Evapotranspiration and Feedback Effects with Climate and Land Use Change in the Eastern German Lowlands

Evapotranspiration (ET) is a vital component of the hydrological cycle, mediating energy, water, and carbon exchanges on land surfaces and the atmosphere, which are critical for agricultural water availability. Understanding the spatiotemporal variability of ET and its relationship with atmospheric drivers and land use/land cover change (LUCC)  is crucial for assessing environmental impacts on regional water cycles and improving water resource management.

This study focuses on the lowlands in eastern Germany. It is a predominantly agricultural region with a continental climate. Despite being one of the driest areas in Germany, 45% of its land is used for agriculture. Using environmental data obtained by MODIS (ET, temperature, solar radiation, and LUCC) and the German Weather Service (relative humidity, precipitation, wind speed, soil moisture, and vapor pressure deficit), ET trends and drivers are analyzed from 2000 to 2020. The objectives are to (i) identify key factors influencing ET and (ii) estimate the effects of climate change and LUCC on ET. 

Results reveal a slight increase in annual ET (taking into account the European vegetation period), with spatial trends showing increases of up to 7.17%, particularly in the southern and southeastern regions. Over the same period, Temp and VPD rose by 37% in the western and eastern areas, while RH decreased by more than 55% in areas experiencing higher Temp and VPD levels. Significant LUCC was observed, including a 22.24% decrease in cropland-to-grassland conversion and a 14.75% increase in grassland-to-cropland conversion, leading to a 21% decline and a 10% increase in ET, respectively.

Among climatic factors, VPD, Temp, RH, and SR had the most substantial influence on ET variability, contributing 28.24%, 27.68%, and 26.84%, respectively. Overall, climate change accounted for 97% of ET variation, underscoring its dominant role. Notably, discrepancies between ET and climatic drivers in western, eastern, and southeastern regions align with drought periods documented in this study. Our findings highlight the important role of Temp and RH in agricultural and water resources management, particularly in the context of climate change.