Modeling the potential of management options to reduce irrigation demand in Western Switzerland

European Agriculture is experiencing the consequences of summer droughts and heatwaves in form of quality and quantity losses for numerous crops and feed production. Water availability for irrigation in the vital summer and fall months is decreasing and therefore, irrigation will most likely not be able to sufficiently mitigate the effects of droughts and heat in the future. Thus, approaches that reduce the need for irrigation are required. We investigate potential water-use reduction strategies based on a modelling framework applied to a selected case study in Western Switzerland, the Broye catchment. The region is characterized by intensive agricultural use and drought-related irrigation bans in summer. In the first step of our project, we quantify the total irrigation demand under current and future climate conditions using the soil-water-atmosphere-plant model SWAP. SWAP mainly simulates water and solute flow in soil as well as vegetation growth by solving a set of equations such as the Richards equations. Irrigation demand is quantified by applying this 1D model to the full range of climatic, soil and land use conditions prevailing in the selected catchment. The model calculates both the irrigation requirements and the yield of various irrigation-intensive crops currently grown in the region, such as potatoes, maize, or sugar beet. In a second step, we use the model to assess the efficiency of different management options to reduce the water demand, such as mulching, organic amendments, biochar application, different tillage methods or the cultivation of better-adapted crops. In future work, we will couple the field-scale model to a catchment-scale rainfall-runoff model to assess the impact of a large-scale application of such measures on the water balance of the catchment.