This study investigates the rainfall distribution patterns in the Lower Bhavani river basin, analysing annual, seasonal, and decadal variations using long-term daily rainfall data from 18 gauging stations (1981–2019), sourced from the Tamil Nadu Surface and Groundwater Data Centre, PWD, Taramani. The spatial distribution of rainfall across different scales was mapped using the Inverse Distance Weighted (IDW) interpolation method in the ArcGIS environment. The basin’s average annual rainfall is approximately 722.8 mm, which is lower than the state-wide average for Tamil Nadu. The majority of rainfall occurs during the South-West and North-East monsoons, highlighting a pronounced seasonal variability within the basin. The study further identifies years with scanty, deficient, normal, and excess rainfall across different seasons. Decadal analysis shows that the average annual rainfall was 921 mm for the first decade (1981–1990), 936 mm for the second (1991–2000), 614.6 mm for the third (2001–2010), and 643 mm for the last decade (2011–2019). A shift in seasonal rainfall patterns was observed, with the South-West Monsoon dominating the early decade, while a shift towards the North-East Monsoon was noted in the later decades.