Impacts of Increased Agricultural Irrigation on Regional Groundwater Recharge

Climate change, with its rising temperatures and altered precipitation patterns, is expected to reduce soil moisture during critical phases of plant growth. This will lead to increased water stress and lower crop yields. As the frequency of low-yield years rises, farmers will become increasingly interested in irrigation as a means to stabilize crop production. This trend could accelerate if government subsidies for irrigation infrastructure increase in response to recurring low yields.

This shift towards increased irrigation may be particularly relevant for Germany, where in most regions irrigation is limited to few specialty crops. The present study focuses on the potential impact of increased irrigation in a 400 km² area south of Stuttgart, encompassing the morphological catchment of the Ammer River and part of the Neckar Valley near Tübingen. Since irrigation is not widely practiced in this region, it provides a unique opportunity to clearly demonstrate the effects of a possible transition to irrigation agriculture.

To analyze these impacts, the crop model ExpertN was used to simulate irrigation requirements for each of the region's 300 soil-weather units. The model incorporates detailed processes, such as water flow within soil layers (Richards equation) and evapotranspiration (based on the Penman-Monteith equation), to accurately describe soil moisture dynamics. Additionally, the model includes nitrogen cycling, enabling an assessment of increased irrigation to nitrate leaching.

The study highlights key outcomes, including the water demand for irrigation, additional moisture losses through evaporation, and increases in deep percolation under varying irrigation intensities. Furthermore, we evaluate the effects of irrigation on regional crop production, providing valuable insights for sustainable agricultural management under a changing climate.