Analysis of Rainfall Trend Using Statistical Techniques Over Manjalar Sub-Basin of Vaigai In Tamilnadu

Precipitation is a principal element of the hydrological cycle and analysis of its temporal variability is important from both the scientific and practical point of view. The annual and seasonal precipitation trends of 13 raingauge stations in Manjalar sub-basin of Vaigai river for the period 1982–2012 were analyzed using the Mann–Kendall test, the Sen's slope estimator and the linear regression. The results indicated an increasing trend in annual precipitation found at three rainguage stations with significant trends observed at the 95% confidence levels. The rate of the significant increasing trends in annual precipitation varied from 10.1 mm/year at Veerapandi station to 9.04 mm/year at Andipatti station. On the seasonal scale, the trends in the South West Monsoon (SWM) and winter season were mostly negative. The highest numbers of stations with significant trends are in North East Monsoon (NEM) while no significant positive and negative trends were detected by the trend tests in winter season. The significant positive trends in seasonal precipitation ranged between 8.81 mm/year at Periyakulam station and 6.49 mm/year at AC&RI, Madurai station in NEM season. The highest and lowest significant increases of precipitation values were obtained over PWD, Madurai and Viralipatti in summer at the rates of 3.11 mm/year and 1.68 mm/year, respectively.