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An analytical examination was done to work out the unevenness in point location and time to time variability in rainfall at Coimbatore and Erode district of Western agro climatic zone of Tamil Nadu (India) for 100 years (1916-2015). Simple descriptive statistics along with Co-efficient of Variation (CV) were worked to understand the rainfall variability. The long term mean seasonal and annual rainfall analysis showed that South West Monsoon (SWM) rainfall observed was (176.9 mm) & (257.9 mm) and North East Monsoon (NEM) of (336.9 mm) & (323.3 mm) and annual rainfall of (674.8 mm) & (764.4 mm) at Coimbatore and Erode respectively. The CV for seasonal and annual rainfall showed high dependability status by recording appropriate threshold level of CV for seasonal and annual rainfall.

The time series rainfall data for 100 years were divided into ten year period and the correlation was carried out for the SWM and NEM using Spearman’s rank-order correlation. The results indicated the correlation between two monsoons for Coimbatore (0.14) and for erode (0.07) which indicates that there was less relation between SWM and NEM.

Major emphasis was given to analyse annual and seasonal (SWM and NEM) rainfall time sequence over an extensive time gap to identify probable trend and to measure their implication. For Coimbatore and Erode districts, in both the monsoon seasons and annual analysis revealed an increasing trend for long term (100 years-1916-2015) period.