Abstract
Century-scale drought variability remains poorly understood globally due to sparse instrumental records and limited paleoclimate reconstructions. Yet, quantifying long-term forced and natural drought variability is key for assessing the extremeness of today’s events. Here, we use 20 ensemble members from a 600-year climate simulation (ModE-Sim, 1420-2009) and modern reanalysis data (ERA5-Land, 1950-2024) to place recent drought extremes in a multi-century context. Drought magnitude and timing are measured using the annual maximum potential cumulative water deficit (PCWD), which integrates atmospheric moisture demand and supply, the timing of precipitation, snow melt, and radiation. We analyze trends, low-frequency variability, and externally forced changes across regions globally. Results show that hydroclimate variability differs widely across regions and can match the magnitude of forced events. In the modern era (2000-2024), record PCWD exceeds the record in the multi-century and multi-ensemble reference (1420-1969) in 13 of 43 regions. Although modern droughts are not unprecedented in the remaining 30 regions over the past 600 years, the statistics of drought events have shifted substantially. Moderate (5-year) drought extremes have at least doubled in frequency in 20 regions, while the severity of rare (30-year) extremes exceeds the magnitude of a 30-year extreme estimated from the 20 ensemble and 600-year context in 36 regions. The number of regions exhibiting record-high annual PCWD varies strongly with the chosen reference period. Our findings reveal a fundamental transformation in drought regimes where modern droughts are generally more intense and frequent than those of the preindustrial past across much of the global land surface.
