Projection of Future Climate over the Koshi River Basin Based on CMIP5 GCMs

Abstract

This paper analyses the climate projections\rover the Koshi river basin obtained by applying the delta method to eight CMIP5\rGCMs for the RCP4.5 and RCP8.5 scenarios. The GCMs were selected to cover the\rfull envelope of possible future ranges from dry and cold to wet and warm\rprojections. The selected coarse resolution GCM outputs were statistically\rdownscaled to the resolution of the historical climate datasets. The scenarios\rwere developed based on the anomaly between the present reference period\r(1961-1990) and the future period (2021-2050) to generate transient climate\rchange scenarios for the eight GCMs. The analyses were carried out for the whole\rbasin and three physiographic zones: the trans-Himalaya, high-Himalaya and\rmiddle mountains, and southern plains. Future projections show a 14% increase\rin rainfall during the summer monsoon season by 2050. The increase in rainfall\ris higher over the mountains than the plains. The meagre amount of rainfall in\rthe winter season is projected to further decrease over both the mountain and\rsouthern plains areas of the basin for both RCPs. The basin is likely to\rexperience warming throughout the year, although the increase in winter is\rlikely to be higher. The highest increase in temperature is projected to be\rover the high Himalayan and middle mountain area, with lower increases over the\rtrans-Himalayan and southern plains areas.