A comparative analysis of temperature trends at Modena Geophysical Observatory and Mount Cimone Observatory, Italy

Abstract Global warming has become a critical environmental, social, and economic threat, with increasing frequency and intensity of extreme weather events. This study aims to analyse temperature trends and climate indices in the Po Valley, a significant economic and agricultural region in Italy, by examining data from two historical stations: the urban Modena Observatory and the rural Mount Cimone Observatory. The analysis extends previous studies to 2018, assessing the magnitude of climate changes since the 1950s and isolating the Urban Heat Island (UHI) effect in Modena. Significant warming trends were confirmed at both sites, with in maximum (TX) and minimum (TN) temperatures trends nearly doubling from 1981 to 2018 compared to 1951–2018. For example, TX trends reached 0.84°C·decade −1 in Modena and 0.62°C·decade −1 at Mount Cimone, while TN trends were 0.77 and 0.80°C·decade −1 , respectively. Extreme climate indices showed a substantial increase in warm days and nights (TX90p and TN90p, respectively). Particularly we found TX90p of 27.5 days·decade −1 in Modena and 15 days·decade −1 at Mount Cimone while TN90p of 29.5 days·decade −1 in Modena, 22 days·decade −1 at Mount Cimone. The UHI effect significantly impacts Modena's temperature trends. Urbanization contributes up to 65% of the rise in warm nights. Specifically, frost days decreased by 1.88 days·decade −1 (37% of Urban Contribute, UC), tropical nights increased by 5.16 days·decade −1 (57% UC), warm nights increased by 12.7 days·decade −1 (65% UC), and cool nights decreased by 3.19 days·decade −1 (39% UC). Overall, the study underscores the importance of considering both global and local factors in regional climate trend analysis.