Abstract
An important aspect of inevitable surprises, for the climate system, is the potential of occurrence of compound extreme events. These can be events that occur at the same time over the same geographic location or at multiple locations within a given country or around the world. In this study, we investigate the spatio-temporal variability of summer compound hot and dry (CHD) events at European level and we quantify the relationship between the occurrence of CHDs and the large-scale atmospheric circulation. Here we show that summer 1955 stands out as the year with the largest spatial extent characterized by hot and dry conditions (~21.2% at European level), followed by 2015 (~20.3%), 1959 (~19.4%), and 1950 (~16.9%). By employing an Empirical Orthogonal Function (EOF) analysis we show that there are three preferred centers of action of CHDs over Europe: Fennoscandia, the central part of Europe, and the south-eastern part of Europe. Overall, hot and dry summers are, in general, associated with persistent high-pressure systems over the regions affected by CHDs, which in turn reduces the zonal flow and diverts the storm tracks southward. The high-pressure systems associated with each mode of variability largely suppresses ascending motions, reduces water vapor condensation and precipitation formation, leading to drought conditions below this atmospheric system. This study may help improve our understanding of the spatio-temporal variability of hot and dry summers, at European level, as well as their driving mechanisms.
Highlights
The amplitude of the loadings over the southern part of Europe are much smaller compared to the positive ones over Fennoscandia, we argue that EOF1 is a good indicator for the spatiotemporal variability of compound hot and dry (CHD) over the northern part of Europe
The observed increase in CHDs, which severally impacted the society, economy, and the environment over the past decades, has brought the scientific community to make an extensive analysis of the variability, trends, and future projection of these events, either at global scale (Feng et al, 2020; Ridder et al, 2020; Mukherjee and Mishra, 2021) or at regional scale (Kattsov et al, 2005; Von Buttlar et al, 2018; Hao et al, 2019; Russo et al, 2019; Vogel et al, 2019; Bezak and Mikoš, 2020; Kong et al, 2020)
We explored the spatio-temporal variability of CHDs at European level and we quantified the relationship between the occurrence of CHDs and the large-scale atmospheric circulation
Summary
During the last decades a significant increase in the concurrence of hot summers and severe droughts has been observed (Seneviratne et al, 2012; Zscheischler et al, 2018; Feng et al, 2020; Raymond et al, 2020). An increase in the co-occurrence of hot and dry events over the observational period as well as in future projections has been found (Diffenbaugh et al, 2017; Zscheischler et al, 2018; Manning et al, 2019; Feng et al, 2020). Overall, understanding the interactions between several number of competing events is much more complex than understanding the drivers of individual events
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