Rainfall distribution patterns during the monsoon seasons in Vellore district, Tamil Nadu

Abstract

Rainfall is the most critical weather parameter determining agricultural productivity in the semi-arid regions of Tamil Nadu, where the socioeconomic stability of rural communities is intrinsically linked to monsoon behaviour. This study presents a monsoon onset dynamics, temporal distribution, and rainfall intensity over the Vellore district, Tamil Nadu from 2018 to 2024. The results of onset dates reveal the Northeast Monsoon exhibits high synchronization with state-level onset, whereas the Southwest Monsoon shows greater interannual variability and occasional significant delays. Despite these delays, Southwest Monsoon rainfall remained consistently above the normal value (475.3 mm) throughout the study period. In contrast, the Northeast Monsoon displayed extreme fluctuations, ranging from a 22.3% deficit to a 70.3% surplus in 2021, underscoring its dominant yet erratic influence on the region’s hydrology. Weekly and monthly distributions revealed that while light to moderate events predominate both seasons, the northeast monsoon is characterized by high intensity, episodic rainfall, particularly during November (44 to 48^th Standard Meteorological Week). Significant extreme events, such as the 244.2 mm recorded in July 2020 and 179.1 mm in November 2020, highlight a shift toward rainfall extremes post-2020. These findings highlight the Southwest Monsoon provides a stable baseline, the NEM’s high variability, driven by Bay of Bengal cyclonic activity dictates the district's agricultural and water resource success. This temporal rainfall distribution pattern results emphasize the urgent need for adaptive water management and climate-resilient agricultural planning to mitigate the risks posed by increasing rainfall intensity and shifting monsoon behaviour.