Heatwaves in central Mediterranean trends and categories

Abstract

Heatwaves are a familiar feature to the Mediterranean summer; however, with climate change they are expected to increase in occurrence as well as magnitude. Heatwaves occurrence in the Central Mediterranean between 1973-2018 is investigated using temperature data from seven stations (Brindisi, Sigonella, Cozzo Spadaro, Trapani, Cagliari, Malta, and Carthage) in the region. Due to various definitions being utilised in heatwave studies, this study uses two definitions for heatwaves detection, the absolute and relative approaches. In order to identify heatwaves, hot days were defined as days exceeding the climate monthly normal (base-period 1961-1999) by at least 5oC or exceeding the 95th percentile calculated from base-period 1981-2010. A total of 1311 and 1545 hot days were identified. Both methods detected a significant number of heatwave events, 334 and 388 respectively. Both show a significant, positive trend in heatwave occurrence throughout the 45 years. This study also analyses the severity of heatwaves using the Heatwave Severity Index, which calculates the cumulative sum of difference from heatwave daily temperature from the climate normal. The results of this index were used to categorize heatwaves according to severity from mild to high.