Impact of precipitation disparity on groundwater fluctuation in a semi-arid region (Vellore district) of southern India using geospatial techniques.

In the present study, impact of precipitation disparity on groundwater level fluctuation was carried out in Vellore district, Tamil Nadu, India, using geospatial techniques. There are five rain gauge stations in the study area in which three rain gauge stations, namely Alangayam, Jolarpettai and Pernampet, receive more precipitation when compared with the average annual precipitation of Tamil Nadu state (920 mm). The other two stations, namely Madanur and Natrampalli, receive less than 920 mm of precipitation annually. The overall average annual precipitation of the study area is 913.6 mm. More than 100 mm precipitation is received in all the five rain gauge stations during southwest (SW) and northeast (NE) monsoon seasons. The maximum monthly precipitation is usually recorded during the month of November and the minimum precipitation is recorded during June. The post-monsoon precipitation is around 10.8 mm, which is almost negligible in the study area. The contribution of precipitation by various seasons is in the following sequence: Southwest monsoon > Northeast monsoon > Pre-monsoon > Post-monsoon. The spatial disparity study indicates that the intensity of average annual, pre-monsoon and post-monsoon precipitations increase towards west in the study area. The intensity of precipitation is more in the northern part during SW monsoon season, whereas the intensity is more in the southern part during NE monsoon season. The spatial disparity analysis of groundwater fluctuation shows that the depth of groundwater (below ground level) increases towards west during all the monsoon seasons. The minimum, mean and maximum depths of occurrence of groundwater in this region are, respectively, 1.6, 9.6 and 21.15 m. Declining trend in the regional groundwater level is observed from December to June because of less precipitation during non-monsoon season. However, the monsoon (both SW and NE monsoon) precipitation recharges the groundwater from June to December to reach the maximum in the month of December.