Abstract

Time series rainfall data from Cotton Research Station, Tamil Nadu Agricultural University, Srivilliputtur, Virudhunagar District of Southern Tamil Nadu for the period of 26 years (1987 to 2012) had been collected and analysed for Standard Deviation (SD) and Coefficient of Variation (CV). The initial probability analysis was also worked at 30, 50 and 75 per cent level for weekly, monthly and seasonal rainfall. The results revealed that the North East Monsoon (NEM) season contributed the highest of 53.8 per cent to annual rainfall (818.8 mm) followed by summer and South West Monsoon season (SWM). The CV values were within 50 per cent for NEM and SWM indicating the higher dependability of rainfall. The CV values for April, May, August, September, October and November are lesser than the critical level of 100 per cent indicating lesser variability and higher dependability of rainfall than other months. The chance of getting mean seasonal rainfall for the SWM, NEM and summer seasons is once in alternate years. The monthly probability analysis indicated that the 50 per cent probability rainfall was almost equal to that of mean monthly rainfall during October and November only. The 50 per cent chance of receiving more than 20 mm rainfall was observed during the meteorological standard weeks from 41 to 47. The possibility of receiving more than 30 mm at 75 per cent probability level was noticed only during 44 and 45th standard weeks.

Keywords: Rainfall probability, Variability, Semi arid region, Tamil Nadu