Hydrological forecasting in catchments with glaciers

The runoff forecast is crucial in Norway because the country bases most of its electricity from hydropower. The hydrological model has thus been improved for years in order to foresee the runoff in the best possible way. In Norway, there are many catchments with extensive water storage: glaciers. Those catchments represent a significant part of the catchments where hydropower is produced. Therefore knowing the right amount of outflow from a catchment with glaciers is essential but more challenging. The runoff forecast has been assessed on catchments where the glacier area is decisive for the runoff regime. The catchments chosen are located in Jostedalsbreen, the biggest glacier in Europe, in south Norway. The catchments have specific characteristics in slope, land types etc. which can test the robustness of the hydrological model used, HBV-model. This simple model is not specifically built for glacier behaviour analysis and thus does not include complex calculation on the glacier part. Hence, forecasting runoff with HBV-model for a catchment with glaciers is expected to be arduous. After several trials, two calibrations were done for the two purposes: one strictly hydrological runoff oriented and the other glaciers behaviour related. The simulations were realised in different catchments on a long period of fifty-two years. The concern about the accuracy of the HBV-model to generate a consistent runoff in the catchments selected proved to be unfounded. The first calibration gives so good results in term of runoff that an update of the model for catchments with higher portion with glaciers does not seem necessary. However, to get those results the model passes through calculations which do not fit with what happens in the physical system especially in climatological part and in the snow routine. So the second calibration was realised in order to have routines closer to the physical phenomena. The two different simulation results were then studied for their glacier changes. It appears that both calibrations give reversely extreme glacier mass balances. Therefore, it is difficult to conclude anything for glacier mass balance values in the catchment. After, the climate change in the region was studied to forecast the runoff in the next hundred years. Two different scenarios were evaluated. They give relatively close results in term of the runoff forecast. The glacier mass balances are also close to each other. The scenario A with the highest increase of temperature has stronger impact on the runoff and mass balance of the glaciers. However, it is difficult to conclude on the glacier state at the end of the period with the only two calibrations used, but they will eventually decrease