Intensification of Heat Extremes and Spatial Variability of Rainfall in Mainland Portugal (1980–2025): Insights from ETCCDI Indices Based on ERA5-Land Data

This study analyzes trends in 18 temperature- and precipitation-related indices recommended by the Expert Team on Climate Change Detection and Indices (ETCCDI) across mainland Portugal over the most recent 46-year complete period (1980–2025), using ERA5-Land reanalysis data. Prior to the computation of the indices, daily ERA5-Land extreme temperature and precipitation data were validated against ground-based observations, showing good agreement and confirming the suitability of the reanalysis dataset for assessing climate extremes at the national scale. The results reveal a consistent and statistically significant warming signal across the study area, with the strongest increases observed in southern and inland regions. The frequency of extreme heat events has intensified markedly since the early 2000s. In contrast, precipitation-related indices display high spatial variability and trends with limited statistical significance, reflecting both genuine climatic heterogeneity and the inherent challenges of reproducing rainfall extremes in complex terrain using reanalysis data. The combined interpretation highlights an emerging climatic asymmetry—robust and spatially coherent warming versus localized and uncertain precipitation trends—underscoring distinct regional vulnerabilities. The findings provide actionable insights for climate services, supporting the design of region-specific adaptation strategies in Portugal, especially the need to address increasing heat stress in southern regions and the growing exposure to short-duration heavy rainfall in northern areas.