Rainfall variability and its association with El Niño Southern Oscillation in Tons River Basin, India

In this study, rainfall variability in connection with El Niño Southern Oscillation (ENSO) over the Tons River Basin which is a sub-basin of the Ganges River has been examined. The rainfall trends on annual and seasonal basis for 15 weather stations were examined using the data of 1951–2004. Furthermore, the association between ENSO and rainfall was analyzed using three methods, namely cumulative frequency distributions, correlation analysis, and composite analysis. The annual rainfall series analysis indicated a significant decrease at Govindgarh (5.5 mm/year) and Meja (6.6 mm/year) stations. Seasonal rainfall analysis indicated significant decreasing trends at fourteen stations in pre-monsoon season, ten stations in winter season, two stations in post-monsoon, and only one station in monsoon season. The average frequency of occurrence of drought is once in every 4–7 years. Only monsoon season rainfall showed a significant negative correlation with Niño 3.4 SST at almost all the stations. During El Niño, the probability of below normal rainfall is high. However, during La Niña, the probability of above normal or near normal rainfall is high in monsoon season. Furthermore, comparison of results before (Pre76) and after (Post76) the climate shift revealed that the relationship between rainfall and El Niño has strengthened after the climate shift.