Evaluation of operational hydrological ensemble forecasts in Sweden
Jonas OLSSON
Swedish Meteorological and Hydrological Institute, Norrköping, Sweden
Abstract
A system for hydrological ensemble forecasts has been operational at the Swedish Meteorological and Hydrological Institute since July 2004. It is based on inputs from 50 meteorological ensemble forecasts from the ECMWF. Hydrological ensemble forecasts for 9 days ahead are produced daily for 58 basins in Sweden. All ensemble members, as well as statistics (minimum, 25% quartile, median, 75% quartile and maximum), are stored in a database.
In the presentation, results from an evaluation of the first 1.5 years of poperation will be shown. Evaluation has been performed in both deterministic and probabalistic terms. The deterministic evaluation is focused on a comparison between the ensemble median and the current operational deterministic forecast in terms of bias and RMSE. The probabalistic evaluation investigates the accuracy of the ensemble spread and the performance of discharge threshold exceedance forecasting. Results indicate that the ensemble median performs slightly better than today's deterministic forecast, but that the ensemble spread is too small.
Preliminary and simple tests of how to adjust the ensemble spread will be shown, as will alternative ways to present ensemble forecasts to end users.