Abstract
Abstract. The Mediterranean (MED) Basin is a climate change hotspot that has seen drying and a pronounced increase in heatwaves over the last century. At the same time, it is experiencing increased heavy precipitation during wintertime cold spells. Understanding and quantifying the risks from compound events over the MED is paramount for present and future disaster risk reduction measures. Here, we apply a novel method to study compound events based on dynamical systems theory and analyse compound temperature and precipitation events over the MED from 1979 to 2018. The dynamical systems analysis quantifies the strength of the coupling between different atmospheric variables over the MED. Further, we consider compound warm–dry anomalies in summer and cold–wet anomalies in winter. Our results show that these warm–dry and cold–wet compound days are associated with large values of the temperature–precipitation coupling parameter of the dynamical systems analysis. This indicates that there is a strong interaction between temperature and precipitation during compound events. In winter, we find no significant trend in the coupling between temperature and precipitation. However in summer, we find a significant upward trend which is likely driven by a stronger coupling during warm and dry days. Thermodynamic processes associated with long-term MED warming can best explain the trend, which intensifies compound warm–dry events.
Highlights
The Mediterranean (MED) Basin is considered a climate change hotspot (Giorgi, 2006) and has seen winter drying as well as a pronounced increase in summer heatwaves over recent decades (e.g. Mariotti, 2010; Hoerling et al, 2012; Shohami et al, 2011; Nykjaer, 2009)
Summer heatwave trends observed over the historical period are mainly driven by thermodynamic changes, such as increasing temperatures, that exacerbate soil drying and daily maximum temperatures
The null hypothesis is that the JJA (DJF) observed percentage agreement is due to chance, and to compute the significance the following steps have been followed: (i) create n = 1000 datasets of random dates, with the same number of elements in each dataset as we have for the compound dynamical extremes (CDEs); (ii) compute the percentage of agreement between CDEs and compound events’ days for each dataset and grid point; (iii) pool together all the random percentage values and compute their 1st and 99th quantiles for each grid point; (iv) check whether the observed percentage values fall outside the random quantile values, and if this is the case, consider the percentage values statistically significant at the 1 % level (p value < 0.01)
Summary
The Mediterranean (MED) Basin is considered a climate change hotspot (Giorgi, 2006) and has seen winter drying as well as a pronounced increase in summer heatwaves over recent decades (e.g. Mariotti, 2010; Hoerling et al, 2012; Shohami et al, 2011; Nykjaer, 2009). De Luca et al.: Compound events over the Mediterranean conditions by the end of the 21st century (Zappa et al, 2015; Mariotti et al, 2015; Scoccimarro et al, 2016; Hochman et al, 2018; Samuels et al, 2018; Seager et al, 2014; Barcikowska et al, 2020; Goubanova and Li, 2007; Giorgi and Lionello, 2008; Giannakopoulos et al, 2009; Beniston et al, 2007) Such climatic changes imply more severe and frequent summer heatwaves and droughts (Fischer and Schär, 2010; Giorgi and Lionello, 2008; Beniston et al, 2007; Giannakopoulos et al, 2009) and an increase in heavy precipitation events notwithstanding the decline in total precipitation (Scoccimarro et al, 2016; Samuels et al, 2018; Goubanova and Li, 2007; Giannakopoulos et al, 2009; Tramblay and Somot, 2018).
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