Understanding drought conditions and impacts on key ecosystem services in a low-mountain watershed in Germany

Europe has experienced increasing frequency of climate extremes which caused negative impacts on the ecosystems and various socioeconomic sectors. In this research, we examined the drought conditions and impacts in Weisse Elster, a low-mountain watershed, in Central Germany. First, we studied the temperature and precipitation trends in the watershed. We found that seasonal and annual temperatures had an increasing trend. Precipitation had a decreasing trend during summer and an increasing trend in the winter and annual scales. By using drought indices, namely standardised precipitation-evapotranspiration index (SPEI) and standardised precipitation index (SPI), we found that drought conditions have been worsening. We used the Water Supply Stress Index (WaSSI), an integrated ecosystem services model developed by U.S. Forest Services, to simulate two key ecosystem services: surface water flow and carbon sequestration. The model showed satisfactory performance when evaluated against discharge, evapotranspiration and gross primary productivity (GPP) observations. To understand the drought vulnerability of different areas and ecosystems, we compared water yield (WY), net ecosystem productivity (NEP), and soil moisture (SM), averaged for the five most intense drought events, to the averages of the total study period (57 years). We found that droughts caused a significant reduction in WY (54%), NEP (18%), and SM (13%) in the region, with some areas being more affected than others. Urban landcover saw a 41% reduction in water flow, while agriculture and grasslands landcovers experienced significant reductions in generated water flow (63% and 60%, respectively). Deciduous forests had a 53% reduction in water flow and coniferous forests experienced a loss of around 37%. All landcover types saw a similar impact on carbon sequestration during droughts. Coniferous forests sequestered 21% less carbon while deciduous forests, grasslands, and agriculture landcover sequestered 18%, 17%, and 17% less carbon, respectively. We emphasise that there is an urgent need to improve climate resilience in the region and to reduce drought risks in different sectors to adapt to climate change.