Design Flood estimation based on Equivalent Geomorphological Instantaneous Unit Hydrograph for a Himalayan catchment

Recurrent flood estimation studies in Himalayan catchments located in India are crucial and require abundant monitoring and supervision. Reliable estimation of design floods for mountainous catchments corresponding to various return periods is challenging. Recently, climate change has exacerbated this challenge which pose a serious threat to the water resources within Himalayan region. The Geomorphology based Unit hydrograph theory can provide reliable estimates of design floods for Himalayan catchments. The theory involves determination of Geomorphological Instantaneous Unit Hydrograph (GIUH) corresponding to a catchment and utilizing the GIUH to predict design flood for a design rainfall input. In this study, it is envisaged to model the complex dynamics of floods in a Himalayan catchment by using a modified version of GIUH which is known as Equivalent Geomorphological Instantaneous Unit Hydrograph (E-GIUH). EGIUH overcomes many limitations associated with the conventional GIUH. The application of E-GIUH is performed for Seer catchment which is a sub-basin of Sutlej River basin. The design rainfall input to the E-GIUH is determined from Indian Meteorological Department (IMD) gridded rainfall data for the present (1951-2019) as well as the future time periods (2021-2060 and 2061-2100). Coupled Model Intercomparison Project phase 6 (CMIP6) experiments are considered to determine future projections of rainfall over Seer catchment which are subsequently used to estimate design rainfall input for future time periods. Design flood estimates are obtained for various Shared Socioeconomic Pathways (SSPs), particularly SSP126, SSP245 and SSP585 scenarios from CMIP6 experiments. The geomorphological descriptors used for development of E-GIUH model of the Seer catchment are evaluated using the GIS framework.

Keywords: Climate Change, CMIP6, E-GIUH, IMD, SSP, Seer Catchment