Drought impact on productivity: Data informed process-based field-scale modeling of a pre-Alpine grassland region

Abstract. Grasslands are the basis for milk and meat production in alpine and pre-alpine regions, where climate warming is occurring twice as fast as in global average. Warmer and drier conditions have been found to lead to versatile effects on grassland productivity and yields depending on pedo-climatic conditions. Experimentally, it has been discovered that higher and cooler elevations benefit from warming in the absence of drought, whereas lower elevations are more vulnerable to yield losses under climate change. These findings are based on sites covering only a few discrete climatic, soil, and management conditions. This limitation is overcome in the present study, where we compiled a highly detailed field-scale dataset including cutting dates (2018–2020) from remote sensing, informing regional grassland management routines of the biogeochemical model LandscapeDNDC which was applied in the pre-Alpine Ammer region (530 m a.s.l to 2200 m a.s.l., 4600 km²) in southern Germany. The strongest predictor of yields was the management intensity with an average yield increase of 1.2 t ha^-1 a^-1 per additional cut and associated manure application. At the regional scale for 3- and 5-cut fields, yields decrease on average with increasing elevation by up to 0.4 t ha^-1 a^-1 per 100 m. We found a mean regional yield decrease of 4 % in the drought year 2018 compared to the year 2020 with average climatic conditions. In addition, due to support of mineralization, soil organic carbon had a positive effect on yields, especially in drier years. Yield increases of 0.09 to 0.22 t ha^-1 a^-1 per % increase in soil organic carbon were observed. Our results illustrate the complex interactions between management, soil, and climate factors influencing grassland yields, including differences in their importance in drought and non-drought years.