Simulation of Meteorological Conditions Using a High-resolution Model Case Study: Chamoli Rock-Ice Avalanche Event (Uttarakhand, India)

The present study aims to analyze the high-resolution model-simulated meteorological conditions during the Chamoli rock-ice avalanche event, which occurred on 7 February 2021 in the Chamoli district of Uttarakhand, India. Recent changes in climate of the high-altitude Himalayan region have resulted in the formation of numerous water bodies ranging from meltwater ponds to new lakes on the surface of glaciers, while the existing ones are expanding dramatically. 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 February to 13 February 2021). The model-simulated meteorological variables, e.g., air temperature, surface temperature, turbulent heat flux, radiative fluxes, heat and momentum transfer coefficients, specific humidity and upper wind patterns, were found to show significant departures from their usual patterns starting from 72 h until a few hours before the rock-ice avalanche event. The average 2 m air and surface temperatures near the avalanche site during the 48 h before the event were found to be much lower than the average temperatures post-event. This research provides valuable insights into the atmospheric dynamics preceding the event that could potentially be the precursors for the event. This study highlighted the critical role of temperature and precipitation, together with turbulent and radiative fluxes as well as wind speed, in rock-ice avalanche initiation and suggested that the unusual temperature fluctuations, coupled with intense wind and precipitation, could be the primary precursors for the rock-ice avalanche event. In-situ observations and the ERA5-Land dataset also confirm these findings. The total turbulent heat flux mostly remained downward (negative) in the 72 h before the event and was found to have an exceptionally large negative value a few hours before the rock-ice avalanche event. The model-simulated rainfall and Global Precipitation Measurement (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 February, around 48 h prior to the event, while the rest of the days pre- and post-event were mostly dry.. This study explicitly presents out the meteorological conditions that prevailed during, before, and after the rock-ice avalanche event to better understand the weather conditions as a possible triggering factor. Our results may be helpful in further studies to find the possible trigger mechanisms of the event with regards to the freezing and thawing of rock masses.