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Coupled runoff simulations as validation tools for atmospheric models at the regional scale

High‐resolution atmospheric forecasting systems are characterized by an increasing complexity which renders validation and interpretation of the model results more and more demanding. This is especially evident in complex terrain. In such areas, the limited density of meteorological observing stations does not allow an accurate evaluation of high‐resolution weather forecasts. Accordingly, advanced tools for the validation of atmospheric models are necessary and of great interest to forecasters. In this paper we address this issue, and present the possibilities and advantages offered by coupling atmospheric and hydrological models. A distributed hydrological model has been used to estimate the forecast quality of two different weather prediction models at different resolutions for the mesoscale Ticino–Verzasca–Maggia watershed, a high catchment located in the southern European Alps draining from the north into the Lago Maggiore. For this area, several hydrological forecast‐driven model experiments have been carried out as one‐way nested simulations using hourly time steps and 0.5 × 0.5 km grid resolution. The availability of meteorological forecast sequences allowed continuous atmospheric– hydrological simulations covering non‐overlapping periods of 3.5 years and 2.5 months. The model results have been analysed using multiple comparisons including rainfall and runoff measurements, as well as observation‐driven model results of river runoff and water balances at the catchment‐scale. It is shown that the hydrological model is sufficiently sensitive to provide substantial information for the validation of atmospheric models. Copyright © 2003 Royal Meteorological Society.