Relief shapes and precipitation on the south side of the Alps Part II: Heavy-rain cases during MAP and sensitivity to topography modifications

Abstract

There are two distinct climatological precipitation maxima on the south side of the Alps and an area of reduced precipitation between them. We tested the impact of meso-beta details of topography on precipitation by simulating 15 cases of heavy precipitation during the Mesoscale Alpine Programme (MAP) special observing period with the MM5 model. Data show that the selected 15 cases are climatologically representative since the precipitation amount for these 15 days shows two climatological precipitation maxima and a drier region between them. We used different idealized topographies of the Alps, as well as the real topography and modifications of the latter at meso-beta scale. The simulations with different idealized topographies show clear influence of supra-regional (scale of some 100 km) convergence upon correct location of the southern Alpine maxima and that the concave terrain shapes at this scale determine the location of the precipitation maxima. The simulations with modified real topography show that (i) in the case of removal of the southwards bulging Trentino Mts. the precipitation maximum concentrates at this modified region; (ii) with removal of the Dinaric Alps the precipitation on the eastern part of the Alps is significantly reduced.