An analytical study was done at Agro Climate Research Centre, Tamil Nadu Agricultural University by using monthly precipitation data for Coimbatore from 1918 to 2017. The collected data was used to compute the seasonal and annual rainfall trend and to study the temporal pattern of drought using Standardized Precipitation Index (SPI). Decadal Precipitation Ratio (PR) was worked out to study the rainfall stability for South West Monsoon (SWM), North East Monsoon (NEM) and annual period. Moderate drought category occurred for nine years during SWM and five years during NEM. Severe drought event occurred for three years during SWM and seven years during NEM. Extreme drought category occurred for one year during SWM and two years during NEM. In 1947, moderate drought was experienced during SWM and severe drought occurred during NEM. In 1952, moderate drought was observed during both the monsoon period. In 2016, severe drought was experienced during both SWM and NEM. Highest The highest PR value of 125 with less than 25 rainy days was recorded for annual rainfall during 2008-2017 which indicated more idiosyncrasy of rainfall.
Key words : SPI,Drought intensity, precipitation ratio, rainfall stability..