A High-resolution Ensemble Run-off Prediction Model for Western Norway

Western Norway is one of the regions with the most precipitation in Europe and is regularly hit by floods. As a result of human-induced climate change the frequency of floods in this region is expected to increase. It is therefore important to have good prediction systems in place in order to predict and mitigate the consequences of future floods. However, the hydrometeorological modelling of Western Norway is complicated because of the complex terrain and weather conditions. This project aims to develop a hydrometeorological ensemble model that is optimized for the Western Norwegian geography and climate. The primary objective of this project is to develop a finite element model based on the discontinuous Galerkin Method with the MEPS meteorological model as meteorological forcing. To obtain a high-resolution model while keeping computational costs relatively low, we employ a coupled 1D–2D hydrological modelling approach. In this model rivers are represented by 1 dimensional channels and the land surface with a 2 dimensional triangular grid, which have a resolution of O(10¹-10²m). As we want to prioritize resources to areas with the most complex topography a higher resolution is used in areas with larger topographic gradients. As the goal is to develop a model that is suitable for real-life forecasting we will utilize the ensemble-Kalman filter for data-assimilation, as this is a very effective method. Hydrological processes such as snow melt and precipitation phase are calculated from simple linear parameterizations, while the infiltration is modelled with the curve number method as these are very efficient and have shown to perform well both in research and in real-life forecasting systems. In the ensemble generation step we take the uncertainties in the meteorological forcing, initial conditions and model parameters into account in order to make the resulting ensembles represent the "real" uncertainty as well as possible. The first test case of the model will be the Gaular water catchment, as it has very good coverage by both hydrological and meteorological measurement stations and was hit by a big flood in 2014. The eventual goal is to extend the model to a larger area of Western Norway.