Indian Journal of Geo Marine Sciences Vol. 45 (11), November 2016, pp. 1560-1565 Rainfall variation and frequency analysis study in Dharmapuri district, India V. Rajendran1*, R. Venkatasubramani2 & G. Vijayakumar3 1Department of Civil Engineering,Kathir College of Engineering, Coimbatore, Pin -641062, Tamil Nadu, India. 2Department of Civil Engineering,Sri Krishna College of Technology,Coimbatore, Pin- 641042, Tamil Nadu, India. 3Department of Civil Engineering,Excel College of Technology,Komarapalayam,Pin-637303, Tamil Nadu, India *[E-mail:
[email protected] ] Received 27 April 2015 ; revised 07 May 2015 Thirty two years (1982-2013) daily rainfall data for Dharmapuri District was collected from the TWAD (Tamil Nadu Water Supply and Drainage Board) to analyse the nature of distribution and frequency of rainfall. Average annual rainfall for 32 years data was calculated as 938.1 mm and average annual rainy days were 45.9. Maximum monthly rainfall (197.58 mm) was received during the month of September which was mostly by southwest monsoon. Maximum rainy days were in October (8.6 days). The rainfall received during the winter, summer, southwest and northeast monsoon seasons were 10.5, 181.0, 453.5, 293.0 mm, respectively. Rainfall frequency analysis done by Weibull’s method revealed that the annual average rainfall of 938.1 mm can be expected to occur once in 2.5 years at a probability of 40 %. Monthly dependable rainfall (p>75 %) is expected to occur in every year during the months from September to October. [Keywords:Rainfall distribution; Weibull distribution; Seasonal rainfall: Rainy days; Frequency analysis] Introduction Daily rainfall data for 32 Years (1982 to 2013) In India, about 60 % of total net sown area were collected from the TWAD (Tamil Nadu comes under rain fed lands1.