Extreme flows and water availability of the Brahmaputra River under 1.5 and 2 °C global warming scenarios

The recently reached Paris Agreement at the 21st Conference of the Parties (COP21) of the United Nations Framework Convention on Climate Change (UNFCCC) in 2015 includes a goal of pursuing efforts to limit the global warming at 1.5 °C. Following this, the Intergovernmental Panel on Climate Change (IPCC) has accepted an invitation by the UNFCCC to create a special report in 2018 which will include the impacts of 1.5 °C global warming on various Earth systems. It is therefore a priority now for the scientific community to quantify these impacts at regional scales. As a contribution to this effort, this study assesses the impacts of 1.5 and 2 °C global warming on the extreme flows and water availability of the Brahmaputra River, which is both an essential source of freshwater for its lowermost-riparian Bangladesh and also an unavoidable source of disastrous floods. Future flows are simulated with the Soil and Water Assessment Tool (SWAT) and bias-corrected weather data of an ensemble of 11 climate projections from the Coordinated Regional Climate Downscaling Experiment (CORDEX). Results indicate that floods will be more frequent and flood magnitudes greater at 2 °C specific warming level (SWL) than at 1.5 °C SWL. On the contrary, low flows are expected to be less frequent and low flow values to be higher at 2 °C SWL than at 1.5 °C SWL. Water availability will likely be greater at 2 °C SWL than at 1.5 °C SWL from January to August. For the remaining months, water availability will likely be greater at 1.5 °C SWL rather than at 2 °C SWL.