Quantifying the response of water and carbon balances to land cover and climate extremes across Germany

Abstract. Land cover and extreme weather events are closely connected to water yield and carbon sequestration. Understanding the tradeoffs between carbon and water and how they respond to human disturbances is critical for quantifying ecosystem services. The monthly scale ecosystem model, WaSSI, was tested and applied across Germany for mapping carbon and water balances from 2001–2019. We estimated that Germany generates 84.86 billion m3 of discharge and sequesters 106.03 Tg of carbon annually. The eastern states were comparatively drier than the rest of the country, as most of their precipitation was lost as evapotranspiration. Croplands, urban areas and Evergreen Needle Forests (ENF) provide 82.5 % of the water yield, while the forests sequester the major share of carbon (56.3 %) altogether. The results highlight the importance of sparse land covers (e.g. wetlands) in carbon sequestration. Findings also suggest that national water yield and carbon balances are sensitive to extreme events. In 2002 and 2013, due to high precipitation, the stocks of key ecosystem services were notably higher. Similarly, during the drought years of 2003 and 2018, the services were reduced drastically, but we found that buffers from the previous year played an important role in mitigating negative impacts. This study highlights that, when integrated with local data, a relatively simple modelling approach is adequate to answer questions of coupled water and carbon responses to climatic variability at a large scale. We conclude that land management of both forests and croplands are vital to sustain ecosystem services under a changing climate.