Impact of climate change on the stream flow of the lower Brahmaputra: trends in high and low flows based on discharge-weighted ensemble modelling

Abstract

Abstract. Climate change is likely to have significant effects on the hydrology. The Ganges-Brahmaputra river basin is one of the most vulnerable areas in the world as it is subject to the combined effects of glacier melt, extreme monsoon rainfall and sea level rise. To what extent climate change will impact river flow in the Brahmaputra basin is yet unclear, as climate model studies show ambiguous results. In this study we investigate the effect of climate change on both low and high flows of the lower Brahmaputra. We apply a novel method of discharge-weighted ensemble modeling using model outputs from a global hydrological models forced with 12 different global climate models (GCMs). Our analysis shows that only a limited number of GCMs are required to reconstruct observed discharge. Based on the GCM outputs and long-term records of observed flow at Bahadurabad station, our method results in a multi-model weighted ensemble of transient stream flow for the period 1961-2100. Using the constructed transients, we subsequently project future trends in low and high river flow. The analysis shows that extreme low flow conditions are likely to occur less frequent in the future. However a very strong increase in peak flows is projected, which may, in combination with projected sea level change, have devastating effects for Bangladesh. The methods presented in this study are more widely applicable, in that existing multi-model streamflow simulations from global hydrological models can be weighted against observed streamflow data to assess at first order the effects of climate change for specific river basins.

Impact of climate change on the hydrological regime of the Indus, Ganges and Brahmaputra river basins: a review of the literature

“…The increment in peak flow in the monsoon season is likely to be greater for moderate events and smaller for extreme events with higher return periods. Gain, Immerzeel, Sperna Weiland, and Bierkens (2011) indicated that there will be a strong increase in peak flows, both in size and frequency, although dry-season conditions are likely to increase.…”

Present to future sediment transport of the Brahmaputra River: reducing uncertainty in predictions and management

“…This decrease in melt water was estimated by Immerzeel and van Beek (2010); even though rainfall is projected to increase, they . By the end of the century, however, both mean and extreme discharges are consistently projected to increase in the low-lying Brahmaputra (Gain et al 2011). Estimates for Bangladesh due to projected increases in precipitation range between increases of 13 % (Masood et al 2015) up to 39 % (Darby et al 2015), compared to their respective reference periods both within the years 1980-2000 (Table 1B).…”

Determining critical support discharge of a riverhead and river network analysis: Case studies of Lhasa River and Nyangqu River

“…This study is focused on the CSD related to the discharge in the lower Yarlung Zangbo River Basin, which belongs to the Qinghai-Tibet Plateau where the hydrological impact of climate change is expected to be particularly strong (Immerzeel et al, 2010;Gain et al, 2011). The major meteorological stations of the lower Yarlung Zangbo River are in the eastern and central Tibet in which long-term observed records (precipitation and temperature) are available through the China Meteorological Administration (http://www.cma.gov.cn/en/).…”