High resolution distributed atmospheric-hydrological modelling for Alpine catchments

When global climate scenarios are dynamically downscaled to catchment scale or when improvements of short term flood forecasts are discussed, the basic question arises: how reliable do meteorological models reproduce meteorological fields? Can they be used for driving hydrological models? Apart from this, meteorological modelling may facilitate hydrological modelling efforts when no or little meteorological station data is available. Against this background we performed coupled high resolution meteorological-hydrological simulations for the alpine and orographic complex catchment of the river Mangfall (State of Bavaria, Germany). The area of the catchment is around 1100 km2. Within this task we coupled (in 1-way manner) the mesoscale meteorological model MM5 with the distributed hydrological model WaSiM. The hydrological model was calibrated at 18 gauges using interpolated meteorological station data and applied in 150×150 m2 horizontal resolution. Global reanalyses were dynamically downscaled with MM5 from 100×100 km2 resolution to 2×2 km2 using four nests. The quality of the meteorological model was analysed by comparison to upper air and surface observations. A height dependent bias between station-based and MM5-based simulation was observed: the MM5-based interpolation of precipitation yielded 21% less total yearly precipitation in the catchment compared to the station-based interpolation (1446 vs. 1791 mm). Even though not all details of observed runoff were met by the coupled meteorological-hydrological simulations, it is demonstrated that in general observed runoff was reproduced reasonable for the period investigated (1997). Difficulties to describe observed runoff during snow-accumulation and snow-melt processes were observed in both the 'station-based' and coupled simulations.