The role of irrigation on potato yields in Northern Germany under climate change

The agricultural sector is particularly vulnerable to changing weather and climate conditions. Climate projections for Germany until the end of this century demonstrate higher temperatures and a substantial net water deficit during the summer months when agriculture is in high demand for water. Additionally, the frequency and length of dry periods increase as a consequence of climate change. Irrigation was introduced in the 1960s in Northeast Lower Saxony (Germany) to become more resilient to changing weather and climate conditions and prevent yield losses. The region involves today the largest irrigated area in Germany. However, during the drought in 2018 water extractions for irrigation by far exceeded the institutional limit. Water using conflicts are likely to strengthen in the future as the irrigation demand will increase. In this study, we explore the importance of irrigation as a climate change adaptation measure in the region. First, we employ a statistical regression model to investigate whether regional climate, hydrological, and irrigation data on a monthly and county level scale are adequate to describe potato yield changes between 1978 and 2018. Soil moisture information originates from the mesoscale hydrologic model (mHM). Irrigation is estimated based on the climatic water balance and crop water demand. These estimations are scaled with irrigation data from local authorities to account for realistic monthly water withdrawals. Second, we use the process-based crop model EPIC to estimate potato crop yields and to validate the performance of the statistical approach. We analyze future yield changes based on climate model projections for the 21st century using the two approaches. We investigate different irrigation scenarios as a potential climate change adaptation measure. By comparing the statistical and process-based approaches we explore whether a rather simplistic statistical approach captures the main processes of the climate change impact on yields.