Projection of future pluvial flood events over Himalayan river basin under CMIP6 climate data

A hydrological model conceptualizing a certain rainfall event of a watershed is capable of reflecting the hydrological situation and assessing its response not only for historical but also projected climate data in future. This works presents a futuristic flood discharge estimation using the established event based HEC-HMS model corresponding to the meteorological forcing from shared socioeconomic pathways (SSPs) of Coupled Model Intercomparison Project-6 (CMIP6). The hydrological model was setup for flood-prone Himalayan Beas river basin, India. The calibration and validation of the model was carried out for the rainfall induced flooding events of monsoon 2005 and 2010, respectively. The coefficient of determination (R²) and Nash–Sutcliffe efficiency (NSE) were achieved to be 0.82 and 0.79 for calibration and, 0.84 and 0.80 for validation at Bhuntar station, respectively. An improved carbon simulated CMIP6 rainfall data holding of ACCESS-ESM1.5, after bias correction and downscaling, was used to simulate the flood hydrographs in the Beas basin till 2100. The peak discharges of each decade from 2021 to 2100 was estimated and analysed, for the SSP245 and SSP585 scenarios. For the climate projection scenario SSP245, the peak flood event was estimated to be in July 2068 with peak discharge of 4446.7 m³/s while a SSP585 scenario observed extreme flood event in July 2057 having a peak discharge of 4817.2 m³/s. The estimated discharge magnitudes from SSP245 and SSP585 schemes are comparable to the 562 years and 706 years return period discharges of the basin, respectively. The study also revealed that the frequency of flooding events are maximum in the endmost decade of 2091-2100, with an increasing trend towards the later decades.

Keywords: Flood, Hydrological Model, CMIP6, HEC-HMS, Himalayas, Beas river, Climate data