Comparison of two model calibration approaches and their influence on future projections under climate change in the Upp
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Comparison of two model calibration approaches and their influence on future projections under climate change in the Upper Indus Basin Muhammad Fraz Ismail, et al. [full author details at the end of the article] Received: 27 January 2020 / Accepted: 19 October 2020/ # The Author(s) 2020
Abstract
This study performs a comparison of two model calibration/validation approaches and their influence on future hydrological projections under climate change by employing two climate scenarios (RCP2.6 and 8.5) projected by four global climate models. Two hydrological models (HMs), snowmelt runoff model + glaciers and variable infiltration capacity model coupled with a glacier model, were used to simulate streamflow in the highly snow and glacier melt–driven Upper Indus Basin. In the first (conventional) calibration approach, the models were calibrated only at the basin outlet, while in the second (enhanced) approach intermediate gauges, different climate conditions and glacier mass balance were considered. Using the conventional and enhanced calibration approaches, the monthly Nash-Sutcliffe Efficiency (NSE) for both HMs ranged from 0.71 to 0.93 and 0.79 to 0.90 in the calibration, while 0.57–0.92 and 0.54–0.83 in the validation periods, respectively. For the future impact assessment, comparison of differences based on the two calibration/validation methods at the annual scale (i.e. 2011– 2099) shows small to moderate differences of up to 10%, whereas differences at the monthly scale reached up to 19% in the cold months (i.e. October–March) for the far future period. Comparison of sources of uncertainty using analysis of variance showed that the contribution of HM parameter uncertainty to the overall uncertainty is becoming very small by the end of the century using the enhanced approach. This indicates that enhanced approach could potentially help to reduce uncertainties in the hydrological projections when compared to the conventional calibration approach. Keywords Upper Indus Basin . Climatic change . Calibration/validation approaches . Uncertainty
This article is part of a Special Issue on “How evaluation of hydrological models influences results of climate impact assessment”, edited by Valentina Krysanova, Fred Hattermann and Zbigniew Kundzewicz Supplementary Information The online version contains supplementary material available at https://doi. org/10.1007/s10584-020-02902-3.
Climatic Change
1 Introduction River basins in high Asia with mountainous headwaters having seasonal storage in the form of snow and ice are vital because they contribute substantially to the water supply in the densely populated lowlands by forming a natural buffer against drought (Pritchard 2019; Vanham et al. 2008). The Upper Indus Basin (UIB) is one such example that supplies water to the vast Indus plain, often termed the bread basket of Pakistan (Clarke 2015). It plays an important role in feeding the population of 197 million of Pakistan. But this South Asian region is also a hotspot of climate change which will affect the future wate
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