The main focus of the study was to reveal the pattern of rainfall trends across different agro ecological sub regions of southern states such as Karnataka, Kerala and Tamil Nadu. For this study seasonal rainfall was used for the analysis and GSUI was used for the analysis and GIS was employed for the spatial distribution of rainfall variability. Study shows that Karnataka and Kerala receive their maximum amount of rainfall during south west monsoon.

Being the wind ward side of Western Ghats mountain, Kerala and western parts of Karnataka experiences maximum amount of rainfall during north east monsoon, mainly due to cyclone tensions in the Bay of Bengal. Kerala and Karnataka also receive copious amount of rainfall during north east monsoon. Annual average trend in rainfall shows that Karnataka receives 862 mm but the maximum annual rainfall of 11052 mm, because the zone KAR6 which receives high rainfall in Karnataka located in Western Ghats region.

Kerala receives an annual average of, 2343.169 mm and maximum annual rainfall of 5869 mm and Tamil Nadu receives 882.9835 mm and maximum annual rainfall of 5846mm.