Methodology/work description :
The Radar, NWP forecasts, raingauge and satellite data are used to estimate rainfall fields from which areal rainfall is calculated. The estimates from the different sources are compared with a "baseline" estimate in terms of (i) total rainfall amounts (ii) spatial pattern and correlation structure. At Partner 4 the "baseline" will be the existing meso-scale analysis procedure. At Partner 9 the "baseline" will be a stochastic model, based only on previous rainfall which represents the best that can be achieved without concurrent measurements or telemetry. At Partner 2 the "baseline" will be represented by the identification of a Kriging model using past rain-gauge rainfall data. Spatial anomaly patterns will be identified for each source of estimates and compared with physical features of the catchment, e.g. its orography in the case of radar and raingauges or characteristic scales of the numerical model in the case of NWP.
Rainfall estimation fields from the 5th Framework Programme Project EURAINSAT (EVG1 CT-2000-00030) will be provided by Partner 8 as a contribution to the workpackage. Satellite-derived fields are particularly suited for this purpose given their space-time repetition. In particular the MSG-derived rainfall, which represents a key product of EURAINSAT, will be upgraded every 15 min. The bias of satellite rainfall fields, however, is expected to be higher than that of other sources. The trade-off between effective coverage and low bias is thus to be carefully checked in terms of the desired output, especially for flood monitoring and forecasting.
For each source, the rainfall estimates will be used to drive an hydrological model to verify their adequacy in both estimating and forecasting catchment runoff. In the case of Partner 4 will be used a the state of the art semi-distributed model. In the case of the smaller Partner 9 catchment, both the simpler lumped models (both catchment models and unit hydrographs) and the more complex distributed models (already developed at Partner 2) will be used. In all cases a comparison of the estimated with the measured floods will be used to assess any systematic areal bias in the precipitation estimates.
At partner 9, a Monte-Carlo stochastic procedure will be used to assess the sensitivity of distributed catchment models to the observed patterns of bias, spatial and temporal variability. Models of different complexity will be used, to investigate any relationship between model complexity and sensitivity to errors in the inputs Lumped catchment models will be compared with a fully distributed physically based model. A large number of realisations of forecast error patterns will be generated and the outflows from the models calculated. A detailed statistical analysis of the errors in these will be undertaken.
Basic minimum useful accuracy tolerances for the flood peak will be established in consultation with the end-user group.