Characterisation of Recent Climate Extremes in Mainland Portugal Using ETCCDI Indices and Validated ERA5-Land Data

To address the need for updated climate analysis in Portugal, spatiotemporal trends in climate extremes from 1980 to 2023 were studied, overcoming the limitations of outdated observational datasets. The high-resolution ERA5-Land reanalysis dataset was used, having first been validated against gap-filled observational records from a Portuguese water resources data system. Eighteen core indices from the Expert Team on Climate Change Detection and Indices (ETCCDI)—nine related to temperature and nine to precipitation—were calculated using daily data for 1,004 grid points. Monotonic trends in the annual indices were identified using the non-parametric Mann–Kendall test, with magnitudes quantified by Sen’s slope estimator. The trend analysis revealed significant and widespread warming. Statistically significant increasing trends were observed for indices related to warm extremes, such as tropical nights (TR) and warm days (TX90p), particularly in southern and interior regions, while a decrease in cold extremes was noted. Precipitation trends were found to be more spatially varied, although a notable increase in consecutive dry days (CDD) is evident across the country, especially in the south, alongside a general decreasing trend in consecutive wet days (CWD). A comprehensive, high-resolution assessment of recent changes in climate extremes across Portugal is thus provided, offering critical evidence to inform targeted regional adaptation strategies, improve water resource management, and support national climate resilience actions. Future research should include climate change scenarios to identify projected changes, using recent historical data—such as that employed in this study—as a robust baseline for comparison.