Title: Extreme precipitation events in the Mediterranean: Spatiotemporal characteristics and connection to large‐scale atmospheric flow patterns
Authors: Nikolaos Mastrantonas, Pedro Herrera‐Lormendez, Linus Magnusson, Florian Pappenberger, Jörg Matschullat
Journal: International Journal of Climatology
Extreme Precipitation Events (EPEs) are associated with devastating consequences for our societies, economies, and environment. Locations in the Mediterranean are also affected by such events. In fact, their magnitude, frequency, and associated damages have increased over the latest years, with even more worrying future projections, as the Mediterranean is considered a “hot spot” of climate change. Thus, it is very important to better understand such natural hazards and their drivers, so we can mitigate their impacts and increase the resilience of our societies.
In our study, we analysed EPE characteristics over the Mediterranean region in space and time, and quantified their relationship to large-scale weather variability, covering the entire Mediterranean.
Initially, we investigated when (in which season) EPEs occurred in the different locations across the study domain. We found a clear divide, with winter being the dominant season for the eastern Mediterranean, and autumn dominating the western parts. We quantified the degree of persistence, meaning how possible it is to have an EPE just a few days after a previous EPE in the same area. The results show that such connections are very strong. For example, 1 in every 5 EPEs occurs within one week from the previous EPE in the same area – for most locations in the Mediterranean. Finally, we discovered some strong connections in simultaneous EPE occurrence at distant areas. For example, in central western Italy, 3 in every 10 EPEs happen simultaneously with EPEs over Montenegro and Croatia, a result of the Apennine Mountain influence.
We additionally quantified connections between localized EPEs and large-scale atmospheric patterns. Using statistical tools, we grouped the daily weather conditions over the Mediterranean into 9 classes of distinct atmospheric characteristics. The analysis showed that each group is preferentially associated with the occurrence of EPEs at different subdomains of the Mediterranean. For coastal areas and highlands in particular, the probability of observing an EPE increases over 4 times under the preferential groups.
Why are these results important? Because the currently used numerical weather prediction models have a hard time predicting localized EPEs for more than a few days in advance. These models can provide useful information however, about large-scale weather variability up to 2–3 weeks ahead. Thus, the identified strong association of EPEs to large-scale patterns, together with their high relationships in space and time, can help us in making better predictions at longer lead-times.