Impact of climate change on floods in the Brahmaputra basin using CMIP5 decadal predictions

Climate change has the potential to intensify the hydrological cycle, leading to more intense precipitation with associated changes in the intensity, frequency and severity of floods. Climate variability and change beyond a few years to a few decades ahead have significant social, economic, and environmental implications. It is believed that some aspects of this decadal variability could be predictable for a decade or longer in advance. Keeping this in mind, phase five of the Coupled Model Intercomparison Project (CMIP5), for the first time, provides 10–30years predictions obtained from the General Circulation Models (GCMs). This study aims to analyse the CMIP5 decadal predictions for precipitation over five sub-basins of river Brahmaputra. Daily precipitation data of five GCMs, namely F-GOALS-g2, BCC-CSM1-1, IPSL-CM5A, CanCM4 and MRI-CGCM3 are used for this assessment. Empirical relationships between the basin averaged rainfall wet spell (storm) properties and the characteristics of the floods are formulated for storms which lead to significant short-term flood response. Following this, the changes in the flood behaviour in the future are derived on the basis of changes in the characteristics of wet rainfall spells in 2010–2020. The results suggest an increase in the number of spells with higher rainfall and longer duration which can lead to increase in peak flood and the total flood volume.