ANALYSIS OF SOUTH WEST MONSOON RAINFALL TREND USING STATISTICAL TECHNIQUES OVER NETHRAVATHI BASIN

Abstract

The analysis of rainfall for agricultural purposes must include information concerning the trends or changes of precipitation, the start end and length of the rainy season, the distribution of rainfall amounts through the year and the risk of dry and wet spells. The present study is mainly concerned with the changing trend of rainfall over Nethravathi river basin, located in coastal region of Karnataka state. Nethravathi river originates in the peaks of western ghats and flows towards westwards. The climate over the basin is humid and has large elevation difference varying from 0 to 1400 m above msl. Precipitation trend analysis based on elevation, rain gauge stations were grouped into two regions with similar precipitation characteristics to perform a regional analysis. Daily rainfall data of 40 years from 1971 to 2010 has been processed in the study to find out the monthly variability of south west monsoon (June, July, August, and September) season. Mann-Kendall (MK) test and Sens’s slope estimator has been used to determine trend and slope magnitude. Long-term analysis (1971 to 2010) was carried out for both regions and results have been compared. Monthly precipitation trend has been identified here to accomplish the objective which shows 40 years of data. From the analysis, it is found that there are decreasing trend of precipitation in some months and increasing trend in some other months. The statistical tests which are used in the study are indicative of overall changes in precipitation trend during the south west monsoon.