Regional Aspects of Observed Temperature and Precipitation Trends in the Western Mediterranean: Insights From a Timescale Decomposition Analysis

Abstract

The observed warming in the Western Mediterranean (WMed) region over recent decades is projected to continue, outpacing the global average, making the region a prominent climate change hotspot. Even within this relatively small area, the combination of natural climate variability and anthropogenic climate change creates significant spatial variation in extreme climate events. This study analyzes mean seasonal temperature and precipitation trends in the WMed using ECMWF Reanalysis v5 (ERA5) data from 1951 to 2020 taking into consideration the climatic heterogeneity of the region. A non-hierarchical K-Means clustering method was applied to delineate nine climatically homogeneous regions within the WMed. A timescale decomposition analysis was then conducted to disentangle long-term, decadal, and interannual variability components of seasonal data. Results indicate that long-term trends explain most of the total observed variance in temperature (∼65%), whereas interannual natural variability dominates observed precipitation (∼60%). These patterns vary seasonally, with the strongest warming trends along the Mediterranean coast of the Iberian Peninsula and northern Africa in summer and the most significant drying trends in the southwestern Mediterranean during both summer and winter. The influence of different modes of climate variability in the observed trends is assessed and appears to contribute to winter drying, but no evidence was found of its influence on warming trends. This study lays a foundation for future climate change detection and attribution efforts in the WMed, emphasizing the need for sub-regional analysis due to the region's pronounced heterogeneity.