Meteorological observations analysis for forewarning of exceptionally heavy rainfall over Himalayan region of India: a case study over Uttarakhand during October, 2021

In India, south-west monsoon winds become weak and monsoon withdraws continuously during October. Rainfall during October is a common phenomenon because October is the transition month from the rainy season to the dry winter conditions. However, occasional rainfall activity continues during October. By the beginning of October 2021, the monsoon withdrew from the northern plains. Uttarakhand experienced exceptionally heavy rainfall, which caused floods and severe damage to the economy and human life in the state from 16 to 20 October 2021. A deep westerly trough lay between longitude 65.0° E to 70.0° E and a low-pressure area observed over east Rajasthan along with moisture incursion from the Bay of Bengal as well as from the Arabian Sea over the western Himalayan region, particularly over Uttarakhand. Moisture incursion from the Arabian Sea is one of the important factor contributing to heavy rainfall. The case study was conducted using various meteorological observations, wind patterns, and weather systems. The current year's rainfall pattern and normal rainfall trend were analysed using rainfall data for October 2021. It is observed that rainfall was received from 13 stations and all the stations of the state received rain heavier than normal during the third week of October 2021, which indicates that exceptionally heavy rain generally, recurved during the third week of October. Actual vs. normal rainfall is showing R2 0.61 which reveals that 61% of the variability observed in the actual variable and is explained by the regression model.