, and figure‐eight loops accounted for 93.7% of the total events in the watershed. High positive correlations were observed between the flood‐event sediment yield, runoff volume, maximum runoff peaks, and total rainfall amount. The flow‐sediment relationship can be well fitted by the proportional model, and was weaker in 1997–2018 than those in the periods of 1955–1979 and 1980–1996. Runoff during the rising limb of the event significantly contributed to the total runoff and sediment yield. Land use changes and various soil conservation practices were responsible for the decrease in the flood frequency and magnitude. The results of this study provide useful insights into the relationships between rainfall, runoff, and suspended sediment dynamics, and their responses to soil conservation practices. [ABSTRACT FROM AUTHOR]

Variability and availability of water resources under changing environment in a regional scale have been hot topics in recent years, due to the vulnerability of water resources associated with social and economic development. In this paper, four subbasins in the Dongjiang basin with a significant land use change were selected as case study. Runoffs of the four subbasins were simulated using the SCS monthly model to identify the quantitative impacts of land use and climate change. The results showed that (1), in the Dongjiang basin, temperature increased significantly, evaporation and sunlight decreased strongly, while precipitation showed a nonsignificant increase; (2) since the 1980s, land uses in the Dongjiang basin have experienced a significant change with a prominent increase inurbanareas, amoderate increase in farmlands, anda greatdecrease inforest areas; (3) the SCSmonthlymodel performed well in the four subbasins giving that the more significant land use change in each subbasin, the more runoff change correspondingly; (4) overall, runoff change was contributed half and half by climate change and human activities, respectively, in all the subbasins, in which about 20%~30% change was contributed by land use change. [ABSTRACT FROM AUTHOR]

Abstract: This paper analyzes runoff and soil loss in relation to the rainfall regimes and land use changes in a small mountainous watershed in the Three Gorges Area (TGA) of China. Based on 10years of rainfall measurements and K-means clustering, 152 rainfall events were classified into three rainfall regimes. The mean statistical features of different rainfall regimes display a marked difference. Rainfall Regime I is events of medium amounts (31.8mm) and medium duration (1371min). Rainfall Regime II is events with high amounts (54.0mm), long duration (2548min), and an infrequent occurrence. Rainfall Regime III is events of low amount (22.2mm), short duration (494min) and high frequency. Each rainfall regime results in differing levels of runoff and erosion and Rainfall Regime I causes the greatest proportion of accumulated discharge (368.7mm) and soil loss (4283t). In the different rainfall regimes, the values of the mean runoff coefficient and the mean sediment load were ordered as follows: Rainfall Regime II>Rainfall Regime I>Rainfall Regime III. These results suggest that greater attention should be paid to Rainfall Regimes I and II because they had the most erosive effect. In the Wangjiaqiao watershed, the changes in land use primarily affected the paddy fields, where the cropland decreased significantly and the forest and orchards increased by 9.9% and 7.7%, respectively, during 1995–2004. The ANOVA shows land use changes caused significant decreasing trends in the runoff coefficients (P<0.01) and sediment loads (P<0.01). In order, the most sensitive response of runoff and erosion to land use was Rainfall Regime II>Rainfall Regime>Rainfall Regime III. Rainfall characteristics are decisive for the relative importance of different storm runoff generation mechanisms. The land use changes in the study watershed have considerably decreased runoff and soil loss. [Copyright &y& Elsevier]

This study aims to investigate the combined effects of temperature and precipitation on the hydrological processes in a watershed with intensive agricultural land uses during the spring snowmelt period. Temperature, precipitation, soil moisture, frozen soil depth, and discharge were monitored during the freezing and thawing periods in 2014, 2015, and 2016 within the 75 km2 agricultural Heidingzi watershed in northeast China. The results indicated that high autumn rainfall and early precipitation, as well as the corresponding temperature rise, during the stable freezing period, increased the amount of surface water stored in the ice form before the spring runoff. These conditions produced a prolonged and increasing runoff event, and the highest runoff ratio of the ice melt runoff process during the thawing period in 2014. However, low autumn rainfall, dispersed precipitation, and negligible temperature rises during the stable freezing period in 2014–2015 led to a significant but short-term snowmelt runoff during the thawing period in 2015. Because of similar precipitation conditions as in 2014–2015 and a temperature rise event during the freezing period in 2015–2016, the runoff during the thawing period in 2016 was a combination of snow and ice melt; the runoff ratio during the early- and late-melt stages in the maize-dominated drainage region (DR) was the highest with the lowest precipitation. Additionally, the early low rainfall during the thawing period in 2014 increased the direct runoff ratios by 2–13 times for the entire watershed, DRM, and DRP-M, as early rainfall resulted in small soil thaw depth and low water storage. Different land use activities in the agricultural watershed supported the spatial and temporal differences and uncertainties in the spring snow or ice melt runoff generation process. Moreover, snowmelt simulation models can rarely distinguish between ice and snowmelt during spring runoff generation processes, probably leading to high uncertainty in simulating spring runoff response to climate change in seasonal freezing areas. This study reveals the characteristics and causes of snow and ice melt runoff processes in agricultural watersheds that experience seasonal freezing and provides a new perspective for improving the modeling of water generation processes. [ABSTRACT FROM AUTHOR]

Flooding and waterlogging are frequent disasters that pose serious threats to the safety of human lives and infrastructure. We propose a method of estimating the inundation area in urban mountainous zones based on the soil conservation service curve number (SCS-CN) model. Remote sensing data are used to localize parameters and ensure model accuracy, and are combined with topographic maps to determine land-use type, slope, and waterlogged ground. Watershed analysis based on the SCS-CN model is performed to obtain rainfall-runoff data. The inundation area is then estimated from the rainfall data, and the spatial and temporal distribution characteristics of the flood inundation area are analyzed from the perspective of land use. Experimental results from a case study in Mingxi, China, verify the effectiveness of this method for the analysis of flood inundation in urban mountainous areas. [ABSTRACT FROM AUTHOR]

Reasonable allocation of water resources in dryland pastures plays a decisive role in local ecological protection and economic development. Changes in the local climate and vegetation have a direct impact on the local runoff. With Darhan Muminggan Joint Banner (DM Banner) as the study area in China, we made use of the Soil and Water Assessment Tool (SWAT) hydrological model, calibrated and fitted the parameters into the model according to the local meteorological statistics and data on land utilization, soil texture and runoff. After fitting and calibration, we built a SWAT model for arid desert grasslands to simulate and forecast re-distribution of water resources in the study area under changes in the climate and vegetation. This study is expected to provide technical support for reasonable development and utilization of water resources in dryland pastures as well as ecological recovery in Inner Mongolia of China. [ABSTRACT FROM AUTHOR]

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Land-use change has significant impacts on hydrologic processes at the watershed level; thus, quantitative assessment on the impacts of land-use change is vital for basin environment protection and water resources sustainable development. Owing largely to computer and geographical information system (GIS) technology improvements, the distributed hydrological models, which allow describing the temporal variability and spatial distribution of water-balance components, offer an effective approach to quantify the land-use change effects on watershed water quantity. In this study, a soil and water assessment tool model was used to simulate land-use change effects on water quantity in the upper Huaihe River basin in China above the Xixian hydrological controlling station with a catchment area of by the use of temporal three-phase (1980s, 1990s, 2000s) land-use maps, soil type map (1:200,000 scale), and 1980-2008 daily time series of rainfall from the upper Huaihe River basin. Within the model, potential evapotranspiration was computed using the Penman-Monteith method coupled with a simplified plant growth model. On the basis of the simulated time series of daily runoff, land-use change effects on spatio-temporal change patterns of runoff coefficients and runoff modules, the rainfall-runoff relationship, the sensitivity of rainfall-runoff relationship to rainfall for different types of land use, and impact of land-use patterns on rainfall-runoff relationships were investigated. The results revealed that under the same condition of soil texture and terrain slope, the advantage for runoff generation and the sensitivity of rainfall-runoff relationship to rainfall decreased by farmland, paddy field, and woodland. With the same rainfall, the advantage for runoff generation increased by the 1990s, 2000s, and 1980s land-use patterns. The outputs could provide important references for soil and water conservation and river health protection in the upper stream reach of the Huaihe River. [ABSTRACT FROM AUTHOR]

The Laohahe River basin, located in northeastern China, was selected as a case study to quantify the magnitude of changes in land use and land cover (LULC) during the period from the 1970s to the 2010s and its quantitative effects on surface hydrology, based on hydrologic modeling of a distributed Soil and Water Assessment Tool ( SWAT) model and catchment-scale spatial information analyses from remotely sensed data. Land cover maps with 30-m resolution from 1979, 1989, 1999, and 2007, interpreted from Landsat images, were used to analyze LULC changes during the last decades. The observed daily hydro-meteorological data from 1970 to 2006 were divided into four periods: 1970-1979, 1980-1989, 1990-1999, and 2000-2006. The SWAT model was utilized for each period with four LULC scenarios, which were developed by using the four LULC maps. Annual and monthly surface runoff and actual evapotranspiration (AET) were selected as important hydrologic elements to indicate the hydrologic response to LULC changes. The results revealed that distinct land cover changes occurred in the basin; the most important change was the conversion among vegetation cover classes of cropland, forest land, and grassland. Surface runoff always decreased as the LULC scenarios changed from 1976 to 2007 during all periods, but AET did not change regularly following the present LULC changes. Multiple regression equations between quantitative changes of LULC and hydrologic elements were developed. The equations indicated that the changes in three vegetation cover classes of grassland, cropland, and forest areas significantly affected hydrological elements and the increases of vegetation cover class areas all led to decreases in surface runoff and increases in AET. Moreover, given the same quantitative area change, the effects of cropland on hydrologic elements were the strongest, the effects of forest land were the second strongest, and the effects of grassland were the third. The effects of LULC changes on the seasonal distribution of hydrologic elements were also investigated. The results demonstrated that LULC changes have less influence on surface runoff and AET in nonflood seasons, but more influence in flood seasons, especially in July, August, and September, when the crops grow best. The results of this study improved the understanding of hydrologic responses to LULC changes and provided needed knowledge for agricultural decisions and the management of land use and integrated water resources. [ABSTRACT FROM AUTHOR]

The Fenhe River is the second largest tributary of the Yellow River in China. Climatic variation and human activities have impacted the runoff significantly in the Fenhe River in recent decades. In this study, the runoff trend from 1957 to 2010 was analyzed and the impacts of climatic variation and human activities on runoff were attributed by the climate elasticity method and hydrological modeling method. The observed annual runoff decreased significantly ( P < 0.05) during the past 54 years in the Fenhe River basin. A change point was identified around the year 1979 for the annual runoff series by the Mann-Kendall test. The observed average annual runoff in the Period II (from 1980 to 2010) decreased by 24.94 mm compared with the Period I (from 1957 to 1979). The attribution results show that the average annual amount of water diversion from the river in the Period II increased significantly by 7.88 mm compared with the Period I, accounting for 31.6 % of the total decrease in the observed annual runoff. In addition, other human activities such as land use and cover change led to the decrease in annual runoff by 6.31 mm from the climate elasticity method and 6.92 mm from the hydrological modeling method, which accounting for 23.8 and 27.7 % of the total decrease in the observed annual runoff, respectively. Therefore, human activities together were responsible for 55.4 % of the total observed runoff reduction estimated by the climate elasticity method and for 59.3 % estimated by the hydrological modeling method. Climatic variation such as changes in precipitation and evapotranspiration led to the decrease in runoff by 10.14 and 10.75 mm from the two methods, accounting for 40.7 and 44.6 % of the total observed runoff reduction. Therefore, human activities were the main driving factor for the runoff decrease in the Fenhe River basin. [ABSTRACT FROM AUTHOR]

Climate, land use and human activity have an impact on the Qingshui River in Chongli County. The Soil and Water Assessment Tool (SWAT) was used to separately analyze the contributions of climate, land use and direct human activity on the discharge variations. The results indicated that human activity had been the dominant factor for the discharge decrease, while climate and land use change had a positive influence on the discharge increase. The contributions of these three factors were −56.24%, 38.59% and 5.17%, respectively. Moreover, on the seasonal scale, the impact of those factors was consistent with their impact on the annual scale. Human activity was the main factor for discharge decrease in the summer, the contribution accounting for −77.13%. Due to the over-extraction of groundwater for irrigation and use in the mining industry, the discharge showed a decreasing tendency, which has the potential to place stress on sustainable water use in the future. The result of the study may contribute to the optimization of water resource allocation and management. [ABSTRACT FROM AUTHOR]

Purpose: It is critical to understand the effect of manure application on the availability of phosphorus (P) and the potential environmental contamination by runoff and leaching. However, previous studies generally focused on cultivated soil layer in single cropping systems. The aim of this study was to evaluate the effect of manure application on soil P forms and quantities to the 200 cm depth in a Chinese alkaline Cambisol in different cropping systems and the potential environmental implications. Materials and methods: The sampling site, Shunyi District, is located in the peri-urban area of Beijing in the North China Plain, where large quantities of manure generated from intensive animal operations have been applied to agricultural fields. A field survey was carried out before sampling to identify soil sampling sites with long-term manure application and an adjacent area receiving no manure used for the same crop production. Soil samples from three cropping systems (vegetables, cereals, and trees) were vertically collected to a depth of 200 cm with the following depth increments: 0-20, 20-60, 60-90, 90-120, 120-160 and 160-200 cm. Soil samples were analyzed for plant-available P (Olsen P) and various P fractions by sequential P fractionation. Degree of P saturation (DPS) was also determined. Results and discussion: Soil calcium bound P was the most abundant P fraction, followed by the residual P. Organic P only accounted for less than 5 % of total P in most of the soils. Manure application increased the levels of inorganic P (Pi), with higher proportions of Pi in labile forms than stable forms. After manure application for 8-15 year, available P (Olsen P) and DPS values of the 0-20 cm layer in all sites exceeded the threshold for Olsen P (60 mg kg) and DPS (30 %) and the risk of P loss by runoff is expected to significantly increase. The DPS values were generally lower than 30 % below 20 cm, indicating a minimal risk of P loss via leaching from deeper soil. Conclusions: The results indicated that in typical peri-urban areas of the North China Plain, the on-going practice of manure application not only increased the size of each of the labile and non-labile P pools, but also caused a shift in the relative sizes of the different pools, regardless of the cropping systems. However, contrary to what was expected, soil P loss through surface runoff would be a greater concern than leaching following long-term manure amendment. [ABSTRACT FROM AUTHOR]

The article presents a study on the impact of land use on distributed hydrological processes in a wetland-based ecosystem in Jilin, China. The study used Water and Energy Transfer between Soil, Plants and the Atmosphere under quasi-Steady-State (WetSpass) and MODFLOW model to simulate the water balance components of distributed recharge, runoff and evapotranspiration (ET). The study found that ET-limiting land/water resources are critical factors for the preservation of wetland-based ecosystem.

The article presents a study which determines the role of Xinanjiang model in flood forecasting in China. It states that the model is a rainfall-runoff model that is widely used in humid, semi-humid, and dry area in the country for flood forecasting. Accordingly, Xinanjiang model is coupled by kinematic wave method based on a digital drainage network. It notes that the main advantage of the model is that it can determine the spatial distribution of soil moisture storage. Moreover, topography and land use data are used by kinematic wave of Xinanjiang model to simulate runoff and overland flow routing. The Kinematic wave of the model was also used as overland flow routing model for the rainfall-runoff model grid.

To study the response of runoff to extreme changes in land use, the Soil and Water Assessment Tool (SWAT) model was used to construct historical, extreme, and future scenarios for several major landscape types in a permafrost region of northeastern China. The results show that the SWAT model is applicable in the Tahe River Basin; forestlands, shrublands, wetlands, and grasslands are the main land-use types in this basin, and the transfers among them from 1980–2015 have impacted runoff by less than 5%. Under extreme land use-change scenarios, the simulated runoff decreased from grasslands, to wetlands, shrublands, and finally, forestlands. The conversion of extreme land-use scenarios produces different hydrological effects. When forestland is converted to grassland, runoff increases by 25.32%, when forestland is converted to wetland, runoff increases by 13.34%, and the conversion of shrubland to forestland reduces runoff by 13.25%. In addition, the sensitivity of runoff to different land-use changes was much greater during flood seasons than in dry seasons. Compared to the reference year of 2015, the annual simulated runoff under the two future land-use scenarios (shrublands to forestlands and shrublands to wetland) was less. Also, both future land-use scenarios showed effects to decrease flooding and increased dryness, This study provided important insight into the integrated management of land use and water resources in the Tahe River Basin and the permafrost region of northeastern China. [ABSTRACT FROM AUTHOR]

The effects of land-use changes on the runoff process in the midstream plain of this arid inland river basin are a key factor in the rational allocation of water resources to the middle and lower reaches. The question is whether and by how much increasingly heavy land use impacts the hydrological processes in such an arid inland river basin. The catchment of the Heihe River, one of the largest inland rivers in the arid region of northwest China, was chosen to investigate the hydrological responses to hind-use change. Flow duration curves were used to detect trends and variations in runoff between the upper and lower reaches. Relationships among precipitation, upstream runoff, and hydrological variables were identified to distinguish the effects of climatic changes and upstream runoff changes on middle and downstream runoff processes. The quantitative relation between midstream cultivated land use and various parameters of downstream runoff processes were analysed using the four periods of land-use data since 1956. The Volterra numerical function relation of the hydrological non-linear system response was utilized to develop a multifactor hydrological response simulation model based on the three factors of precipitation, upstream runoff, and cultivated land area. The results showed that, since 1967, the medium- and high-coverage natural grassland area in the midstream region has decreased by 80.1%, and the downstream runoff has declined by 27.32% due to the continuous expansion of the cultivated land area. The contribution of cultivated land expansion to the impact on the annual total runoff is 14-31%, on the annual, spring and winter base flow it is 44-75%, and on spring and winter discharge it is 23-64%. Once the water conservation plan dominated by kind-use structural adjustments is implemented over the next 5 years, the mean annual discharge in the lower reach could increase by 8.98% and the spring discharge by 26.28%. This will significantly alleviate the imbalance between water supply and demand in both its quantity and temporal distribution in the middle and lower reaches. [ABSTRACT FROM AUTHOR]

Large areas of traditional slope cropland were recently converted to other land-use types in the semiarid Loess Plateau of China. In this study, we selected four representative conversion options of slope croplands, i.e., pastureland rotated with cropland (cultivated with Medicago sativa L. and rotated with Triticum aestivum L.), shrubland and woodland (afforested with Hippophae rhamnoides L. and Pinus tabulaeformis), and grassland (native herbage Stipa breviflora) to study the effect of land-use conversion by comparing with traditional cropland. Compared with slope cropland, the relative effects of different conversion options on surface runoff and soil erosion were assessed over a 14-year measurement period. Observations showed that distinct features and consequences of vegetation succession were found among the conversion options. Plots of shrubland had the highest vegetation coverage with dense undergrowth; natural herbaceous and subshrub species gradually spread into plots of grassland resulting in higher vegetation cover. Neither bushes nor herbs colonized the plots of Pinus tabulaeformis, which resulted in a higher percentage of bare soil. Significant differences in runoff generation, sediment yield and conservation efficiencies among the selected conversion options were detected through an analyses of variance (ANOVA). Compared with cropland, total runoff and sediment decreased by 65 per cent and 95 per cent in shrubland, 41 percent and 92.5 per cent in grassland, 18 per cent and 77 per cent in woodland, and 12 per cent and 58 per cent in pastureland, respectively. The ranking of soil and water conservation efficiencies was shrubland > grassland > woodland > pastureland > cropland. Based on the effectiveness of soil and water conservation, shrubland and grassland are highly recommended as promising options for cropland conversion projects. However, pastureland and woodland are not suggested as potential options for slope-cropland conversion because of low soil and water conservation in the long term. [ABSTRACT FROM AUTHOR]

The article presents abstracts of several studies on environmental geochemistry. Some of the abstracts presented include "Biogeochemical Cycling of Nutrients in Karstic Catchments, Southwestern China: Linkages to Changes of Eco-Environments," by Congqiang Liu and "Emerging Organic Contamination in China," by Guibin Jiang and colleagues.

In the Shixia small watershed, twenty experimental plots and two monitoring channels, the residential area and livestock areas were used to monitor the flow, runoff and erosion. Nitrogen and phosphorous concentrations associated with various land uses were analyzed at the same time. The results are presented as follows: (1) TP, TN and COD concentrations of runoff samples in the residential area and livestock areas are nearly 10 times those in other land-use areas. High nutrient loads are associated with village land use, which is due to unsuitable livestock rising. These areas should be treated as the critical areas of non-point source pollution. (2) Different land-use influences intensity the loss of nutrients, especially slope tillings in agricultural land. The amount of nutrient loss from agricultural land per unit is highest, that from forestry is intermediate and that from pastures is lowest. However, in consideration of the variability of land-use areas, agricultural land contributes the greatest to TP and forestry land to TN. (3) The concentrations of TN and TP in sediments from gangues are highest, those in forestry land are intermediate, and those in agricultural land are lowest. Nutrient loss from hilly areas is much greater than from mountainous areas. [ABSTRACT FROM AUTHOR]