Beyond Annual Averages: Multi‐Scale Rainfall Variability, Drought Indicators, and Seasonal Shifts Under a Changing Climate

ABSTRACT Understanding rainfall variability across multiple temporal scales, especially for regions with strong seasonality, is essential for anticipating hydrological risks under climate change. This study investigates how precipitation patterns in the Florida Peninsula may evolve under two CMIP6 climate scenarios (SSP2‐4.5 and SSP3‐7.0) across two future periods: a near‐term window (2026–2055) and a mid‐ to late‐century horizon (2056–2085) critical for long‐range water resources planning. Simulations from 18 General Circulation Models (GCMs), bias‐corrected against the North American Land Data Assimilation System (NLDAS), were analysed to assess annual totals, monthly climatology, drought indicators, and rainy‐season onset and demise. Results show that while mean annual rainfall may remain stable or even increase in some regions, precipitation becomes more variable at monthly and seasonal scales. Increased coefficients of variation, more frequent exceedance of cumulative rainfall deficit thresholds, and more erratic rainy‐season onsets indicate heightened drought risks despite little change in annual totals. Regional contrasts are pronounced, with northern Florida tending toward wetter futures with modest variability increases, whereas southern Florida shows stronger drying tendencies, greater variability, and higher vulnerability to seasonal deficits, especially under SSP3‐7.0. These findings underscore the importance of adaptive, climate‐informed, and region‐specific strategies for water management that move beyond annual averages to account for short‐term variability and persistent deficits across multiple scales. The methodological contribution is a decision‐oriented, seasonality‐aware diagnostic workflow showing that shortage‐relevant deficit frequency and wet‐season timing uncertainty can intensify even when mean annual rainfall changes are small, offering a transferable template for other highly seasonal water‐supply regions.