Climate change intensifies the temporal persistence of droughts through a shift from seasonal to prolonged drought regimes

Abstract

Climate change is altering not only the frequency and magnitude of droughts, but also their temporal structure. In addition to becoming more severe, droughts may persist longer and increasingly extend across consecutive seasons and years. This study investigates changes in the temporal symmetry of global meteorological droughts, defined here as the tendency for droughts to remain confined within a single season or to persist across consecutive seasons, using monthly precipitation and potential evapotranspiration from bias-corrected simulations from the Coupled Model Intercomparison Project Phase 6 (CMIP6) for the historical period (1985–2014) and future projections (2015–2100) under two emission scenarios (SSP2-4.5 and SSP5-8.5). Drought conditions were quantified using the Standardised Precipitation–Evapotranspiration Index (SPEI), and global drought events were characterised using mean frequency, mean duration, maximum duration, mean severity, and total severity. To evaluate the shift from seasonal droughts toward more persistent drought regimes, the authors examined drought persistence from summer to autumn and analysed the temporal evolution of future droughts. Results indicate declines in SPEI under both future scenarios, with stronger drying under SSP5-8.5. Seasonal drought characteristics intensify most clearly in the warm season and extend into autumn, indicating that droughts are becoming not only more frequent, but also more persistent and severe. The persistence analysis reveals stronger continuity of drought from summer into autumn, while scenario comparison shows that high-emission forcing amplifies these temporal changes. Together, these results suggest a transition from predominantly seasonal drought behaviour toward longer, more persistent, and potentially multi-year drought regimes. These findings highlight the need to explicitly account for drought persistence and cross-season continuity in climate risk assessment, water resources planning, and adaptation policy.