2    Methods

The evaluation of the flood forecasting by FFWC will be evaluated by comparing the 3 days and 5 days lead time based forecasting with the observed water level. The water level change during the extreme rainfall from 15 to 17 June at Cherapunjee will be closely monitored upstream of the part of the Meghna basin that resides in Bangladesh. After that, Integrated Vapor Transport (IVT) will be used to detect atmospheric rivers using The Image Processing based Atmospheric River Tracking (IPART) algorithm for the investigation of the association of AR in the generation of AR. Finally, Wind speed and Geo potential Height at 500 hPa pressure level will be plotted for 15 June of 2021 and 2022 to observe the dynamics that differentiate the monsoon onset and the atmospheric river formation.

2.1    Data Collection

The daily accumulated rainfall data of Gauge station at Cherapunjee of June 2022 of the Indian Meteorological Department (IMD) have been used to identify the extreme rainfall. According to IMD, daily accumulated rainfall greater than 204.5mm is considered extreme precipitation. Secondly, the 3 and 5-day forecasted and observed water levels of three BWDB stations (Sylhet, Laurergarh, and Sheola) are collected for the evaluation of the flood forecasting provided by BWDB. Finally, the integrated Vapor Transport (IVT) at 6-hour intervals has been collected from the ERA5 Reanalysis dataset from the European Center of Medium Range Weather Forecast (ECMWF). The integrated Vapor Transport is calculated by the vertical integration of the product of the Specific Humidity and Wind Speed in the Meridian and Zonal Direction in each pressure level from 1000 hPa to 300hPa pressure level. The total IVT is measured by calculating the resultant of the IVT in both the Meridian and Zonal directions. The IVT is calculated using Eq. 1.