Performance assessment of the semi-distributed hydrological model HYPE for central Norway

Abstract

Norway s water authorities need a comprehensive tool to generate hydrological infor- mation for all water bodies to implement the European water framework directive. The precipitation-runoff model HYPE was developed by the Swedish meteorological institute SMHI. In Sweden, it is used for flood forecasting, characterization of water body status and establishment of environmental goals. The model structure and the spatial assignment system of hydrological properties makes it suitable for predictions in ungauged catchments. The main question for this thesis was to evaluate, if the semi-distributed model is a suitable simulation framework for Norway and if predictions for ungauged catchments are of satisfying accuracy. HYPE was applied and tested for Norway. The model was set up for a region of 81,900 km 2 in central Norway and divided into ∼ 2500 sub-catchments. National data bases for land use and soil types were combined to assign physiographical attributes to sub-catchments. 40 streamflow stations were implemented, the discharge time series of ten stations were used for calibration, validation and regionalization. HYPE was calibrated using a multi-basin approach, i.e. it was not calibrated to individual stations but for optimal performance across a selection of five stream flow stations. Their respective drainage areas are unregulated and range in size from 100 km 2 to 3000 km 2 . The model fitness was assessed with split-sampling for a period of five years. Kling-Gupta-efficiency (KGE) was applied as index of model performance. The regional calibration resulted in a mean KGE of 0.73 and 0.71 for the calibration and validation period respectively. The model configuration was transferred to five independent proxy catchments with comparable catchments characteristics. The model yielded a mean KGE of 0.49 for the selected regionalization catchments. The regionalization was expanded to all implemented gauges, resulting in a mean KGE of 0.51. Performance assessment of the ungauged catchments show a high variance in model fitness.