The Bavarian Environment Agency uses hydrological models for climate change impact assessments. The sensitivity of these models to the implementation of hydro-power reservoirs is analysed in this study.
The influence of reservoirs on river discharge
The river system in Bavaria is highly managed. Reservoirs are an important method to regulate the flow of a river.
Most of these reservoirs are also implemented in the hydrological WaSiM model, which is used for climate change impact assessments by the Bavarian Environment Agency. But the interaction between the reservoirs and the modeled impact of climate change are not exactly known or quantified.
To better understand the model sensitivity to reservoirs and assess the impact of reservoir (de)construction, the discharge of two Southern Bavarian catchments for the period 1961 – 2016 is modeled with and without artificial reservoirs. The model outputs are compared by analysing statistical characteristics, the behaviour during extreme events and their flow trend based on the Mann-Kendall trend test.
The effect of the reservoirs on the modeled total discharge is small, but the discharge distribution is changed due to the mitigation of high and low discharges. The outputs display falling high flow trends for all examined
gauges and periods and rising low flow trends during the winter half-year. The sign of the trends is not influenced by the deactivation of the artificial reservoirs in the model and the magnitude and significance of the trends only slightly. Flood peaks occur around one to two days earlier and are higher in a model setting without artificial reservoirs.
The results were expected and all results, except the high flow trends, agree with other studies examining observed discharge. A mediocre model performance during extreme events indicates, that the modeling of highly
managed rivers remains a challenge yet to be solved.