Abstract
Abstract. In previous studies the Western Mediterranean Oscillation index (WeMOi) at daily resolution has proven to constitute an effective tool for analysing the occurrence of episodes of torrential precipitation over eastern Spain. The western Mediterranean region is a very sensitive area, since climate change can enhance these weather extremes. In the present study we created a catalogue of the extreme torrential episodes (≥200 mm in 24 h) that took place in Catalonia (NE Iberia) during the 1951–2016 study period (66 years). We computed daily WeMOi values and constructed WeMOi calendars. Our principal result reveals the occurrence of 50 episodes (0.8 cases per year), mainly concentrated in the autumn. We confirmed a threshold of WeMOi ≤ −2 to define an extreme negative WeMO phase at daily resolution. Most of the 50 episodes (60 %) in the study area occurred on days presenting an extreme negative WeMOi value. Specifically, the most negative WeMOi values are detected in autumn, from 11 to 20 October, coinciding with the highest frequency of extreme torrential events. On comparing the subperiods, we observed a statistically significant decrease in WeMOi values in all months, particularly in late October and in November and December. No changes in the frequency of these extreme torrential episodes were observed between both subperiods. In contrast, a displacement of the extreme torrential episodes is detected from early to late autumn; this can be related to a statistically significant warming of sea temperature.
Highlights
The Mediterranean seasonal precipitation regime is characterised by rainy winters and dry summers, linked to the westerly atmospheric circulation in winter and to the subtropical anticyclone belt in summer
The highest frequency of torrential events (≥ 100 mm in 24 h) over the Iberian Peninsula corresponds to the Valencia region, where more than one case per year can be recorded by the same observatory (Pérez-Cueva, 1994) and approximately 11 cases per year by all the stations in the Valencia region (Riesco and Alcover, 2003)
The present research confirms the usefulness of the Western Mediterranean Oscillation index (WeMOi) at daily resolution as an effective tool for analysing the occurrence of episodes of torrential precipitation over NE Spain
Summary
The Mediterranean seasonal precipitation regime is characterised by rainy winters and dry summers, linked to the westerly atmospheric circulation in winter and to the subtropical anticyclone belt in summer. Many studies have statistically correlated several teleconnection indices (El Niño–Southern Oscillation, North Atlantic Oscillation, Arctic Oscillation, Mediterranean Oscillation, Western Mediterranean Oscillation, etc.) with precipitation series for the Iberian Peninsula at different timescales (Rodó et al, 1997; Rodríguez-Puebla et al, 2001; Trigo et al, 2004; Lopez-Bustins et al, 2008; González-Hidalgo et al, 2009; Ríos-Cornejo et al, 2015a; Merino et al, 2016) Among these indices, the Western Mediterranean Oscillation (WeMO) was found to be the index most statistically and significantly correlated with annual, monthly and daily precipitation on the littoral fringe of eastern Spain (Martin-Vide and Lopez-Bustins, 2006; González-Hidalgo et al, 2009).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
