| ABSTRACT | The Mediterranean is often affected by extreme weather (EW) events [1], such as droughts and heatwaves, which are two of the most frequent EW events in the Mediterranean [1], having negative impacts on different economic and social activities [1].
Several studies have stressed the role played by recent climate change in the increase likelihood of occurrence of some of these extremes [1,2], with emphasis on the fact that temperature extremes are expected to occur more frequently [3].
A number of studies have put into evidence the existence of several positive feedback mechanisms between droughts and heatwaves, particularly in semiarid environments such as the Mediterranean [4,5]. Here, we propose to analyze if the occurrence of summer extremely hot days and nights in the Mediterranean is preceded by the occurrence of drought events in spring and early summer. This is assessed initially by computing the correlation coefficients between the number of hot days and nights in the regions’ hottest months with a drought indicator in the prior months.
The evolution and characterization of drought in the Mediterranean was performed using the Standardized Precipitation Evaporation Index (SPEI) and the Standardized Precipitation Index (SPI) for three different time scales (3-, 6- and 9-months), as obtained from CRU TS4.01 database for the period 1980-2014 with a spatial resolution of 0.5o. The number of hot days and nights per month (respectively NHD and NHN) is determined using the ECAD-EOBS daily dataset for the same period and spatial resolution (dataset v14).
The most frequent hottest months in the Mediterranean are July and August and the magnitude of correlations obtained between detrended NHD/NHN and the preceding 3-months SPEI/SPI are usually higher than those attained for longer timescales. Most regions exhibit significantly negative correlations, i.e. high (low) NHD/NHN following negative (positive) SPEI/SPI values, and thus a potential for NHD/NHN early warning. Finally, spatial patterns of correlation values between the NHD/NHN with SPI and SPEI differ, with SPEI characterized by slightly higher values observed mainly for the 3-months timescale.
References
[1] Hov Ø et al., 2013. ISBN (electronic) 978-82-7144-101-2.
[2] Sillmann J et al., 2013. J Geophys Res, 118, 2473–2493.
[3] Fischer EM and Schär C, 2010. Nature Geoscience, 3, 398.
[4] Seneviratne SI et al., 2010. Earth Sci. Rev. 99, 125–161.
[5] Miralles DG et al., 2014. Nature Geoscience, 7, 345
Acknowledgements
This work was partially supported by Fundação para a Ciência e a Tecnologia (Portugal) by the projects IMDROFLOOD (FCT, WaterJPI/0004/2014) and UID/GEO/50019/2013 - Instituto Dom Luiz. A.Russo thank FCT for the grant SFRH/BPD/99757/2014. |