Analysis of the trend of heavy rainfall over Uttarakhand, India

Abstract

Uttarakhand state receives around 79% of the total annual rainfall during the southwest monsoon season, i.e. from June to September. In this study, precipitation data of the monsoon season from 1983 to 2023 of four departmental observatories of the India Meteorological Department (IMD) in Uttarakhand have been used to analyse the trend of frequency of Heavy, Very Heavy and Extremely Heavy rainfall. Tehri & Mukteshwar observatories represent the hilly region of Uttarakhand, while Dehradun & Pantnagar observatories represent the plains of Uttarakhand. Heavy rainfall climatology reveals that the plains of Uttarakhand receive a higher frequency of heavy rainfall days than the hilly stations. The state experiences higher frequency and lower variability of heavy rainfall days during August & July months, followed by September & June. Mann-Kendall non-parametric trend test has been used to evaluate the existence of monotonic trends. The results show a weak, statistically insignificant increasing tendency in the number of heavy and more rainfall days in Dehradun station, while no trend is observed in other stations. Quantitatively, a non-significant rise in the percentage of extreme rainfall to the total monsoon rainfall is observed over Dehradun, Pantnagar & Mukteshwar stations, while Tehri exhibits a non-significant fall in the extreme rainfall quantity. As per the IMD criteria, the 24-hour accumulated rainfall is categorized into Very Light, Light, Moderate, Heavy, Very Heavy & Extremely Heavy. The trend analysis of individual categories of rainfall shows a significant increasing trend in very light rainfall days over three stations (Dehradun, Mukteshwar & Pantnagar) and a non-significant decreasing trend of dry days over three stations (Dehradun, Mukteshwar & Tehri). The other rainfall categories show no trend.