Diagnosis and numerical simulation of a torrential precipitation event in Catalonia (Spain)

A torrential precipitation event occurred in Catalonia (northeastern part o f Spain) during 9 and 10 October 1994. More than 400mm were registered in t he south of Catalonia. A diagnostic study shows that most of the ingredient s to produce heavy rain (large scale upward vertical motion, instability, h igh moisture content in all the troposphere) were present over the Spanish coast and western Mediterranean. Mesoscale triggering mechanisms have been associated with the orographic forcing, not only through physical lifting o f moist air by the coastal mountains, but also by the redistribution of the surface pressure field induced by the Atlas and Pyrenees ranges. A numeric al simulation of the event using a meso-beta model has been performed. The model forecasts qualitatively well the rainfall distribution but underestim ates the maximum rainfalls. The effects of the orography and the evaporatio n from the sea have been also studied. The simulations have shown that the action of the orography is decisive for the rainfall, pressure and wind dis tributions over the Spanish coast and the western Mediterranean The isolate d action of the evaporation turns to be much less important. However the co mbined effect of orography and evaporation is the most important factor in the areas where the greatest amount of rainfall occurred.