Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

Algorithm for assimilation of SCA observations into a hydrological model

The method of the assimilation of snow cover area (SCA) satellite observations into the hydrological model was developed. The method is based on the correction of the simulations of SCA by hydrological model to agree with the observed SCA.

The hydrological model is improved to simulate the SCA by using the elevation and slope information from the digital elevation model (DEM). The elevation has an effect on both snow accumulation by lower air temperatures and more precipitation on higher elevations and snow melt by delay in melting on higher elevations due to the lower air temperatures. The elevation effect is simulated in the improved hydrological model in order to simulate the spatial variability of the accumulation and melting of the snow cover that allows simulating the snow cover area.

The method of data assimilation in the hydrological model is improved by adding the assimilation procedure of SCA observations to the assimilation of other data (such as discharge, water level and snow water equivalent). The task of data assimilation procedure is to correct the simulation of the hydrological model to agree with all these observations. The SCA observations are used to correct the simulated amount of the snow water storage to agree with the real snow water storage, which is not observable due to the spatial variability of the snow cover properties. Using the SCA observations in the hydrological model is the large step ahead towards the spatially distributed snow cover simulation.

The effect of the SCA observations on the accuracy of the forecasts was tested by making forecasts over spring period with and without SCA observations. The SCA observations were avail-able for the springs 2001-2005.

The observations from springs 2001-2003 were used for the calibration of the model. The data form the spring 2004 was used to test the effect of the SCA observations on the accuracy of the forecasts. The hydrological model was run in two versions with and without using the SCA observations and the simulated flood forecasts were compared. Since spring 2005 the developed method is used in the Finnish operational hydrological forecasting system SYKE-WSFS. The real time flood forecasts are made for the territory of whole Finland, including cross-boundary watersheds, total of 390000km{2}.

Reported by

Finnish Environment Institute
Kesaekatu 6 P.O.Box 140
00251 Helsinki
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