Frequency analysis of rainfall deviation in Dharmapuri district in Tamil Nadu

Abstract

The 10 years (2004-2013) 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. The average annual rainfall for 10 years data was calculated as 506.78 mm and average annual rainy days was 28.10. The maximum monthly rainfall (264.2 mm) was received during the month of June to September which was mostly by southwest monsoon. The maximum rainy days were in the month of September (15 days). The rainfall received during the winter, summer, southwest and northeast monsoon seasons were 17.16, 97.96, 233.82 and 157.84 mm respectively. Rainfall frequency analysis was done by Weibull’s method reveals that an annual rainfall of 757.55 mm can be expected to occur once in 11 years at a probability of 9.1 %. The monthly dependable rainfall (p>68 %) is expected to occur in every year in the month of September to October.