Increased flood risk in Indian sub-continent under the warming climate

Millions of people in Indian sub-continent are affected by floods, which have increased during the past decades and likely to increase further in response to warming climate. However, changes in the frequency of floods and associated risks under the warming climate in Indian sub-continent remain largely unrecognized. Using the observations and simulations from Noah-MP land surface hydrological model, we examine the observed and projected changes in extreme precipitation and floods events. A majority of river basins in the Indian-subcontinent experienced a rise in extreme precipitation events during 1966-2005; however, these increasing trends are mostly insignificant at 5% level. Using downscaled and bias-corrected future and historic climate projections from Coupled Model Intercomparison Project (CMIP5) and the Noah-MP model, we show that the frequency of single and multi-day extreme precipitation and flood events are projected to increase substantially in the future over the Indian sub-continental river basins. A significant increase in multi-day (1-5 day) frequency of extreme precipitation and flood events, exceeding return levels based on the historic period (1966-2005), is projected under RCP 2.6 and RCP 8.5 emission scenarios. Our results show that the projected increase in flood frequency can be reduced to half under the low (RCP 2.6) emission scenario in comparison to the high emission scenario (RCP 8.5). More than half of the precipitation extremes result in flood events of 20, 50, and 100 year return periods in the majority of river basins in the Indian sub-continent. Moreover, the multi-day flood events are projected to increase with a faster rate in the future than the single day events, which can have strong implications for agriculture and infrastructure.