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Although it is important in hydrological cycles, catchment water storage dynamics is still not fully understood because it is affected by multiple drivers simultaneously and is difficult to be estimated using field hydrometric observations and hydrological models. Taking the headwater of Baiyang Lake, China as an example, this study employed a spectral approach to illustrate how catchment water storage was influenced by rainfall and vegetation, and how water storage modulated streamflow for the period of 1982–2015. The competence of the spectral approach in characterizing causality was verified and a more holistic understanding of hydrological cycles was gained. Results showed that under different climatic phases (wet/dry), catchment water storage dynamics were controlled by different factors and dominant streamflow generation mechanisms were not invariant. In the wet phase, catchment water storage dynamics was determined by rainfall. And groundwater flow was the most important part of streamflow, followed by subsurface flow and surface flow. Nevertheless, in the dry phase, catchment water storage dynamics was modulated by evapotranspiration. And the surface flow was the most important part of streamflow, followed by subsurface flow and groundwater flow. The land use change induced by human activities could alter the streamflow sensitivity to rainfall, but could not cause fundamental changes to hydrological cycles. We concluded that the spectral approach can be an effective supplement to the experimental methods and their integration can provide systematic insights into hydrological cycles in the study area and other watershed systems.

In Belgium, IWVA uses managed aquifer recharge (MAR) to recharge the aquifer with treated wastewater generated from the communities to sustain the potable water supply on the Belgian coast. This MAR facility is faced with a challenge of reduced infiltration rates during the winter season when pond water temperatures near 4°C. This study involves the identification of the predominant factor influencing the rate of infiltration through the pond bed. Several factors, including pumping rates, natural recharge, tidal influences of the North Sea and pond‐water temperature, were identified as potential causes for variation of the recharge rate. Correlation statistics and linear regression analysis were used to determine the sensitivity of the infiltration rate to the aforementioned factors. Two groundwater flow models were developed in visual MODFLOW to simulate the water movement under the pond bed and to obtain the differences in flux to track the effects of variation of hydraulic conductivity during the two seasons. A 32% reduction in vertical hydraulic gradient in the top portion of the aquifer was observed in winter, causing the recharge rates to fluctuate. Results showed that water temperature caused a 30% increase in hydraulic conductivity in summer as compared with winter and has the maximum impact on infiltration rate. Cyclic variations in water viscosity, occurring because of seasonal temperature changes, influence the saturated hydraulic conductivity of the pond bed. Results from the models confirm the impact on infiltration rate by temperature‐influenced hydraulic conductivity.

The temporal and spatial distributions of regional irrigation water productivity (RIWP) are crucial for making decisions related to agriculture, especially in arid irrigated areas with complex cropping patterns. Thus, in this study, we developed a new RIWP model for an irrigated agricultural area with complex cropping patterns. The model couples the irrigation- and drainage-driven soil water and salinity dynamics and shallow groundwater movement in order to quantify the temporal and spatial distributions of the target hydrological and biophysical variables. We divided the study area into 1 km × 1 km hydrological response units (HRUs). In each HRU, we considered four land use types: sunflower fields, wheat fields, maize fields, and uncultivated lands (bare soil). We coupled the regional soil hydrological processes and groundwater flow by taking a weighted average of the water exchange between unsaturated soil and groundwater under different land use types. The RIWP model was calibrated and validated using 8 years of hydrological variables obtained from regional observation sites in a typical arid irrigation area in North China, the Hetao Irrigation District. The model simulated soil moisture and salinity reasonably well as well as groundwater table depths and salinity. However, overestimations of groundwater discharge were detected in both the calibration and validation due to the assumption of well-operated drainage ditch conditions; regional evapotranspiration (ET) was reasonably estimated, whereas ET in the uncultivated area was slightly underestimated in the RIWP model. A sensitivity analysis indicated that the soil evaporation coefficient and the specific yield were the key parameters for the RIWP simulation. The results showed that the RIWP decreased from maize to sunflower to wheat from 2006 to 2013. It was also found that the maximum RIWP was reached when the groundwater table depth was between 2 and 4 m, regardless of the irrigation water depth applied. This implies the importance of groundwater table control on the RIWP. Overall, our distributed RIWP model can effectively simulate the temporal and spatial distribution of the RIWP and provide critical water allocation suggestions for decision-makers.

The Hueco Bolson aquifer is a binational aquifer shared by the United States of America (USA) and Mexico that is strongly interconnected with the transboundary river, Rio Grande/Rio Bravo. Limited recharge, increasing urbanization, and intensified agriculture have resulted in the over-drafting of groundwater resources and stressed the aquifer, threatening its sustainability if mitigation actions are not taken soon. Research indicates that the aquifer’s hydraulic gradients and flow directions have changed due to the high groundwater withdrawal rates from the two major cities—El Paso (USA) and Ciudad Juarez (Mexico). This paper presents a comprehensive overview of the Hueco Bolson aquifer modeling history and makes a case for future modeling and binational engagement efforts. First, we discuss the evolution of groundwater modeling for Hueco Bolson from the past to recent times. Second, we discuss the main water management issues in the area, including water quality and quantity, stakeholders’ participation, and climate change. To address the challenges of holistic water management, we propose developing a graphical quantitative modeling framework (e.g., system model and Bayesian belief network) to include experts’ opinions and enhance stakeholders’ participation in the model. Though the insights are based on a case study of Hueco Bolson, the approaches discussed in this study can provide new strategies to overcome the challenges of managing a transboundary aquifer.

When allocating water resources, stakeholders (such as water departments, agricultural sector actors, and farmers) aim to maximize their benefits. This leads to conflicts between water savings, food security, and profit growth, causing major challenges for water managers. A hydro-economic model was developed to alleviate groundwater sustainability, food security, and economic growth (GFE) conflicts through crop pattern optimization. This model combines groundwater, agronomic, and economic sub-models to simulate spatiotemporal variations in groundwater level, irrigation requirement, crop production, and net profit. The NSGA-II algorithm was used to maximize net profits while minimizing groundwater extraction and food reduction through crop pattern optimization in irrigation areas and under crop production constraints. Then, using the Baoding Plain as the study area, three scenarios with no external water supply and nine scenarios with an external water supply of 0.3, 0.6, and 0.9 km

With growing competition for freshwater by industrialization and urbanization, brackish water irrigation has been increasingly used for agricultural production. One of major concerns is the accumulation of salt and its impacts on soil properties and crop yield. If properly managed, alternate irrigation with brackish and freshwater might alleviate the adverse impacts of salt on soil physicochemical properties and plant growth. To exploit proper alternate irrigation to minimize such impacts, a maize pot experiment was conducted at three stages (seedling, jointing and tasseling, and after tasseling) with three alternate irrigation methods (BFF: brackish-fresh-fresh, FBF: fresh-brackish-fresh, and FFB: fresh-fresh-brackish) and with three salinities (1.69, 4.81, and 7.94 dS m-1), respectively. The results show that compared to freshwater irrigation, alternate irrigation with high-salinity brackish water increased soil electrical conductivity by 4.1% to 207.4% and reduced soil infiltration rate by 19.2% to 51.9%. The adverse impacts were more prominent in FBF and FFB than in BFF due to the higher proportions of brackish water in FBF and FFB. High-salinity brackish water also caused salt stress on maize growth and decreased evapotranspiration, relative water content, intrinsic water use efficiency, and electron transport rate by 6.6% to 30.6%, 2.1% to 10.2%, 7.3% to 17.9%, and 7.2% to 39.6%, respectively, leading to reduced growth and productivity. The salt stress was more pronounced in BFF and FBF than in FFB because maize is more salt-sensitive during the vegetative stage. Overall, brackish water irrigation at the jointing and tasseling stage (FBF) caused the most severe impacts on both soil and maize, so freshwater is advocated at this stage. In BFF, due to sufficient freshwater irrigation at later stages, slightly saline irrigation can be applied at the seedling stage without evident adverse effects. Higher-salinity brackish water was used successfully in the after-tasseling stage (FFB), although salt leaching by off-season rainfall was needed after harvest for sustainable production. Keywords: Crop yield, Saline water, Salt stress, Soil salinity, Water use efficiency.

Interactions between groundwater mounds caused by a geologic layer contrast affect the efficiency of managed aquifer recharge in arid areas. However, research has rarely examined the roles of groundwater mounding size variations on soil water dynamics in a stratified vadose zone in response to a sustained infiltration source. Numerical experiments were conducted on a two‐dimensional vertical‐section domain using HYDRUS software to simulate the behaviours of two adjacent (upper and lower) groundwater mounds underlying an infiltration basin subjected to clay loam and sandy alternately‐layered soil profiles. The model successfully predicted the volume and extent of perched water and approximated vertical travel times during events generating downward fluxes from the surface injection. The response time of the mounding width (lateral extension) to the surface injection was delayed as compared to that of the mounding height (vertical extension), especially for the lower water mound. The mounding heights and widths show a strongly positive correlation with the infiltration rates of both high‐ and low‐permeability layers where the injected water mounded, while the water storage amounts in the high‐ and low‐permeability layers were governed by the mounding height and width, respectively. Exploratory simulations were then employed to assess the dependence of groundwater mounding behaviours and recharge performances on surface injection strategies. Results suggest that, by reducing injection rate or shortening injection duration, the near‐term fraction of the surface injection converted to deep recharge is likely to be increased due to the narrowed groundwater mounding size, which would be limited by the water‐retarding effect of layer contrasts. This study has important implications for predicting and understanding multilayered groundwater mounding behaviours and associated water mass balance under the geologic stratification, and is expected to aid in optimizing the infiltration basin operation for aquifer recharge.

As more aquifer storage and recovery (ASR) systems are employed for management of water resources, the skillful operation of multiwell ASR systems has become very important to improve their performance. In this study, we developed MODFLOW and MT3DMS models to simulate a multiwell ASR system in a synthetic aquifer to assess effects of hydrogeological and operational factors on the performance of the multiwell ASR system. We evaluated a simplified (dual well) ASR system in comparison with complex system (three-, four-, five-, and seven-well systems). Recovery and energy efficiencies were calculated using the model simulations. Factors such as higher hydraulic conductivity and longitudinal dispersivity significantly reduced the recovery and energy efficiencies of the system. In contrast, increasing the volume of recharged water increased the recovery efficiency; however, the energy efficiency was reduced. Recovery and energy efficiencies also plummet when there is an increase in the underlying regional gradient and the designed storage duration. Operating the system multiple times can yield higher volume of potable water, but the energy efficiency may not vary significantly after the second operating cycle. Single-well systems and multiwell systems exhibit similar responses to changes in physical factors, although operational factors have a more pronounced effect on the multiwell systems. One of the major findings was that fewer wells in a multiwell ASR system can yield higher volume of potable water and better output with respect to the electrical power being consumed. The results provide design engineers with guidelines for optimizing performance of the multiwell ASR systems.

Understanding groundwater storage variations as a result of effects from both the vadose zone and the river is of critical importance in the hydraulically connected surface‐subsurface system. In this study, we present a novel Bidirectional Exchange Scheme in Surface and Subsurface (BE3S) that represents bidirectional exchanges between the vadose zone, phreatic aquifer, and river. The approach enables explicit representations of each flow regime while conserving mass, and successfully yields solutions of the coupled system for multiple temporal resolutions. We test the scheme by comparing the BE3S‐derived outputs against other models and corresponding observational data. We apply the scheme to simulate hydrologic states in a reach of the Brazos River in Southeast Texas, such as soil moisture content, groundwater level, and river stage as well as net subsurface discharge fluxes. Good agreements between the simulated and observed data for all the components show the suitability of the proposed scheme in modeling the bidirectional flows and exchanges. We also assess how the bidirectional hydrologic exchanges are affected by adjacent flow domains. We find that vertical percolation is significantly affected by unsaturated soil thickness, resulting in the spatial variability of vertical percolation across sloping topography. Hilltop‐to‐valley convergent groundwater flow is also found to impede vertical percolation in river valleys due to shallow water table while facilitating percolation in the hilltops. The capability of the presented scheme that accounts for the topographically driven lateral groundwater flow and drainage dynamics provides the potential to enhance the representation of the surface‐subsurface system in Earth System Models (ESMs).

Inflow and infiltration (I/I) is a common problem in sanitary sewer systems. The I/I rate is also considered to be an important indicator of the operational and structural condition of the sewer system. Situation awareness in sanitary sewer systems requires accurate wastewater-flow information at a fine spatiotemporal scale. This study aims to develop artificial intelligence (AI)-based models (adaptive neurofuzzy inference system (ANFIS) and multilayer perceptron neural network (MLPNN)) and to compare their performance for identifying the potential inflow and infiltration of the sanitary sewer subcatchment of two pumping stations. We tested the performance of these AI models by using data gathered from two pumping stations through a supervisory control and data acquisition (SCADA) system. As a result, these two AI models produced similar inflow and infiltration patterns-both subcatchments experienced inflow and infiltration. On the other hand, the ANFIS had overall higher performance than that of the MLPNN model for modelling the I/I situation for the catchments. The results of the research can be used to support spatial decision making in sewer system maintenance.

This paper examines the coupled effects of weather condition, crop coverage change, and regional water management (i.e., releases from Caballo Reservoir) on hydrologic characteristics of Rincon Valley (2466 km2), a semi-arid agricultural area in New Mexico, U.S.A., using Soil and Water Assessment Tool (SWAT). The model simulates the vertical water budget and horizontal water transfers during the period 1994–2013, incorporating irrigation of fourteen crops in normal (2008) and dry (2011) years to evaluate the hydrologic impacts of cropping change as a drought-adaptive water management strategy. It was calibrated (2000–2002) and validated (2003–2005) using daily-observed streamflow data. Furthermore, evapotranspiration, diversion and irrigation water volume were verified for the period of 2000–2005 using monthly crop irrigation requirement data and canal discharge data. Results demonstrate the significant role of surface water infiltration, providing approximately 18% of the average annual groundwater recharge during the irrigation season. Watershed scale evapotranspiration (ET) and return flows for the irrigation season were estimated to be 23% and 1% higher than those for the non-irrigation season, respectively. For irrigation units, the ratio of ET to combined precipitation and irrigation water for the dry year was 5% higher than the normal year whereas surface runoff, soil water storage, and groundwater recharge were 7%, 17%, and 39% lower than the normal year, respectively. High groundwater recharge occurs in the hydrologic response units (HRU) where corn and cotton are planted on silty clay loam soil. The Alfalfa acreage (i.e., the largest water user) was reduced by 15% while the cotton acreage was increased by 13% in order to adapt to lower water availability during the dry year. Quantitative understanding of the hydrologic fluxes in the Rincon Valley’s irrigated agricultural area illuminates adaptive land and water management to buffer the adverse impacts of prolonged droughts.

Field experiments were conducted to evaluate the impacts of graywater irrigation with and without soil conditioning with mulching on cotton growth and soil properties in El Paso, Texas, USA. Treatments included in the study were: freshwater irrigation without soil conditioning (control, treatment T0), freshwater irrigation with soil conditioning (treatment T1), graywater irrigation without soil conditioning (treatment T2) and with soil conditioning (treatment T3) with four replications. The pH, sodium absorption ratio (SAR) and electrical conductivity (EC) values of the graywater used in the study were 8.19, 16.0 and 1.54 dS/cm respectively. Results showed that graywater irrigation did not have significant impacts on cotton growth and lint yield. Soil conditioning with mulch increased cotton yield significantly (p < 0.05) compared with non-mulching regardless of water types. Graywater irrigation increased soil pH values significantly in the surface depth (0–15 cm), however, it did not have significant effects at greater depths (>15 cm). Significantly higher salinity and sodicity were observed in the upper 30 cm depths in the graywater irrigated mulched soils, while no changes were detected at greater depths (30–45 and 45–60 cm).

Mountainous areas are characterized by steep slopes and rocky landforms, with hydrological conditions varying rapidly from upstream to downstream, creating variable interactions between groundwater and surface water. In this study, mechanisms of groundwatersurface water interactions within a headwater catchment of the North China Plain were assessed along the stream length and during different seasons, using hydrochemical and stable isotope data, and groundwater residence times estimated using chlorofluorocarbons. These tracers indicate that the river is gaining, due to groundwater discharge in the headwater catchment both in the dry and rainy seasons. Residence time estimation of groundwater using chlorofluorocarbons data reveals that groundwater flow in the shallow sedimentary aquifer is dominated by the binary mixing of water approximating a piston flow model along 2 flow paths: old water, carried by a regional flow system along the direction of river flow, along with young water, which enters the river through local flow systems from hilly areas adjacent to the river valley (particularly during the rainy season). The larger mixing ratio of young water from lateral groundwater recharge and return flow of irrigation during the rainy season result in higher ion concentrations in groundwater than in the dry season. The binary mixing model showed that the ratio of young water versus total groundwater ranged from 0.88 to 0.22 and 1.0 to 0.74 in the upper and lower reaches, respectively. In the middle reach, meandering stream morphology allows some loss of river water back into the aquifer, leading to increasing estimates of the ratio of young water (from 0.22 to 1). This is also explained by declining groundwater levels near the river, due to groundwater extraction for agricultural irrigation. The switch from a greater predominance of regional flow in the dry season, to more localized groundwater flow paths in the wet season is an important groundwatersurface water

The Wozeka–Gidole road in Ethiopia experiences frequent slope failure and triggered during road construction. This study identified the actually failed slope to verify numerical results of both limit equilibrium method (LEM) and finite element method (FEM) with the actually failed slope. Modeling of the actually failed slope with the FEM-based PLAXIS software and LEM-based SLOPE/W software had been used to calculate the factor of safety (FOS). The comparative study of the LE methods shows that The Bishop, Janbu, Morgenstern-Price, GLE and Spencer methods yield in most cases identical FOS for circular slip surface. However, the ordinary method may underestimate the FOS. All LE methods, except the Ordinary methods, estimate higher FOS than FE analysis in PLAXIS. Numerical results of both FEM and LEM verify instability of the slope. In general, the model provides the possible major causes of slope instability and their possible remedial measures in the study area.

A constrained total water-use policy has been implemented to maintain sustainable water supply in some water shortage areas. Managing a constrained water-use quota (T) in water allocation is a chal...

Study region: The Gulf Coast and Carrizo-Wilcox aquifer systems in the Gulf Coastal Plains of Texas. Study focus: Aquifer storage and recovery is a water storage alternative that is underutilized in Texas, a state with both long periods of drought and high intensity storms. Future water storage plans in Texas almost exclusively rely on surface reservoirs, subject to high evaporative losses. This study seeks to identify sites where aquifer storage and recovery (ASR) may be successful, especially in recovery of injected waters, by analyzing publicly-available hydrogeologic data. Transmissivity, hydraulic gradient, well density, depth to aquifer, and depth to groundwater are used in a GIS-based index to determine feasibility of implementing an ASR system in the Gulf Coast and Carrizo-Wilcox aquifer systems. New hydrological insights for the region: Large regions of the central and northern Gulf Coast and the central and southern Carrizo-Wilcox aquifer systems are expected to be hydrologically feasible regions for ASR. Corpus Christi, Victoria, San Antonio, Bryan, and College Station are identified as possible cities where ASR would be a useful water storage strategy. Keywords: Aquifer storage and recovery (ASR), GIS, Gulf coast, Carrizo-Wilcox, Managed aquifer recharge (MAR)

The phenomenon of rocky desertification is obvious in karst plateau of Guizhou, China, and the distribution area of slight–medium–severe rocky desertification is very large in Zhenfeng–Guanling–Huajiang, Guizhou. To explore the cause of formation and development of rocky desertification in the region, the karst development mechanism and characteristics were studied by the method of indoor dissolution test and microscopic analysis. The results show that the dissolution and karst features of carbonate rocks are closely related to geological structure, hydrogeological conditions, and lithology. The dissolution rate is the most affected by the chemical composition and mineral composition, followed by the pore structure and the particle feature. The dissolution rate of carbonate is in positive proportion with the calcite content, while it decreases with increasing content of dolomite. In the same chemical composition, the rock with the finer grains has a faster surface dissolution rate. In addition, the erosion amount will change with the pore aperture and connectivity. Karst morphology is mainly affected by the microstructure and mineral assemblage characteristics of carbonate rocks. In this rocky desertification area, bare rock over a large area will be further eroded, which will form the stone bud, stone forest. At the same time, the hydrodynamic effect of groundwater will erode the rock deeply, and the depression, karst funnel, or deep valley will appear gradually.

The temporal and spatial distribution of regional irrigation water productivity (RIWP) is crucial for making agricultural related decisions, especially in arid irrigated areas with complex cropping patterns. Thus, we developed a new RIWP model for an irrigated agricultural area with complex cropping patterns. The model couples the irrigation and drainage driven soil water and salinity dynamics and shallow groundwater movement, to quantify the temporal and spatial distributions of the target hydrological and biophysical variables. We divided the study area into 1 km×1 km hydrological response units (HRUs). In each HRU, we considered four land-use types: sunflower fields, wheat fields, maize fields and uncultivated lands. And we coupled the regional soil hydrological processes and groundwater flow by taking a weighted average of the water exchange between unsaturated soil and groundwater under different land-use types. The RIWP model was calibrated and validated using eight years of hydrological variables obtained from regional observation sites in a typical arid irrigation area of North China, Hetao Irrigation District. The model reasonably well simulated soil moisture and salinity, groundwater table depths, salinity, and discharge, and regional evapotranspiration. Sensitivity analysis indicates that soil evaporation coefficient and specific yield are the key parameters for RIWP simulation. The results showed that, from 2006 to 2013, RIWP decreased from maize to sunflower to wheat. It was found that the maximum RIWP can be reached when groundwater table depth is in the range of 2 m to 4 m, regardless of irrigation water depths. This implies the importance of groundwater table control on RIWP. Overall, our distributed RIWP model can effectively simulate the temporal and spatial distribution of RIWP and provide critical water allocation suggestions for decision makers.

Karez system is considered as the global human heritage since it is not only a traditional water supply system of exploiting groundwater, but also it reflects the culture, socio-economy, and history of the ancient civilizations that had utilized them for thousands of years in arid and semi-arid regions of the world. However, with the explosive population growth and rapid development of pumping technology in the last century, the karezes dried up or were abandoned as pumping wells lower the groundwater table. This poses a dilemma to policy makers whether to facilitate large-scale utilization of pumping well technology over karez system and treat karez as a cultural heritage which is non-functional for food production, or to keep using and preserving the karez system as a sustainable way of groundwater management as part of the integrated water supply systems in the arid regions. In this paper, we reviewed the historical, socio-economic, and cultural importance of karezes in the arid regions. We also discussed the distribution of karezes in the world, their unique geographical characteristics, technological advantages and limitations. We observed that the karez system is not only economically robust over the long term, but also a viable water supply technique for irrigation and domestic uses. The karezes should be protected as indigenous human heritage, and at the same time, they can be utilized as a sustainable way of water resources management in the arid regions to enhance water resiliency under changing environment.

Water-saving technologies have long been seen as an effective method to reduce irrigation water use and alleviate regional water shortage. However, growing reports of more severe water shortage and increasing application of water-saving technologies across the world have necessitated reassessment of agricultural water-saving. This study develops a simple method based on satellite-based ET partitions to estimate water withdrawal, water consumption and return flow from the 1980s to 2010s, and quantifies water-savings across globe and four hot-spot irrigated areas at both field and regional scales based on water accounting framework. The results show that global irrigation water flows keep increasing from the 1980s to 2010s, with over 50% increase from the expansion in irrigated lands. While water-saving technologies are found mainly applied in originally old irrigated lands, traditional flooding irrigation is still dominant in newly-developed irrigated lands. Non-beneficial water consumption (soil evaporation) is effectively reduced by water-saving technologies, but return flow has increased at the same time. At field scale, water-saving technologies fail to save water because the accumulated increased return flow is more than the accumulated decreased non-beneficial water consumption. At regional scale, however, water is saved because the return flow percolated to fresh aquifers is seen as beneficial rather than loss. At the same time, the accumulated increase of beneficial water consumption (crop transpiration) exceeds regional water savings, which explains the paradox between wide application of water-saving technologies and more severe regional water shortage. This study provides key new evidence for the paradox of irrigation efficiency and helps reconsidering water-saving technologies and their impacts on regional water resources.

Recently, canopy transpiration (Ec) has been often estimated by xylem sap-flow measurements. However, there is a significant time lag between sap flow measured at the base of the stem and canopy transpiration due to the capacitive exchange between the transpiration stream and stem water storage. Significant errors will be introduced in canopy conductance (gc) and canopy transpiration estimation if the time lag is neglected. In this study, a cross-correlation analysis was used to quantify the time lag, and the sap flow-based transpiration was measured to parameterize Jarvis-type models of gc and thus to simulate Ec of Populus cathayana using the Penman–Monteith equation. The results indicate that solar radiation (Rs) and vapor pressure deficit (VPD) are not fully coincident with sap flow and have an obvious lag effect; the sap flow lags behind Rs and precedes VPD, and there is a 1-h time shift between Ec and sap flow in the 30-min interval data set. A parameterized Jarvis-type gc model is suitable to predict P. cathayana transpiration and explains more than 80% of the variation observed in gc, and the relative error was less than 25%, which shows a preferable simulation effect. The root mean square error (RMSEs) between the predicted and measured Ec were 1.91 × 10−3 (with the time lag) and 3.12 × 10−3 cm h−1 (without the time lag). More importantly, Ec simulation precision that incorporates time lag is improved by 6% compared to the results without the time lag, with the mean relative error (MRE) of only 8.32% and the mean absolute error (MAE) of 1.48 × 10−3 cm h−1.

Agricultural drainage is one of the leading contributors to agricultural non-point source (AGNPS) pollution in China. It is difficult to treat due to its dispersed nature. In recent years, although agricultural drain age water has been reused in agricultural production, its poor quality has limited its potential utilization. To optimize its reuse, we designed and tested a treatment system for agricultural-drained water compromising a vegetation buffer, slopes (plant filter), a water collection area, and a soil-retention wall in Hengxi town, Nanjing, Jiangsu Province, China. By exploiting the soil-vegetation buffer strips, nitrogen and phosphorus in the paddy field’s surface drainage are expected to be reduced dramatically. Test results suggest that after applying basal fertilizer, the removal rates of total nitrogen by the soil-vegetation buffer strips are 90.6% and 95.2% for controlled and conventional irrigation-drainage treatments, respectively. In addition, the removal rates of dissolved nitrogen are 92% and 90.7% (controlled and conventional), the removal rates of total phosphorus are 94.2% and 92.9%, and for dissolved phosphorus, the rates are 94.4% and 95%, respectively. These data indicate that drainage water from a paddy field that has been treated through the constructed system could reach the standard of National Class II with two irrigation-drainage methods, while for control treatments water quality can only reach Class V, which is severely contaminated. With this system, the reuse of agricultural water resources could be achieved, which will undoubtedly provide a great potential for agricultural water management in southern China, as well as achieving excellent overall ecological benefits.

We review over twenty years of publications on Soil and Water Assessment Tool (SWAT) applications in arid/semi-arid irrigated agricultural watersheds. Our review reveals strict dominance of the model's use for better understanding water quantity aspects of water management. While this is to be expected given the reality of water scarcity and associated challenges for agricultural production systems in arid/semi-arid regions, the capabilities of SWAT to model water quality have been underutilized. The main modeling challenges are lack of observational data, poor data quality, concerns about simulation accuracy, and technical limitations of the model despite numerous advancements in the last two decades. To deal with these challenges, modelers (i) combined data from different sources with those in existing SWAT databases, (ii) used supplemental tools to estimate missing data and evaluate model performance, (iii) traded off simulation accuracy when the major aim of the study was not undermined, and (iv) developed modular codes, tools, and algorithms to expand the model’s capabilities and improve process representations. A realistic simulation of regional hydrologic fluxes and agricultural water management practices that affect them is essential for meaningful SWAT applications in irrigated dry regions. Modelers are encouraged to apply multi-component calibration (e.g., streamflow, evapotranspiration, crop yield, and groundwater recharge) and report limitations and regional relevance of parameter values to contextualize model performance. We anticipate that model advancements such as conjunctive use of surface water and groundwater, explicit simulation of different irrigation systems, dynamic land use, and impacts of soil and water salinity on crop growth would significantly enhance the utility of SWAT in arid/semi-arid irrigated areas.

The karst rocky desertification is one of the major bottlenecks for the eco-environmental safety and economical sustainable development in karst areas of China. The formation of rocky desertification is influenced by many factors, and the lithology of carbonate rocks has the most profound influence on it as internal factors. The lithological difference of carbonate rocks determines its weathering process and the way of the accumulation and loss of surface soil, which makes the origin, temporal and spatial evolution rule and governance difficulty of rocky desertification different. In this paper, the limestone and dolomite in the moderate and severe rocky desertification region in the Guizhou plateau are selected as the research objects. Stress-dissolution experiments of carbonate rocks are carried out by the simulating open system of the water environment of epikarst zone. The differences in deformation and dissolution characteristics of limestone and dolomite under different stress conditions are analyzed. In addition, the characteristics of surface and internal pore structure of the rocks are analyzed from the microscopic view. The results further explain why the degree of rocky desertification in the dolomite area is lighter than the limestone area, but it is more difficult to control than the limestone area. These results provide a theoretical reference for the controlling of rocky desertification.

The increasing conflicts for water resources appeal for chronological insight into the imbalance water scarcity between upstream and downstream regions. While the changes of water scarcity in whole basins have been widely analysed, the divergent development of water scarcity between upstream and downstream regions received little concern. Here non-anthropologically intervened runoff (natural runoff) was first reconstructed in China's 67 basins for the period 1961–2010 using the Fu–Budyko framework and then systematically evaluated in comparison with the observed data. Divergent changes in water scarcity, including water stress and water shortage, between upstream and downstream regions were analyzed for the period of 1980s–2000s. The results showed that surface water withdrawal rapidly increased from 140.8 billion m3 (9 % of natural runoff) in 1980s to 189.7 billion m3 (14 %) in 2000s, with 73 % increase occurring in North China (North of the Yangtze River). This led to severe water scarcity of approximately 0.4 billion people (29 % of population) in 2000s in comparison with only ~ 0.2 billion people (17 %) in the 1980s, with all increase of water scarcity-threaten population in North China. Since 1990s, the increase of upstream water withdrawal came along with the decrease of downstream surface water availability in most northern basins, leading to slower increase in upstream water scarcity and faster increase in downstream water scarcity. Even though restrict water management policy restrained upstream surface water withdrawal in some northern basins over latest decade, the effect of such a reduction in upstream surface water withdrawal was too little to stop the continued decline in downstream surface water accessibility. Meanwhile, semi-arid/humid basins are following in the footsteps of arid basins by rapidly increasing upstream surface water withdrawal. The Chinese case study provides an all-round observation of the imbalance upstream–downstream development in water scarcity, as well as the experiences and lessons from different water management strategies.

The impacts of graywater irrigation on soil properties and vegetable yields were assessed through a three-year field experiment for Bell Pepper, Chile, and Tomato in El Paso, Texas in the United States. Two irrigation treatments including freshwater (well water and sand filter effluent) and graywater (laundry water) with three replications were utilized in the study. Duncan’s multiple range test at the significance level of 0.05 was used to test changes in soil properties including soil pH, salinity, and sodicity, and mean differences in vegetable growth and yields in terms of fruit height, fruit count, weight, and fruit sizes under freshwater and graywater irrigation treatments. The statistical analysis suggests that no evident salt accumulations or changes in salinity and sodicity were observed at the soil surface in the depth of 0-15cm, while soil pH is increased significantly with graywater irrigation. The growth and yield of Bell pepper and Chile under graywater irrigation tend to increase as compared to freshwater irrigation although the results for the third year were not significant. No yield decreases regarding fruit weight, fruit counts and fruit sizes were observed for all vegetables. It can be concluded from the experimental research that the graywater has shown promising potential as an alternative water supply for vegetable production in the El Paso region, Texas.