Rainfall extremes and hydroclimatic trends in Caraguatatuba (SE Brazil) based on CHIRPS and ETCCDI indices (1981–2024)

Abstract Coastal cities are increasingly exposed to complex hydroclimatic pressures shaped by changes in both the intensity and the temporal structure of rainfall. This study examines long-term precipitation variability in Caraguatatuba, southeastern Brazil, using daily CHIRPS data (1981–2024) and ETCCDI indices. Results indicate a significant increase in consecutive dry days (CDD), rising from 29 days in 1981 to 39 days in 2017 ( p = 0.0064), reflecting growing drought-related stress. In contrast, the Rx1day index shows a significant decline ( p = 0.0039), with annual maxima decreasing from 141 mm to 84 mm, and the contribution of very wet days (R95p and R99p) also diminishes ( p = 0.0159 and 0.0271). Spatial analyses reveal strong heterogeneity: urbanized eastern districts exhibit declining extreme-rainfall intensities, whereas forested southwestern sectors continue to experience high-magnitude events modulated by orographic forcing. These patterns suggest that vulnerability may increase not through intensifying extremes, but through longer dry spells and greater rainfall irregularity, which can reduce soil moisture and infiltration capacity and heighten susceptibility to runoff and slope instability. This evolving hydroclimatic regime poses emerging challenges for water management and disaster preparedness in rapidly developing coastal environments.