Increasing Floods and Intensifying Droughts: The Future of Hydrological Extremes in a Warming Climate

Understanding how climate change alters the frequency and severity of hydrological extremes is critical for anticipating regional vulnerabilities and guiding adaptation. In this study, we analyze changes in the magnitude, intensity, and duration of extreme streamflow events, both floods and droughts, under RCP4.5 and RCP8.5 scenarios using the FutureStreams dataset. This dataset, driven by multiple CMIP5 climate models, enables a global-scale assessment across all Intergovernmental Panel on Climate Change (IPCC) Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Adaptation (SREX) regions. We identified events using percentile-based thresholds derived from historical (1976–2005) streamflow distributions and evaluated future extremes relative to these baselines across seasonal and decadal time slices. Our results show an apparent intensification of extremes, particularly under RCP8.5, with substantial increases in flood and drought events in climate-stressed regions such as South Asia, the Mediterranean, Central Australia, and Northern Europe. The seasonal dynamics of these changes, such as summer drought intensification and winter flood increases, underscore the compound effects of warming, altered precipitation, and snowmelt patterns. While the most significant increases occur in regions with a known history of hydrological stress, some areas with historically moderate variability also exhibit growing extremes, especially toward the end of the century. These findings highlight the urgency of emissions mitigation and region-specific adaptation planning in addressing the increasing risks posed by future hydrological extremes.