Extremely hot summers preceded by spring droughts in the Mediterranean

18:00 Tuesday 28 May




Ana Russo (Portugal) 1; Célia Gouveia (Portugal) 2; Emanuel Dutra (Portugal) 1; Pedro M.M. Soares (Portugal) 1; Ricardo M. Trigo (Portugal) 1

1 - Instituto Dom Luiz; 2 - IPMA

The Mediterranean is often affected by extreme weather events [1], such as droughts and heatwaves, often impinging negative impacts on different economic and social activities [1].

Several studies stressed the role played by recent climate change in the increased likelihood of occurrence of some of these extremes [1,2], with emphasis on the fact that temperature extremes are expected to occur more frequently under increasing Greenhouse Gases concentrations [3].

Several studies have put into evidence the existence of positive feedback mechanisms between droughts and heatwaves, particularly in semiarid environments [4,5]. We propose to analyze to what extent the occurrence of summer extremely hot days and nights in the Mediterranean is preceded by the occurrence of drought events in the spring and early summer.

The characterization of droughts was performed using the Standardized Precipitation Evaporation Index (SPEI) and the Standardized Precipitation Index (SPI) for the 3-, 6- and 9-months timescales, as obtained from CRU TS4.01 database for the period 1980-2014 (0.5ox0.5o). 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 (v14).

Results show that the most frequent hottest month for the Mediterranean region occurs either in July or August. Most regions exhibit statistically significant negative correlations, i.e. positive NHD/NHN following negative SPEI/SPI values and vice-versa. Particularly for Iberia, the highest negative correlations are often observed for the smallest timescales (3_or 6_months), whereas for the Balkans conclusions are not so clear. The occurrence of these lagged influences between dry winter and spring months, followed by summer heatwaves represents a potential for NHD/NHN early warning.

This analysis allowed to identify the Iberian Peninsula, northern Italy, northern Africa, and the Balkans as the main hotspots of predictability of extremely hot temperatures in the summer preceded by the occurrence of drought events in the spring or early summer.


[1] Hovø 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

Acknowledgments: This work was partially supported by Fundação para a Ciência e a Tecnologia (Portugal) by the project IMPECAF (FCT, PTDC/CTA-CLI/28902/2017) and UID/GEO/50019/2013 – Instituto Dom Luiz. A.Russo thank FCT for the grant SFRH/BPD/99757/2014.