Title: A fully coupled atmosphere-hydrology modeling framework to simulate extreme hydro-meteorological event: A case study of Kodagu 2019 flood event over India

Abstract

The adverse impacts of Global Climate change are perceived to be contributing to the increased number extreme weather events like heavy rainfall and floods, thus resulting in loss of lives and properties. In the recent past, many parts of India are witnessing such events. One such event happened over the Kodagu district of Karnataka, India, is considered in this study. The uncertainty associated with the onset-time and the spatial distribution of the heavy rainfall events require an improved understanding of the land-atmosphere feedbacks at higher spatial scales. A well-calibrated, validated, and optimized coupled atmospheric-hydrological modeling system with a very high-resolution can be one of the best tools for the reliable prediction of such events with sufficient lead. The accurate forecast of such hydro-meteorological events go long way in protecting lives and properties of the people. The hydrological module of the WRF-Hydro compensates and strengthens the description of the lateral transport of the infiltration excess process and of the saturated subsurface process in the existing Land surface model (LSM). The fully coupled model is realized by recompiling and merging WRF-Hydro into the mesoscale atmospheric model WRF. The fully coupled WRF- (Hydro/WRF) configuration modulates the spatial distribution of the soil moisture, precipitation, and the evapotranspiration, by means of recycling the surface and subsurface runoff (lateral terrestrial flow). Sensitivity studies involving the land-surface and subsurface feedbacks for a tropical humid region with complex physiographic settings (presence of complex topography) under monsoon regimes (strong synoptic forcing) are lacking. Therefore, in the present study, a fully coupled WRF- (Hydro/WRF) modeling framework with convective permitting grid-scale is used to simulate the hydro-meteorological conditions during an extreme rainfall event (08–09 August 2019). The fully coupled model contributes to a better simulation of the soil moisture content, due to the computation of the lateral redistribution and re-infiltration of the water; the improved simulation of the soil moisture improves the computation of the sensible and latent heat fluxes and thus eventually improves the accuracy the prediction of precipitation.