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Understanding the agro-hydrological processes and water productivity of canal- and well-irrigated systems is vital for agricultural water management in arid regions. In this study, the Agro-Hydrological & chemical and Crop systems simulator (AHC) was used in a distributed manner to evaluate the agro-hydrological processes and to assess water productivity under the conditions of canal- and well-irrigated systems. With the Heji irrigation system (Heji) located in the arid upper Yellow River basin, Northwest China as the case study area, the AHC was calibrated and validated by the field observation data of 2018 and 2019. Then the model was used in a distributed manner for the entire Heji. Results showed that there were significant differences in the agro-hydrological processes and water productivity between canal- and well-irrigated areas. The spatially averaged actual evapotranspiration was larger in canal-irrigated areas, and the cumulative net bottom water and salt fluxes were mainly downward in well-irrigated areas. The applied water was used more efficiently with higher equivalent water productivity of water applied (EWP IP) in canal-irrigated areas. However, the total water consumption (evapotranspiration) was in higher efficient utilization with higher equivalent water productivity of water consumption (EWP ET) in well-irrigated areas. These findings can provide implications for regional irrigation water management and salinity control in the arid areas. • A GIS-based 1D model was used in canal- and well-irrigated systems. • Water balance in canal-irrigated areas is different from that in well-irrigated areas. • The risk of salt accumulation is more serious in canal-irrigated areas. • Canal- and well-irrigated areas shows differences in water productivity. [ABSTRACT FROM AUTHOR]

• Coupling AHC and SHAW models simulates year-round agro-hydrological processes in cold arid areas. • Coupled model performance was evaluated with two-year field experiments. • The impacts of various irrigation and groundwater management strategies were assessed. • Appropriate irrigation and groundwater management strategies for farmland were suggested. Quantitatively assessing the impact of irrigation and groundwater management strategies is crucial for improving water productivity and soil salinity control in cold arid areas with shallow groundwater tables (CAASGT). However, existing studies often focus on specific periods, either the crop growth period or the freeze–thaw period, due to the lack of appropriate models that can accurately represent both soil freeze–thaw and crop growth processes. This limited focus results in incomplete year-round insights, given the significant differences and interactions in hydrological processes during these two periods. In this study, we coupled the agro-hydrological model (i.e., the AHC model) and the cold region hydrological model (i.e., the SHAW model) to simulate the year-round agro-hydrological processes and crop growth in CAASGT. The coupled model was rigorously calibrated and validated using two years of field experiment data collected from a maize field in the upper Yellow River basin (YRB). Subsequently, the validated model was employed to analyze the effect of different irrigation and groundwater management scenarios on crop yield, soil salinity, and water productivity in two hydrological years (dry and wet years). Results indicated that increasing groundwater depth was beneficial for soil salinity control in all scenarios but reduced maize yield at low irrigation levels. Autumn irrigation proves essential for soil salinity control, with reducing the irrigation amount in autumn irrigation period having a more significant impact on maize yield than that in growing season. Additionally, soil thawing time significantly affects soil salt accumulation and crop yield, with earlier thawing time leading to more severe salt accumulation at the end of the freeze–thaw period, restraining maize seedling growth and decreasing maize yield. These results are expected to offer year-round insights into improving water productivity and soil salinity control in CAASGT. [ABSTRACT FROM AUTHOR]

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

Water scarcity and salt stress are two main limitations for agricultural production. Groundwater evapotranspiration (ET g ) with upward salt movement plays an important role in crop water use and water productivity in arid regions, and it can compensate the impact of deficit irrigation on crop production. Thus, comprehensive impacts of shallow groundwater and deficit irrigation on crop water use results in an improvement of irrigation water productivity (IWP). However, it is difficult to quantify the effects of groundwater and deficit irrigation on IWP. In this study, we built an IWP evaluation model coupled with a water and salt balance model and a crop yield estimation model. As a valuable tool of IWP simulation, the calibrated model was used to investigate the coupling response of sunflower IWP to irrigation water depths (IWDs), groundwater table depth (GTDs) and groundwater salinities (GSs). A total of 210 scenarios were run in which five irrigation water depths (IWDs) and seven groundwater table depths (GTDs) and six groundwater salinities (GSs) were used. Results indicate that increasing GS clearly increases the negative effect on a crop's actual evapotranspiration (ET a ) as salt accumulation in root zone. When GS is low (0.5–1 g/L), increasing GTD produces more positive effect than negative effect. In regard to relatively high GS (2–5 g/L), the negative effect of shallow-saline groundwater reaches a maximum at 2 m GTD. Additionally, the salt concentration in the root zone maximizes its value at 2.0 m GTD. In most cases, increasing GTD and GS reduces the benefits of irrigation water and IWP. The IWP increases with decreasing irrigation water. Overall, in arid regions, capillary rise of shallow groundwater can compensate for the lack of irrigation water and improve IWP. By improving irrigation schedules and taking advantages of shallow saline groundwater, we can obtain higher IWP. [ABSTRACT FROM AUTHOR]

Unreasonable irrigation water saving and salinity control practices (IWS-SCPs) have resulted in a shallow groundwater table, severe soil salinization and low water use efficiency in the upper Yellow River basin (YRB), Northwest China. In our study, a framework was developed by coupling the agro-hydrological model, i.e., AHC (Agro-Hydrological & chemical and Crop systems simulator) with a decision-making method, i.e., VIKOR (VlseKriterijuska Optimizacija I Komoromisno Resenje), and then a comprehensive evaluation index was calculated to assess the IWS-SCPs for maize and sunflower in the upper YRB. The AHC model was calibrated and validated with two years of field measured data, and then it was used to perform the simulations of agro-hydrological processes corresponding to the designed scenarios considering the irrigation depth and groundwater table depth (GWD) under the conditions of different hydrological years and degrees of soil salinization. The simulated crop yield, soil salinity variation, and crop water productivity were used as the evaluation indicators to search for appropriate IWS-SCPs of the target crops. The results showed that the recommended IWS-SCPs for maize were those with GWDs between 2.1 − 2.3 m and irrigation depths approximately 10% lower for non-saline soils in wet years and 10% higher than the present irrigation for slightly and moderately saline soils in normal and dry years. Whereas, the IWS-SCPs with GWD between 1.5 − 2.2 m and an irrigation depth of approximately 10 − 30% lower than the present situation could be recommended for sunflower in wet years and normal years regardless of saline soils and in dry years of non-saline soils. The developed framework and the obtained results are expected to provide a decision tool and implications for improving irrigation efficiency and salinity control in the arid upper YRB as well as other areas with similar climate conditions and shallow groundwater. • Coupling AHC model and VIKOR method provided a decision tool for water saving and salinity control. • The framework could be used as a decision tool for irrigation management and salinity control. • The appropriate groundwater depth for maize is 0.6 m deeper than that for sunflower. • Approximately 10%− 30% of irrigation water can be saved for sunflower in the upper Yellow River basin. [ABSTRACT FROM AUTHOR]

[Display omitted] • A process simulation-based framework was developed for RFE trade-off. • Farmland water–carbon–nitrogen processes and ecosystem service values were quantified. • The negative ESV of local practices accounts for approximately 10% of the positive ESV. • The optimal FINS for spring wheat farmland was obtained by using the framework. • Approximately 53 % irrigation water and 32 % N fertilizer can be saved for wheat in the upper Yellow River Basin. Improving food production and resource utilization efficiency and mitigating the functional degradation of agroecosystems are major challenges worldwide. However, few studies have reconciled the conflicts among resources, food, and ecology (RFE) in agricultural production. This study develops a water–carbon–nitrogen process simulation-based framework for RFE trade-off by coupling the agro-hydrological model, i.e., AHC (Agro-Hydrological & chemical and Crop systems simulator) with the ecosystem service value (ESV) assessment method and decision-making method, i.e., VIKOR (VlseKriterijuska Optimizacija I Komoromisno Resenje). The framework is capable of (1) quantifying farmland ESVs; (2) reconciling conflicts among resource utilization, food production and ecosystem development by optimizing farmland irrigation and nitrogen (N) application strategies (FINS). The framework was used to analyze the FINS, and then to obtain the compromise decision focusing on a lower negative ESV and the maximizing group utility decision focusing on a higher yield and positive ESV for spring wheat farmland in Northwest China. Results indicated that under the local FINS, i.e., 450 mm irrigation and 340 kg ha−1 N application, the total ESV generated by spring wheat farmland per season was [4.76, 4.87] × 104 CNY ha−1. Among these ESVs, every 1 CNY ha−1 positive ESV generation was accompanied by approximately 0.11 CNY ha−1 negative ESV. Compared with the local FINS, the compromise decision, i.e., the FINS with 210 mm irrigation and 200 kg ha−1N application, significantly reduced negative ESV but caused slight losses in yield and positive ESV, while the maximizing group utility decision, i.e., the FINS with 210 mm irrigation and 260 kg ha−1N application, increased yield and positive ESV but resulted in a small negative ESV mitigation. Moreover, both FINSs could save irrigation water and N fertilizer resources, and improve water and N productivity to various degrees. This framework has excellent performance in reconciling conflicts among RFE systems and generating coordinated solutions and has potential to achieve sustainable development goals in agricultural RFE systems. [ABSTRACT FROM AUTHOR]

Numerical simulation is an efficient approach for investigating the salt and water movement through soil profile and predicting of crop response to soil water deficit and salinity. In this study a coupled model that describes the soil water and solute transport by means of HYDRUS-1D model and crop growth process by means of growth module of EPIC was used. The model was calibrated and validated against field data, collected during two growing seasons in field plots of winter wheat irrigated with four levels of irrigation amount and water salinity of 5 ds m −1 at the Fengqiu State Key Agro-Ecological Experimental Station, in North China Plain. The model was also used to evaluate the salinity stress on evapotranspiration (ET), grain yield and water use efficiency (WUE) and long-term use of saline water on grain yield and salt accumulation. Visual inspection and the obtained statistical parameters values showed that good agreement between measured and simulated data of soil water content, salt concentration, ET and grain yield. Evapotranspiration values of winter wheat were reduced under salinity stress conditions, mainly by reducing crop transpiration. The grain yields were reduced due to salinity stress, but the change trend of WUE was associated with precipitation amount. Increasing per saline water irrigation amount is an effective way to reduce the WUE decline rate under the low rainfall growing season as like that in simulation year. The average of ten years grain yield confirmed that a yield potential exceeding 86% could be maintained by saline water with 5 ds m −1 when per irrigation volume more than 0.8 E, E denotes evaporation from an uncovered, 20 cm diameter pan positioned 0–5 cm above the crop canopy. There has a slight salt build-up after ten years simulation, and the quantity of salt accumulation decreased with the increase of irrigation volume. Thus, more attention should be paid to the sustainability of irrigated agriculture with low irrigation volume when using saline water irrigation. On the whole, field observations combined with the coupled model could be used to evaluate different agricultural managements on grain yield and soil salinity. [ABSTRACT FROM AUTHOR]

Water scarcity has been a crucial issue for sustainable irrigated agriculture in the arid regions. In these regions where conserving water is paramount, optimal allocation and utilization of irrigation water is particularly important. In this study, a process-based regional economic optimization (PBREOP) model was developed for maximizing irrigation water use efficiency and economic benefit of an irrigation system. The PBREOP model is a two-level optimization model with combined use of an agro-hydrological model (SWAP-EPIC). The first level (farm scale) dealt with the optimal distribution of irrigation water and cropping pattern considering various crops and soils in a subsystem, using a non-linear programing technique. The second level (district scale) sought out the optimal strategy for irrigation water allocation among different subsystems using a dynamic programing algorithm. The crop water production functions (CWPFs) were an important component of the first-level objective function. They were derived with the SWAP-EPIC model considering different irrigation alternatives. The model was solved using the decomposition-harmonization method for large systems. The Yingke Irrigation District (YID) in the middle Heihe River basin, Northwest China was used as a case to test the PBREOP model. Nine CWPFs for three major crops and three major soils were firstly derived based on the simulations of different irrigation levels and climate conditions (20 years). Next, the PBREOP model for YID was established with 11 subsystems, and applied to the irrigation water use optimization under five water supply scenarios. Results showed that the total economic benefit in YID could be increased by 15% on average through the optimization of water allocation and cropping pattern with the same water supply amount as that of the current situation. A variation range of the risk was also obtained with considering the impacts of climate uncertainties. Scenario analysis showed that the total irrigation water could be reduced by 23% on average without benefit reduction when compared to the benefit of the present situation. Model test indicated that the proposed PBREOP model can efficiently optimize irrigation water use and cropping pattern on a regional scale. [ABSTRACT FROM AUTHOR]

Summary Water saving in irrigation is a key issue in the upper Yellow River basin. Excessive irrigation leads to water waste, water table rising and increased salinity. Land fragmentation associated with a large dispersion of crops adds to the agro-hydrological complexity of the irrigation system. The model HYDRUS-1D, coupled with the FAO-56 dual crop coefficient approach (dualKc), was applied to simulate the water and salt movement processes. Field experiments were conducted for maize, sunflower and watermelon crops in the command area of a typical irrigation canal system in Hetao Irrigation District during 2012 and 2013. The model was calibrated and validated in three crop fields using two-year experimental data. Simulations of soil moisture, salinity concentration and crop yield fitted well with the observations. The irrigation water use was then evaluated and results showed that large amounts of irrigation water percolated due to over-irrigation but their reuse through capillary rise was also quite large. That reuse was facilitated by the dispersion of crops throughout largely fragmented field, thus with fields reusing water percolated from nearby areas due to the rapid lateral migration of groundwater. Beneficial water use could be improved when taking this aspect into account, which was not considered in previous researches. The non-beneficial evaporation and salt accumulation into the root zone were found to significantly increase during non-growth periods due to the shallow water tables. It could be concluded that when applying water saving measures, close attention should be paid to cropping pattern distribution and groundwater control in association with irrigation scheduling and technique improvement. [ABSTRACT FROM AUTHOR]

Irrigation is essential for agriculture in the middle Heihe River basin, Northwest China, due to water scarcity and dryness of climate. The diverted river water for agriculture is being gradually reduced which requires an increased water use performance to meet crop water requirements and to maintain crop yields. It is therefore crucial to better know about the present agro-hydrological processes, irrigation performance and water productivity, and to further investigate the potential water saving on a regional scale. In this study, a distributed agro-hydrological model was developed by close coupling of an agro-hydrological model (SWAP-EPIC) and ArcInfo geographic information system. Combined effects of weather, crop, soil and irrigation factors were considered. The Yingke Irrigation District (YID), in the middle Heihe River basin, was chosen as case study, where experiments were conducted at both field and regional scales in 2012–2013. Parameters relative to soils and crops were first calibrated with field observed data and the model was later used in a distributed manner to simulate the agro-hydrological process of YID. Results showed that water productivity was spatially varied and quite small due to excessive irrigation water use. Crop evapotranspiration averaged 589 mm and deep percolation was 125 mm on average, which accounted for 21% of total irrigation. Analysis of the target scenario simulation indicated that the improvement of water conveyance and irrigation scheduling could lead to a 30% reduction of deep percolation, and save 15% of irrigation water without negative effects on crop yields. [ABSTRACT FROM AUTHOR]

Irrigation is a prerequisite for the sustainable development of agricultural production. With the existing of water resources shortage and climate change, it is of great importance to explore the variation of crop irrigation water requirement (IWR) in the Yellow River Basin (YRB). Based on 1974–2017 meteorological dataset from 96 stations, we analyzed the spatio-temporal variation characteristics of meteorological factors and crop IWR during the growing seasons of four main crops including spring wheat, winter wheat, spring maize and summer maize, respectively. Furthermore, we explored the dominant meteorological factors of the crop IWR variation. The results indicated that daily mean temperature (T) had a significant upward trend, while the effective precipitation (P eff) did not change significantly during the growing season of each crop in the past 44 years. Crop IWR had increasing trend with 9.9 mm/decade, 4.3 mm/decade, 6.4 mm/decade for spring wheat, winter wheat, spring maize respectively, while a slight decreasing trend with − 1.7 mm/decade for summer maize. It is noted that extremely significant increase in crop IWR were mostly located in Ningxia, southern Gansu and eastern Qinghai. Moreover, P eff , net radiation (R n) and relative humidity (RH) were identified as the dominant meteorological factors influencing variations of IWR for all crops. In the context of significant increase in T and uncertain future precipitation patterns, IWR for spring wheat, winter wheat and spring maize in the YRB has shown an upward trend which is not favorable to the sustainable development of water resources. It is urgent to take effective water-saving measures to hedge the adverse impact of climate change on agriculture. These findings can provide scientific basis for rational allocation of agricultural water resources in the YRB. • Irrigation water requirements of main crops in the Yellow River Basin were quantitatively evaluated. • The spatio-temporal variation of meteorological factors during the crop growing seasons was investigated. • The spatial distribution and changing trend of crop irrigation water requirements were characterized. • The dominant meteorological factors of crop irrigation water requirements variation were found out. • It is urgent to take effective water-saving measures to hedge the adverse impact of climate change on agriculture. [ABSTRACT FROM AUTHOR]

[Display omitted] • An integrated simulation-optimization framework is proposed for irrigation planning. • It makes dynamic decision of irrigation planning possible. • It achieves the maximum credibility level of the fuzzy objective function. • It controls salt accumulation at the end of crop growth period through constraints. An integrated simulation-optimization framework is developed under uncertainty to enhance irrigation water productivity and control salinity in an arid area. A full fuzzy dependent linear fractional programming approach is formulated by incorporating fuzzy dependent-chance programming, fuzzy credibility-constrained programming and linear fractional programming within a general framework of irrigation planning. Then, simulation module concerning water, salt balance process and crop water-salt production functions enables to quantify daily physical process of water and salt movement among the soil water, crop root zone and groundwater aquifers. Thus, this study can readily handle fuzzy uncertainty existing concurrently in the ratio objective (i.e., economic water productivity) through the concept of fuzzy dependent chance and double-sided constraints. It can also simultaneously provide the maximum credibility level that the objective is achievable and credibility levels implying that optimal solutions are believable. Besides, daily variations of simulated physical parameters are illustrated corresponding to management strategies. To demonstrate its applicability, it's then applied to a case study of irrigation planning in the Jiefangzha Irrigation Subarea in Hetao Irrigation District, northwest China. Results can clearly analyze tradeoffs among satisfaction degree of fuzzy objective, fuzzy constraints and optimal solutions. Moreover, by examining different management targets and salt accumulation constraints, this study demonstrates the merits and importance of the work to promote irrigation water productivity and control salinity. Dynamic decision making of irrigation planning is possibly made by coupling daily simulation and optimization modules. Therefore, these findings can support decision makers to identify appropriate solutions for irrigation planning. [ABSTRACT FROM AUTHOR]

• A simulation-based regional irrigation water optimization model (SRIOP) is developed. • The model tightly links an agro-hydrological model with a regional optimization. • A three-level optimization framework is formulated for model coupling and solution. • The impacts of climate condition changes and resulting uncertainty are considered. • Process-based optimal spatial allocation of irrigation water use can be obtained. It is attractive and advantageous to realize process-based optimization of irrigation water use on large scales. In this study, a simulation-based regional irrigation water optimization model (SRIOP) was developed for watershed-scale optimal spatial allocation based on dynamic responses of agro-hydrological process and its spatial differences. The SRIOP model tightly linked a field-scale agro-hydrological model (SWAP-EPIC) with an optimization algorithm (NSGA-II) in a regional multi-level optimization framework. It performed at three levels that sequentially dealt with optimal irrigation water allocation on field, irrigation district and irrigated watershed scales, with two objectives of maximizing yield/benefit and minimizing irrigation water. The model was tested with a case study in the major irrigation system (MIS) of middle reaches of the Heihe River basin, northwest China. The optimal spatial distribution of irrigation water showed a decreased variation coefficient (0.17) and increased irrigation benefit (9.8% higher) as compared with that of the present year, and better reflected the effects of multi-level collaboration and crop-soil field distribution. The impacts of climate condition changes on optimized results and resulting uncertainty were also quantified and evaluated through optimizations in different climate years. The case study indicated that the model is a computationally efficient and feasible approach for process-based optimization on large scales with considering impacts of climate condition changes. [ABSTRACT FROM AUTHOR]

Shallow groundwater often presents multiple behaviors in supporting the sustainability of arid agroecosystems. The behaviors are especially important and complicated for the arid irrigated areas with fragmented land-use types. In the view of understanding the role of shallow groundwater in such areas, the MODFLOW and MT3DMS (with the assistance of HYDRUS-1D) were used to simulate groundwater flow and salt transport in a typical observation site of the arid upper Yellow River basin (YRB). The original MODFLOW was modified with introducing a variable expression of specific yield, aiming to improve the modeling accuracy in shallow groundwater environments. The model was calibrated and validated using the observation data of groundwater depth and drainage in 2013 and 2012, respectively. Groundwater evapotranspiration and lateral water-salt exchange among different land-use types were simulated and analyzed; meanwhile, the dry drainage effect of non-cultivated natural land was quantitatively interpreted. Results indicated that the fragmented land-use/planting pattern (with different irrigation scheduling) resulted in significant lateral groundwater flow and water/salt redistribution among different land-use fields during irrigation. The groundwater evapotranspiration ranged at about 160–220 mm for different land-use types, reaching to 0.30–0.45 of plant evapotranspiration (ET pt) during the growing seasons. This effectively supplemented the plant water use in arid climate, especially for the unirrigated cultivated land (during some stages) and the non-irrigated natural land. Meanwhile, the lateral groundwater flow drove salt migrating from the cultivated land to the natural land. The natural land accumulated 27–40% of salts introduced by irrigation, playing a significant role in accommodating salts (i.e. the dry drainage effect). Moreover, our modeling work further implied that the reliable groundwater modeling in arid and shallow groundwater areas required a more detailed model conceptualization and more accurate information of land-use distribution, irrigation scheduling, and local microrelief than the general understanding in the past. • A detailed local-scale groundwater model was established for a typical observation site. • Multiple roles of shallow groundwater system with fragmented land use was elucidated. • Groundwater evapotranspiration and lateral water-salt exchange dynamics were analyzed. • Dry drainage effect of non-cultivated natural lands was quantitatively interpreted. • Implication for improving accuracy of the previous modeling work was proposed. [ABSTRACT FROM AUTHOR]

Scenario analysis is the basis of developing rational water management practices (WMPs) for watersheds. How to predict future hydrological responses on a regional-scale is still a challenge for modeling work in irrigated watersheds with shallow groundwater environments. Therefore, this paper presents an efficient realization of predicting regional agroecosystem responses and searching for appropriate WMPs, through using a water balance-based, semi-distributed hydrological model (SWAT-AG). The scenario case study is carried out in the Jiyuan Irrigation System located in the Hetao of upper Yellow River basin, based on the calibrated and validated modeling work in our previous companion paper. Eight scenarios of water-saving practices (WSPs) are proposed, with consideration for reducing irrigation depth and controlling initial groundwater depth. Then the coupled responses of agroecosystem processes to various WSPs are predicted for the case study region in 2012 and 2013, mainly related to the groundwater depth, root zone soil water and salinity, and crop yield/natural vegetation biomass. Based on the analysis for proposed scenarios, the 100% of present irrigation depth combined with increasing initial GWD by 50 cm are recommended as appropriate WSPs for dry years, and the 80% of present irrigation depth combined with increasing initial GWD by 100 cm are recommended for wet years, in order to maintain good environmental conditions for both crops and natural vegetation. In addition, results show that SWAT-AG could overcome the scale/function limitations of traditional soil/crop models and also avoid computational issues of numerical models. We further point out that the scenarios in reality will be more complicated and comprehensive in time and space, and thus the predictions should be updated accordingly. Overall, this case study fully presents the feasibility and practicality of using the SWAT-AG model to realize the scenario response analysis and water management decision-making on a region scale for irrigated watersheds with shallow groundwater environments. • Regional realization of predicting agroecosystem responses was carried out. • Scenario study predicted the coupled responses to water-saving practices. • Appropriate water-saving management was suggested for maintaining agroecosystems. • Approach showed high potential in supporting water use in arid irrigated areas. [ABSTRACT FROM AUTHOR]

• Equivalent water productivity (WP) was proposed and proved to be useful in WP assessment. • WP is scale dependent due to water reuse through shallow groundwater systems. • Natural vegetation should not be ignored when considering water productivity of a whole region. • Water reuse reduces WP compared with direct use in salt affected areas. • Efficient irrigation systems are needed for WP improvement in salt affected areas. Water productivity (WP) expressed as the yield produced per unit volume of water is an important indicator of water use in arid and semi-arid areas. Due to complex plant cover and hydrological processes, the quantification and assessment of WP are usually difficult to determine, especially at the regional scale. In this study, an arid irrigated agro-ecosystem in the upper Yellow River basin was selected as a case study area. Based on field observation and model simulation results, the WP of irrigation water (WP I), water applied (WP (I + P)) and evapotranspiration (WP ET) were calculated. Equivalent water productivity (EWP) of irrigation water (EWP I), water applied (EWP (I + P)) and evapotranspiration (EWP ET) were proposed and calculated to unify the disparate WP for various crops and natural vegetation. Results showed WP I and WP (I + P) decreased with the increase of water application for all plants except watermelon, indicating supplemental irrigation to watermelon is urgent to improve its production and WP (I + P). The spatially averaged WP ET (kg m−3) was 2.47 for maize, 0.80 for sunflower, 12.3 for watermelon, 1.39 for wheat and 0.65 for natural vegetation. WP ET for natural vegetation was usually lower in this salt stressed area compared with other water stressed areas. The EWP revealed the rank order of WP for different crops and natural vegetation: watermelon > wheat > maize > sunflower for EWP I ; natural vegetation > wheat > watermelon > maize > sunflower for EWP (I + P) ; and wheat > sunflower > watermelon > maize > natural vegetation for EWP ET. The relationship between EWP (I + P) and EWP ET was scale dependent due to the water reuse phenomena among different land cover types and the canals through the shallow groundwater system. Ignoring natural vegetation will result in considerable bias in the estimation of the regional scale water productivity (16 % in this study). WP improvement strategies such as transferring irrigation water from less productive (sunflower) areas to productive (vegetable and natural vegetation) areas, reducing bare soil evaporation and constructing a timely and accurate irrigation-drainage system were provided. [ABSTRACT FROM AUTHOR]

• J s was modified considering sapwood width and insertion direction. • Groundwater table rise due to canal infiltration increased J s by 5.5–25.8% • Impact of ET o and groundwater on J s was quantified. • The threshold of groundwater table depth to support J s is about 3.6 m. Shelterbelts play an important ecological function in arid irrigation land, while competing for water which otherwise supports crop growth. Estimation of shelterbelt water consumption from groundwater is essential to better manage shelterbelts in irrigation districts, but often a challenging task due to its geometry and varying accessibility to groundwater. In the study, sap flow of Populus popularis planted along an irrigation canal was measured during two growing seasons (2016–2017) to investigate its response to varying shallow groundwater. Considering the radial pattern of sap flux density (J s) and measurement azimuthal effect, corrected J s was adopted to better represent transpiration. The results indicate that increased soil moisture and groundwater table during irrigation periods with water flowing in the canal enhance relative J s of shelterbelt by 5.5–25.8% from the non-irrigation intervals. The threshold of groundwater depth (3.6 m) is identified, beyond which transpiration of the seven-year-old shelterbelt becomes very low. Greenbelt transpiration strongly depends on groundwater within the threshold, and can be estimated through an exponential function of the ratio of atmospheric demand and groundwater depth. Besides, with the decrease of reference evapotranspiration from June to September, the sensitivity of shelterbelt transpiration response to groundwater table depth was increased. This study provides necessary information to evaluate farmland shelterbelt transpiration for rational water resource allocation to meet the ecological water requirement in arid areas with shallow groundwater. [ABSTRACT FROM AUTHOR]