Climatology of moisture sources fuelling extreme precipitation in the Western Mediterranean region

The Western Mediterranean region (WMR) is usually affected by heavy rainfall, which has been extensively studied in the past because of the enormous impact it causes. However, there is still an open question related to these potentially catastrophic episodes: does the water vapour that feeds precipitation actually come from the Mediterranean Sea? Several studies have pointed to a significant contribution from other moisture sources, but the debate remains open because only a few case studies with disparate findings have been analysed so far. Here we use the Weather Research and Forecasting (WRF) model with a coupled moisture tagging capability to simulate over one hundred cases of extreme precipitation in the WMR. In order to detect possible remote moisture sources, we use a domain that covers almost the entire northern hemisphere. Preliminary results show that, although the contribution from the Mediterranean Sea is crucial, the combined contribution from more distant sources in the tropical, subtropical and north Atlantic is higher on average. In some specific cases, a significant part of the humidity may come from sources as far away as the Pacific Ocean. Our findings suggest that when explaining WMR torrential rainfall episodes, the Mediterranean Sea should be generally understood as a precipitation enhancer rather than the main contributor to precipitation.