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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 06 Feb 2019

Submitted as: research article | 06 Feb 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Hydrology and Earth System Sciences (HESS).

Does the weighting of climate simulations result in a more reasonable quantification of hydrological impacts?

Hui-Min Wang1, Jie Chen1, Chong-Yu Xu1,2, Hua Chen1, Shenglian Guo1, Ping Xie1, and Xiangquan Li1 Hui-Min Wang et al.
  • 1State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wuhan, 430072, China
  • 2Department of Geosciences, University of Oslo, Oslo, Norway

Abstract. With the increase in the number of available global climate models (GCMs), pragmatic questions come up when using them to quantify the climate change impacts on hydrology: Is it necessary to weight GCM outputs in the impact studies, and if so, how to weight them? Some weighting methods have been proposed based on the performances of GCM simulations with respect to reproducing the observed climate. However, the process from climate variables to hydrological responses is nonlinear, and thus the assigned weights based on their performances in climate simulations may not be translated to hydrological responses. Assigning weights to GCM outputs based on their ability to represent hydrological simulations is more straightforward. Accordingly, the present study assigns weights to GCM simulations based on their ability to reproduce hydrological characteristics and investigates their influence on the quantification of hydrological impacts. Specifically, eight weighting schemes are used to determine the weights of GCM simulations based on streamflow series simulated by a lumped hydrological model using raw or bias-corrected GCM outputs. The impacts of weighting GCM simulations are investigated in terms of reproducing the observed hydrological regimes for the reference period (1970–1999) and quantifying the uncertainty of hydrological changes for the future period (2070–2099). The results show that when using raw GCM outputs with no bias correction, streamflow-based weights better represent the mean hydrograph and reduce the bias of annual streamflow. However, when applying bias correction to GCM simulations before driving the hydrological model, the climate simulations become rather close to the observed climate, so that compared to equal weighting, the streamflow-based weights do not bring significant differences in the multi-model ensemble mean and uncertainty of hydrological impacts. Since bias correction has been an indispensable procedure in hydrological impact studies, the equal weighting method may still be a viable and conservative choice for the studies of hydrological climate change impacts.

Hui-Min Wang et al.
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Status: final response (author comments only)
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Hui-Min Wang et al.
Hui-Min Wang et al.
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Short summary
When using large ensembles of global climate models in hydrological impact studies, there are pragmatic questions on whether it is necessary to weight climate models and how to weight them. We use 8 methods to weight climate models straightforward based on their performances on hydrological simulations, and investigate the impacts of the assigned weights. This study concludes that the equal weighting method is still a viable and conservative method for the bias-corrected climate model ensembles.
When using large ensembles of global climate models in hydrological impact studies, there are...