Irrigation supports agricultural production, but widespread use of irrigation can perturb the regional and global water cycle. The one‐way coupled irrigation scheme used in some land surface models and Earth system models assumes that surface water demand is always met and ignores the surface water constraints, leading to overestimation of surface water usage, underestimation of groundwater pumping, and unrealistic simulation of their seasonal variability. To better represent the irrigation processes, a two‐way coupled irrigation scheme is developed within the Energy Exascale Earth System Model (E3SM). The new irrigation scheme simulates irrigation water demand and applies irrigation water in E3SM Land Model (ELM), which is coupled to a river routing model and a water management model (MOSART‐WM) that simulate streamflow, reservoir operations, and irrigation water supply. With two‐way coupling, surface water irrigation is constrained by the available runoff, streamflow, and reservoir storage. Simulations were performed for 1979–2008 at 0.5° spatial resolution to estimate irrigation surface water and groundwater use and their seasonality in global and large river basin scales. Compared to one‐way coupling, the two‐way coupling scheme (1) estimates less surface water withdrawal and less return flow due to the surface water constraint; (2) better represents groundwater recharge and groundwater level decline at global scale; and (3) is able to capture the seasonal dynamics of irrigation water allocations which reflect the local water conditions. The new development is an important step to more realistically account for the interactions between human water use and the terrestrial water cycle in an Earth system model.

中文翻译：

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E3SM中完全耦合的地表，河流和水管理模型对全球灌溉特征和影响的模拟

灌溉支持农业生产，但是灌溉的广泛使用会扰乱区域和全球的水循环。在某些陆地地表模型和地球系统模型中使用的单向耦合灌溉方案假定始终满足地表水需求，并且忽略了地表水约束，从而导致高估了地表水使用量，低估了地下水泵送以及对其进行不切实际的模拟季节变化。为了更好地表示灌溉过程，在能源亿亿地球系统模型（E3SM）中开发了双向耦合灌溉方案。新的灌溉方案模拟了灌溉用水需求，并在E3SM土地模型（ELM）中应用了灌溉水，该模型与河流路径模型和水管理模型（MOSART-WM）耦合，后者模拟了径流，水库运营，和灌溉用水。通过双向耦合，地表水灌溉受到可利用的径流，水流和水库存储的限制。在1979-2008年以0.5°空间分辨率进行了模拟，以估算全球和大型流域尺度上的灌溉地表水和地下水的使用及其季节性。与单向耦合相比，双向耦合方案（1）估计由于地表水的限制而减少了地表水的抽取，并减少了回流。（2）更能代表全球范围内的地下水补给和地下水位下降；（3）能够反映反映当地水情的灌溉水分配的季节动态。