Assessing land-surface feedback flux and its drivers during tropical cyclones using Weather Research and Forecasting Model

Abstract Accurate estimation of regional evapotranspiration (ET) is essential for managing water resources of a river basin, which is a challenging task during cyclonic storm events under data-scarce scenarios. For assessing the actual ET using the Weather Research Forecasting (WRF) model, the best working Land Surface Models (LSMs) along with Numerical Weather Prediction modelling was used for a typical tropical Phailin Cyclone event. The suitability of different WRF parameterization scheme combinations (PSCs) were evaluated in the Brahmani River basin in eastern India to reproduce the observed gridded weather variables of 2-m surface air temperature, precipitation and atmospheric pressure at hourly and daily temporal resolutions during the pre-, at-, and post-cyclone events. The results indicate that the ‘Rapid Update Cycle’ (RUC) LSM with ‘Purdu Lin’ microphysics and ‘Arakawa convective’ cumulus scheme performs the best. The 2-m surface air temperature was better simulated than the precipitation during the short timeframe of the extreme event, whereas the overall regional pressure simulation shows a constant bias. As a comparative assessment, the WRF-LSM that accounts for the local and global advection effects, simulated ET flux better than the remote-sensing-based MODIS derived MOD16A2 8-daily dataset and the Food and Agricultural Organization (FAO)-56 Penmen-Monteith (PM) equation. The local feedback of the Phailin cyclone over the land-surface ET flux and its climatic and land-surface drivers (soil moisture) during the pre-, at-, post-cyclone events reveals that the negative Bowen Ratio estimates during the heavy rainfall resulted in a reduced ET flux, wherein the negative sensible heat flux during this period facilitates for flow of heat from surface to atmosphere, cooling the soil of the river basin. Overall, this study aids in a better understanding of the moisture flux and energy transfer dynamics between the land-atmosphere system during the onset of a cyclone.