Stable isotope trends in precipitation and extreme climate indicators: insights from Berlin and the Lusatian Lignite Mining District, Germany

Abstract Northeastern Germany, including the Lusatian Lignite Mining District and Berlin, has experienced dry and hot springs and summers in recent years, with adverse consequences for water resources, ecosystems and society. Here, we quantified long-term changes in (i) extreme climate and meteorological drought indicators (1948–2022) and (ii) the stable isotopic composition (δ 18 O, δ 2 H, ) of precipitation (1978–2022). Our results show an increased frequency of temperature driven extreme events ((very) hot days, warm nights) and of dry days (> 6.5% in Berlin 1991–2020 versus 1961–1990). Concurrently, the number of frost and snow days decreased, especially in recent years. The frequency of severe and extreme meteorological droughts, represented by the climatic water balance deficit (SPEI), has increased. Between 2018 and 2022, Berlin experienced the longest period of precipitation and climatic water balance deficit since 1948. The observed climatic changes coincide with a significant positive trend in the 45-year record of stable isotopes of precipitation, which is statistically significant ( p > 0.05) annually and during summer. In spring, only δ 18 O values show a significant positive trend, leading to a significant negative trend for the d-excess. We show that the positive trend in isotope patterns is strongly correlated ( r > 0.5) with temperature during winter and moderately (0.3 < r < 0.5) during spring and summer indicating that climate warming is now detectable in the isotope record. For the Lusatian mining region, the results suggest that climate change needs greater consideration in regional water management, and a localized stable water isotope record of precipitation would be beneficial.