Implications of future climate change for event-based hydrologic models

Abstract

Abstract Event-based hydrologic models are frequently used for flood design and assessment. These models generally require the specification of loss values that should relate to antecedent conditions in the catchment. The loss values are key calibration parameters, usually defined by matching model output with recorded or derived streamflow information. It is now widely recognized that climate change will impact the hydrologic cycle and affect catchment conditions. Therefore, loss values calibrated using historical observations may not be appropriate for simulating future flooding. We use the method of bottom-up climate change assessment to understand the potential for future performance changes in a calibrated event-based model due to changing antecedent conditions. This is achieved by comparing the results against those of a continuous hydrologic model that accounts for differences in antecedent catchment storages. We find that event-based model performance diverges substantially from the continuous model results under the climate change scenarios, which account for increased dryness and greater extreme rainfall intensities. The results indicate that there is greater uncertainty in event-based model results when simulating drier climatic states, attributed to greater variability in antecedent conditions. However, when simulating increased extreme rainfall intensity (giving rise to larger rainfall events and generally wetter antecedent conditions), the impact of changing antecedent conditions was less important than the models’ representations of catchment nonlinearity. This suggests that changing antecedent conditions are not always the key source of potential model performance degradation. Therefore, applying continuous simulation will not necessarily offer an advantage in characterizing future floods. This study highlights the uncertainty facing practicing engineers and hydrologists wanting to account for climate change in flood modelling and design. Large scale changes in engineering practice may be required to ensure that the robustness of flood modelling is maintained in a changing climate.