Countrywide flood forecasting in Scotland: challenges for hydrometeorological model uncertainty and prediction

The Scottish Flood Forecasting Service, a new partnership between the Met Office and the Scottish Environment Protection Agency, aims to make best use of weather and river forecasting expertise in providing improved flood resilience and vigilance for emergency responders across Scotland. Flood guidance employs a blend of experience, professional assessment and input from meteorological and hydrological models. For countrywide forecasts, the CEH-developed Grid-to-Grid model is planned to be the key forecasting tool: it employs rainfall estimates from raingauges, radar and weather models to produce forecast river flows up to 5 days ahead on a 1-km grid across the Scottish mainland. Probabilistic flood forecasts, using ensemble rainfalls as input, are planned in a future phase. Use of rainfall as input to hydrological models is a challenge in Scotland, especially given the terrain and sparse radar and raingauge network coverage, and makes forecasting uncertain. However, the merged hydrological and meteorological capabilities of the new service bring tangible benefits for improved flood forecasting.