Diurnal asymmetry and structural regime shifts in Mediterranean urban temperature records

Abstract

Mediterranean cities are experiencing rapid warming, yet the temporal evolution of their thermal regimes remains insufficiently understood. This study analyzes quality-controlled daily temperature observations (1990–2020) from twelve Mediterranean coastal cities to investigate regional and local dimensions of urban temperature change through monotonic trend analysis, diurnal asymmetry diagnostics, and structural break detection. Results reveal a coherent warming signal, with statistically significant maximum temperature increases in 11 of 12 cities. Conversely, minimum temperature trends exhibit spatial heterogeneity, remaining significant in only four cities. Diurnal asymmetry analysis suggests a non-significant tendency toward daytime-dominant warming across the study cities, although this basin-wide asymmetry does not reach statistical significance. Structural break analysis identifies significant regime shifts in nighttime temperatures in four cities between 2000 and 2010. These findings suggest that observed warming patterns may reflect a combination of regional climate forcing and possible localized influences, although attribution of these influences is beyond the scope of this study. The results highlight the need for integrated planning strategies to mitigate both daytime heat intensification and nighttime heat retention in rapidly warming Mediterranean environments.