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Ann. Geophys., 21, 627-637, 2003
www.ann-geophys.net/21/627/2003/
© European Geosciences Union 2003
On ALADIN precipitation modeling and validation in an Alpine watershed
B. Ahrens1, K. Jasper2, and J. Gurtz2
1Institute for Meteorology and Geophysics, University of Vienna, Austria
2Institute for Atmospheric and Climate Research, ETH Zürich, Switzerland
Abstract. Highly resolved
precipitation forecasts are necessary in many applications, especially in
mountain meteorology and flash flood forecasts for small- to medium-sized
alpine watersheds. Here we present precipitation forecasts simulated by the
limited area model ALADIN applying different grid resolutions (Dx
= 10 km and 4 km). Target area of the investigations is the Alpine
Ticino-Verzasca-Maggia watershed (total area: 2627 km2). We discuss
problems of validation of high-resolution precipitation forecasts by comparison
with observed precipitation fields and apply an indirect validation approach by
using ALADIN forecasts as input to hydrologic simulations. These simulations
are carried out with the distributed hydrologic model WaSiM-ETH (Dx
= 500 m, Dt = 1 h). The time step of meteorological
input to WaSiM-ETH is fixed at 1 h but spatial resolution varies. The main
result of the validation experiments for three heavy precipitation events is,
that coarser-scale ALADIN forecasts (in model version 11.2) provide better
precipitation predictors for hydrologic modeling than higher-resolution
forecasts. The experiments demonstrate that hydrologic modeling is a promising
tool for the evaluation of high-resolution precipitation fields.
Key words. Hydrology (floods) –
Meteorology and atmospheric dynamics (mesoscale meteorology; precipitation)
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