Impact of climate change on flow composition using a model tailored to runoff components

Abstract:

Over the past decades various studies have indicated that climate change and its accompanying hydrological impacts are a prevalent issue. Generally climate change impact on river discharge is assessed on the basis of projected changes in the total runoff. The goal of this research is to gain insight into the runoff components that make up the total runoff and how to calibrate a hydrological model such that the skill with which the individual runoff components are simulated improves. In this study a conceptual precipitation-runoff model HBV is applied to test its ability to model different runoff components. Two different objective functions, one suited for low flow (Nash-Sutcliff based on logarithm of flow) and the other (Nash-Sutcliff on flow) focussing on medium to high flows are used jointly for the model calibration. Those objective functions have assigned weights, varying from 0 to 100%. Using the HBV model that is calibrated for the three case study catchments, climate change impacts on the total runoff have been reassessed and the impact that climate change has on the runoff components and the composition of the runoff are assessed. For climate change (re)assessment synthetic climate data are used from the EURO-CORDEX initiative. The datasets consist of precipitation and temperature simulations generated by seven combinations of General Circulation Models (GCM) and Regional Climate Models (RCM). Assessment of climate change on projected flow resulted in findings that correspond to earlier modelling studies that have used the considered catchments as case studies. The annual total runoff is projected to increase with the largest projected increase observed in the winter (December, January and February) and spring (March, April and May) periods. There appears to be a significant relationship between objective functions that are used in model calibration and the skill at which runoff components can be simulated. This again shows the importance of selecting the most suitable objective functions for the research objective. But even while new insights have been gained in this area it shows that the impacts of climate change on river runoff might be restricted to changes in the total runoff, as the composition of the total annual runoff is not projected to change.