Impacts of climate and land-surface change on catchment evapotranspiration and runoff from 1951–2020 in Saxony, Germany
Abstract. This paper addresses the question how catchment scale water and energy balance have responded to climatic and land-surface changes over the last 70 years in the federal state of Saxony, in eastern Germany. Therefore observational data of hydrological and meteorological monitoring sites from 1951–2020 across 71 catchments are examined in a relative water and energy partitioning framework to put the recent drought induced changes in a historical perspective. A comprehensive visualization method is used to analyze the observed time series. The study focuses on changes in decadal time scale and finds the largest decline in observed runoff in the last decade (2011–20). The observed decline can be explained by the significant increase in aridity, caused by the reduction of annual mean rainfall and an increase in potential evaporation at the same time. In a few mainly forested head water catchments the observed decline in runoff was even stronger than predicted by climate conditions alone. These catchments are still on the recovery from past widespread forest damages in the 1970–80s resulting in a continuous increase of actual evapotranspiration due to forest regrowth. In contrary runoff stayed almost constant in other catchments despite an increase in aridity. These catchments showed declines in actual evapotranspiration which could be signatures of either contributing groundwater at longer time scales or drought induced vegetation damages.
These results highlight that water budgets in Saxony are in an unstable, non-stationary regime due to significant climatic changes and regional impacts of land-surface changes such as forest health. The recent decreases in the mean annual runoff are substantial and must be taken into account by the authorities for fresh water management.
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