Ensemble catchment hydrological modelling for climate change impact analysis

The influence of hydrological model structure on the model performance for catchment runoff, including high and low flow conditions, was investigated by an ensemble of five hydrological models with different spatial resolutions and process descriptions. This was done for a selected catchment in Belgium. The selected models cover a wide set of model complexities: from the lumped conceptual models NAM, PDM and VHM, over the intermediate detailed and distributed model WetSpa, to the highly detailed and fully distributed model MIKE-SHE. The latter model simulates next to the catchment runoff also internal discharges and groundwater heads. In order to obtain consistent and reliable models for use in water engineering (design) applications or scenario-based impact assessment, all models were consistently calibrated by a given systematic but time demanding calibration protocol. The protocol relies on information of runoff subflows and various types of runoff responses derived from the observed river flow, rainfall and potential evapotranspiration (ETo) time series. Explicit focus was given to the high and low flow extremes. It is shown that all models are able to produce reliable estimates of the flow regimes under the current climate, also for the extreme peak and low flows. They are also able to simulate well the changes in quick runoff coefficient under changing rainfall intensities. Next, intercomparison was made of the simulated impact of climate scenarios. Climate scenarios were developed for rainfall and potential evapotranspiration (ETo), tailored for the impact assessment of runoff extremes (peak and low flows). The tailoring process involved assessment of the hydrological impacts of the climate change signals from all available climate model simulations using a quantile perturbation approach and the hydrological models. The high, mean and low impacts were identified and corresponding rainfall and ETo change factors were back-tracked on a seasonal basis to determine rainfall–ETo covariation. This covariation was a useful guide in constructing the tailored scenarios. After simulation of these climate scenarios in the five hydrological models, close agreement was found among the models on the expected hydrological changes. The different models predict similar range of peak flow changes. For the low flows, the differences in the projected impact range by the different hydrological models is larger, particularly for the drier scenarios. Results suggest that the hydrological model structure is very critical in low flow predictions, more than in high flow conditions. Given that it is difficult to make definite statements on the accurateness of the extreme flow and flow change results of individual models, it is concluded that a multi-model ensemble approach where different plausible model structure are applied, is extremely useful, and allows decision making to be based on uncertainty assessment that includes model structure related uncertainties. The study also highlights the importance to pay more attention to model parameter calibration in climate impact assessment studies. A calibration strategy using subflow information and considering model performance evaluation of peak and low flow extremes, does not only guarantee a good overall performance of total runoff flows, but also of the individual model components and the hydrological extremes. Albeit hard to test, it is expected that this additional testing improves the reliability of climate change impact results on these extremes and flow components, where the accuracy of the slow flow component simulation plays an important role for the low flow impact analysis; idem for the quick flow component and the peak flow impact results. The flow impact results are indeed fully controlled by the internal mechanistic structures of the models. References: Ntegeka, V., Baguis, P., Roulin, E., Willems, P., 2014. Developing tailored climate change scenarios for hydrological impact assessments. Journal of Hydrology, 508C, 307-321 Vansteenkiste, Th., Tavakoli, M., Ntegeka, V., Willems, P., De Smedt, F., Batelaan, O., 2013. Climate change impact on river flows and catchment hydrology: a comparison of two spatially distributed models. Hydrological Processes, 27(25), 3649-3662 Vansteenkiste, Th., Tavakoli, M., Ntegeka, V., Van Steenbergen, N., De Smedt, F., Batelaan, O., Pereira, F., Willems, P., 2014. Intercomparison of five lumped and distributed models for catchment runoff and extreme flow simulation. Journal of Hydrology, 511C, 335-349 Vansteenkiste, Th., Tavakoli, M., Ntegeka, V., De Smedt, F., Batelaan, O., Pereira, F., Willems, P., 2014. Intercomparison of climate scenario impact predictions by a lumped and distributed model ensemble. Journal of Hydrology, in revision.

Publication year:2014

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