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Zaherpour, Jamal and Gosling, Simon N. and Mount, Nick J. and Müller Schmied, Hannes and Veldkamp, Ted and Dankers, Rutger and Eisner, Stephanie and Gerten, Dieter and Gudmundsson, Lukas and Haddeland, I. and Hanasaki, Naota and Kim, Hyungjun and Leng, Guoyong and Liu, Junguo and Masaki, Yoshimitsu and Oki, Taikan and Pokhrel, Yadu and Satoh, Yusuke and Schewe, Jacob and Wada, Yoshihide (2018) Worldwide evaluation of mean and extreme runoff from six global-scale hydrological models that account for human impacts. Environmental Research Letters, 13 (6). 065015. ISSN 1748-9326

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Abstract

Global-scale hydrological models are routinely used to assess water scarcity, flood hazards and droughts worldwide. Recent efforts to incorporate anthropogenic activities in these models have enabled more realistic comparisons with observations. Here we evaluate simulations from an ensemble of six models participating in the second phase of the Inter-Sectoral Impact Model Inter-comparison Project (ISIMIP2a). We simulate observed monthly runoff in 40 catchments, spatially distributed across 8 global hydrobelts. The performance of each model and the ensemble mean is examined with respect to their ability to replicate observed mean and extreme runoff under human-influenced conditions. Application of

a novel integrated evaluation metric to quantify the models’ ability to simulate timeseries of monthly runoff suggests that the models generally perform better in the wetter equatorial and northern hydrobelts than in drier southern hydrobelts. When model outputs are temporally aggregated to assess mean annual and extreme runoff, the models perform better. Nevertheless, we find a general trend in the majority of models towards the overestimation of mean annual runoff and all

indicators of upper and lower extreme runoff. There are particular challenges associated with reproducing both the timing and magnitude of seasonal cycles; the models struggle to capture the timing of the seasonal cycle, particularly in northern hydrobelts, while in southern hydrobelts the models struggle to reproduce the magnitude of the seasonal cycle. It is noteworthy that over all hydrological indicators, the ensemble mean fails to perform better than any individual model – a

finding that challenges the commonly held perception that model ensemble estimates deliver superior performance over individual models. The study highlights the need for continued model development and improvement. It also suggests that caution should be taken when summarising the simulations from a model ensemble based upon its mean output.

Item Type:	Article
RIS ID:	https://nottingham-repository.worktribe.com/output/938291
Keywords:	global hydrological models, land surface models, human impacts, extreme events, model evaluation, model validation
Schools/Departments:	University of Nottingham, UK > Faculty of Social Sciences > School of Geography
Identification Number:	https://doi.org/10.1088/1748-9326/aac547
Depositing User:	Mount, Dr Nick
Date Deposited:	18 May 2018 11:14
Last Modified:	04 May 2020 19:40
URI:	https://eprints.nottingham.ac.uk/id/eprint/51860

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