More Droughts, More Irrigation? Modeling the Adaptive Behavior of German Farmers to Hydrometeorological and Socioeconomic Change 

The shifting precipitation patterns and rising temperatures in Central Europe and Germany present an existential challenge for farmers. Recent severe summer droughts, such as those in 2003 and 2018, underscore the imperative for farmers to adapt to evolving climatic conditions, for instance through the application of irrigation in areas where it was previously unnecessary or economically unfeasible. However, expanding the currently only 3% irrigated agricultural area in Germany has the potential to significantly impact freshwater resources and hydrological processes. Here, we model the adaptive behavior of farmers regarding irrigation, by employing an empirically validated multi-agent system (MAS) model. This model simultaneously simulates decisions about annual crop choices, acreages, and irrigation water application. Spatially disaggregated, the MAS model is calibrated using an Econometric Mathematical Programming (EMP) approach, based on historical land use data for eight major field crops. To account for the implications of future climate change, we couple the MAS model with a statistical crop yield model driven by meteorological indicators and soil moisture anomalies derived from the mesoscale Hydrologic Model (mHM) for a EURO-CORDEX scenario ensemble (RCP2.6, RCP4.5, RCP8.5). Socioeconomic variables that influence farmers' decisions, including changes in crop prices, costs, and subsidies, are projected based on Shared Socioeconomic Pathway (SSP) scenarios. Across various combinations of SSP and RCP scenarios, we find a notable surge in irrigation water demand. This development is particularly pronounced in SSP3-RCP8.5, where the MAS model projects several irrigation hotspots with a high irrigation water demand. Shifts in cropping patterns thereby significantly affect the resulting irrigation water demand. To dissect the effects of hydrometeorological, socioeconomic, and policy changes on irrigation water demand, we conduct sensitivity analyses on individual parameters. The MAS model emerges as a robust tool for analyzing farmers' adaptive behavior and assessing the impact of diverse policies on future irrigation water demand. This research contributes valuable insights into agricultural adaption under changing environmental and socioeconomic conditions.