A Simple Approach to Represent Irrigation Water Withdrawals in Earth System Models

The increasing demand for water, driven by population growth and agricultural expansion, underscores the need for accurate representation of irrigation in Earth System Models (ESMs). While a few current-generation ESMs incorporate irrigation, their representation of water withdrawals remains overly simplistic. These models typically source water solely from rivers and, in some cases, the ocean. This oversimplification can lead to inaccuracies in projecting water resources under climate change scenarios. This study presents a simple approach to integrate irrigation water withdrawals within the ISBA-CTRIP global hydrological system, which is the land surface model integrated into the French National Center for Meteorological Research's ESM. The methodology encompasses the withdrawal of water from both groundwater and conceptual small dams. A global data set is employed to impose irrigation water demands on cropland areas. Irrigation water is distributed according to the three main irrigation techniques: flood, sprinkler, and drip. This approach ensures the closure of the global water budget that is essential in climate simulations. The model was evaluated against satellite and in situ observations over the period 1971–2010, demonstrating some improvements in simulating the continental water cycle. Our findings underscore the necessity of incorporating comprehensive irrigation processes in ESMs to account for the intricate interconnections between irrigation practices, water resources, and climate. By enhancing the representation of anthropogenic water withdrawals in ESMs, this study aims at contributing to the development of more robust climate projections which could help building more informed water management strategies in the future.