7th February 2021 Chamoli (Uttarakhand, India) Rock-ice Avalanche: Numerical Model Simulated Prevailing Meteorological Conditions

The present study aims to analyze the high-resolution model-simulated meteorological conditions during the Chamoli disaster, Uttarakhand, India (30.37°N, 79.73°E), which occurred on 7^th February 2021. The Weather Research and Forecasting (WRF) model is used to simulate the spatiotemporal distribution of meteorological variables pre and post-event. The numerical simulations are carried out over two fine resolution nested model domains covering the Uttarakhand region over a period of 2 weeks (2^nd February to 14^th February 2021). The model simulated meteorological variables, e.g., air temperature, surface skin temperature, turbulent heat flux, radiative fluxes, heat and momentum transfer coefficients, specific humidity, and upper wind patterns are found to show significant departure from their usual pattern starting from 72 h until a few hours prior to the Chamoli rock-ice avalanche event. The average 2-m air and skin temperatures near the rock-ice avalanche site 48 h prior to the event are found to be much lower than the average temperatures post-event. The total turbulent heat flux mostly remained downward (negative) throughout 72 h prior to the event and was found to have an exceptionally large negative value just a few hours before the rock-ice avalanche event. Model simulated rainfall and Global Precipitation Measurement Mission (GPM, IMERG) derived rainfall suggest that the part of the Himalayan region falling in the simulation domain received a significant amount of rainfall on 4^th February, ~ 48 h prior to the event, while the rest of days prior and post-event mostly remained dry.