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Flood hazard is a global problem, but regions such as south Asia, where people's livelihoods are highly dependent on water resources, can be affected disproportionally. The 2017 monsoon flooding in the Ganges-Brahmaputra-Meghna (GBM) basin, with record river levels observed, resulted in similar to 1200 deaths, and dramatic loss of crops and infrastructure. The recent Paris Agreement called for research into impacts avoided by stabilizing climate at 1.5 degrees C over 2 degrees C global warming above pre-industrial conditions. Climate model scenarios representing these warming levels were combined with a high-resolution flood hazard model over the GBM region. The simulations of 1.5 degrees C and 2 degrees C warming indicate an increase in extreme precipitation and corresponding flood hazard over the GBM basin compared to the current climate. So, for example, even with global warming limited to 1.5 degrees C, for extreme precipitation events such as the south Asian crisis in 2017 there is a detectable increase in the likelihood in flooding. The additional similar to 0.6 degrees C warming needed to take us from current climate to 1.5 degrees C highlights the changed flood risk even with low levels of warming.