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Recent research reveals that extreme climate events arise from the complex interplay of multiple physical drivers across different spatial and temporal scales. Although traditional climate risk and impact assessments consider individual extreme events, it is the synergy of such events that can trigger cascading impacts, exceeding the adaptive capacity of the underlying systems, and resulting in major climate and societal impacts. Compound climate events are defined as the combination of multiple drivers and/or hazards that contribute to societal or environmental risk. This work will address the field of extreme climate and weather events through the assessment of the co-occurrence of droughts and heatwave (CDHW) events. Large-scale circulation drivers, such as atmospheric blocking influence the occurrence and the perseverance of CDHW events. The scope of this study is to evaluate the current state of climate over the Mediterranean in terms of droughts and heatwaves, focusing on their compound impacts, and identifying their large-scale atmospheric circulation drivers. The identification of the CDHW climatology is carried out through the improvement of a novel index tailored to the Mediterranean region. According to the peak-over-threshold approach, CDHW events occur when two or more contributing climate indicators simultaneously exceed a relative threshold. Multiple indicator combinations are examined, and an optimum compound index is developed that successfully quantifies the interrelations of droughts and heatwaves. Extensive statistical analysis is carried out to evaluate their frequency, duration, intensity, and trends during the historical climate period. The analysis is based on reanalysis products and following a data-driven methodology, the role of large-scale atmospheric circulation drivers on the onset, duration, and intensity of the CDHW events is examined using the synoptic climatology approach. The analysis provides the hot-spot regions of CDHW high-impact phenomena over the Mediterranean region and their association with the large-scale atmospheric circulation.
Philippopoulos et al. (Sat,) studied this question.