In arid and semiarid areas, the issues of water security, ecological security, and food security are tightly interlinked. Understanding the water‐ecosystem‐agriculture (WEA) nexus in such areas is critical to their sustainable development. This study presents a basin‐scale integrated ecohydrological model and a paradigm for analyzing the WEA nexus through physically based modeling. The integrated model is successfully applied to the Heihe River Basin (HRB), the second largest endorheic river basin in China. A system analysis of the WEA nexus in the HRB is performed using the validated model. The major findings are as follows. First, reducing the amount of irrigation water applied to the midstream of the HRB produces widely varying effects on the water balance of the basin. Second, a threshold of 11.5 × 10⁸ m³/yr is found for the streamflow from the midstream region to the downstream region, beyond which the contribution of the streamflow to the recovery of vegetation is trivial in the short term. Third, the trade‐off among water conservation, ecosystem protection, and food production in the HRB is strong, and it is highly sensitive to the water management strategy employed. Evaporative water‐saving practices are more desirable than direct water‐saving regulation of irrigation water from the perspective of the WEA nexus. Overall, the results of the study provide insights into the allocation of water resources, ecosystem conservation, and agricultural development in the vast arid and semiarid areas of the world.

In many flood-prone areas, it is essential for emergency responders to use advanced computer models to assess flood risk and develop informed flood evacuation plans. However, previous studies have had a limited understanding of how evacuation performance is affected by the arrangement of evacuation shelters (with respect to their number and geographical distribution) and human behaviors (with respect to the heterogeneity of household evacuation preparation times and route-searching strategies). In this study, we develop an integrated socio-hydrological modeling framework that couples (1) a hydrodynamic model for flood simulation, (2) an agent-based model for evacuation management policies and human behaviors, and (3) a transportation model for simulating household evacuation processes in a road network. We apply the model to the Xiong'an New Area and examine household evacuation outcomes for various shelter location plans and human behavior scenarios. The results show that household evacuation processes are significantly affected by the number and geographical distribution of evacuation shelters. Surprisingly, we find that establishing more shelters may not improve evacuation results if the shelters are not strategically located. We also find that low heterogeneity in evacuation preparation times can result in heavy traffic congestion and long evacuation clearance times. If each household selects their own shortest route without considering the effects of other evacuees' route choices, traffic congestion will likely occur, thereby reducing system-level evacuation performance. These results demonstrate the unique functionality of our model with respect to supporting flood risk assessment and advancing our understanding of how multiple management and behavioral factors jointly affect evacuation performance.

It is imperative to understand the interconnectedness of water use and hydrological impacts for water policy design underlying varying hydrological conditions across space and over time. However, such analysis remains difficult, constrained by the lack of appropriate modeling tools that fully integrate water policies, water use, and hydrological processes with high spatiotemporal resolutions. To address this challenge, this study proposes a distributed policy design scheme featuring spatially variable and temporally dynamic policies for conjunctive surface water‐groundwater management in large river basins. A fully integrated modeling framework is developed to tightly couple (a) an agent‐based model for farmers' water use under distributed water policies and (b) a physically based hydrological model for surface water‐groundwater processes. The modeling framework is applied to the Heihe River Basin to assess water use and hydrological impacts under distributed water policies. By using the distributed policy scheme to adjust a water policy (e.g., groundwater tax) across space and over time, we found that hydrological outcomes can be improved without adversely reducing agricultural water supply. For example, by shifting the implementation of a high groundwater tax from dry to wet years, a rise of the water table by 0.28 m (0.03–0.95 m across different irrigation districts) can be achieved while the total water supply is maintained at a similar level. Furthermore, hydrological externality effects among nearby districts can be explicitly identified and quantified based on assessments of spatially varying water policies. This study highlights the need for water policy design to consider spatiotemporal variations in the physical hydrological system.