Are modern droughts unprecedented?

作者：Patricia Helpap, Stefan Brönniman, Ralf Hand, Jörg Franke, Benjamin D. Stocker · 年份：2026 · DOI：10.5194/egusphere-egu26-2598 · 研究领域：Tree-ring climate responses、Hydrology and Drought Analysis、Climate variability and models

Drought variability over the last millennium remains poorly understood in a global context--reflecting the sparsity of instrumental records and reconstructions from paleoclimatic proxies. Yet, a quantification of the long-term forced and unforced variability of droughts across regions globally is key for assessing the extremeness of currently observed drought events. Here, we use 20 ensemble members from a 600-year ensemble simulation (ModE-Sim, 1420 - 2009) and modern reanalysis data (ERA5-Land, 1950-2024) to place recent drought extremes in a multi-century historical context. For measuring drought magnitude and timing, we consider the annual maximum potential cumulative water deficit (PCWD)--a physically and ecologically-grounded metric, integrating atmospheric moisture demand and supply and the relative timing of daily precipitation, snow melt, and radiation. To investigate changes over the simulated period, we assess trends, low-frequency variability, and effects of external forcing. Our results show that internal hydroclimate variability differs across regions and can be of the same magnitude as forced events. Towards the modern era (2000-2024), PCWD exceeds the reference (1420-1969) with unprecedentedly high values in 13 out of 43 regions. Despite modern droughts not being unprecedented in most regions when considering a 600 year reference and unforced variability across 20 ensemble members, our results show that the statistics of droughts are widely shifting. Moderate ...