Exploring the possibilities to reduce irrigation demands through adaptations in soil and crop management

In Central Europe, increasing temperatures and declining summer precipitation intensify the water and heat stress on crops and reduce water availability for irrigation from rivers and groundwater. Thus, approaches that reduce the need for irrigation are required. In this study, we quantify the potential of soil and crop management adaptations to reduce irrigation deficits for a mid-sized rainfed catchment in Switzerland. The Broye catchment, comprising 68 % agricultural land with a notable portion dedicated to irrigated agriculture, faces frequent summer irrigation bans. We employ the field-scale agro-hydrological model (SWAP) aiming to 1) quantify irrigation demand at the catchment scale, 2) assess the impacts of temporary irrigation bans on irrigation deficits, and 3) explore the potential of soil and crop management adaptations to reduce these irrigation deficits. SWAP simulates horizontal solute, heat and water flow in the vadose zone and crop growth at a daily timestep. The model calibration process involves a comprehensive global sensitivity analysis and parameter optimization. The optimization aims to maximize the model's fit to reference data on crop yield and seasonal irrigation amounts from the study region. Spatial climate, land use, and soil input data enable the quantification of irrigation water demand on the catchment scale. We simulated the exceptionally hot and dry summer of 2022, revealing a 57 % deficit in water supply and again emphasizing the importance of reducing reliance on irrigation. We further evaluate the effectiveness of measures such as increased soil organic carbon content and planting earlier maturing crop varieties in reducing irrigation demand. Our findings provide valuable insights for sustainable water management in midsized rainfed catchments, particularly in the face of climate change and evolving water use conflicts. As a next step, we plan to couple the field-scale model with a catchment-scale rainfall-runoff model to evaluate the effects of implementing such measures on the catchment's water balance.