Trends, variability, and teleconnections of long-term rainfall in the Terai region of India

This study examined the long-term (1951-2015) spatio-temporal trends, variability, and teleconnections of rainfall of 15 districts in the Terai region of Uttar Pradesh, India. Gridded rainfall data of the India Meteorological Department (IMD) were analyzed using both parametric and non-parametric approaches, and teleconnections of seasonal and annual rainfall with Indian Ocean Dipole (IOD) and El Nino/Southern Oscillation (ENSO) were investigated. Lag-1 autocorrelation coefficient was calculated and tested at 5% level of significance. Our analysis revealed significantly declining trends in monthly rainfall for most of the districts in all the months, except February, April, May, and December which had increasing trends. Monthly rainfall values of the region as a whole had significantly decreasing trends in January, July, August, and October, while February and April had significantly increasing trends. In seasonal and annual rainfall data, only decreasing trends were significant. Monsoon, post-monsoon, and annual rainfall were decreasing in 6, 9, and 7 districts, respectively. The study area as a whole had a significant decrease in monsoon, post-monsoon, and annual rainfall with significantly negative Sen's slope (- 2.7, - 0.39, and - 3.75), Spearman's rho (- 0.25, - 0.21, and - 0.30), and slope of simple linear regression (- 2.67, - 0.98, and - 3.49). CV for annual rainfall of the whole region was 19% with maximum variability recorded in post-monsoon rainfall (CV = 99.81%). Our results also revealed that the monsoon, post-monsoon, and annual rainfall of the whole region had significant teleconnections with both IOD and ENSO events. The results herein suggests decreasing rainfall trends in the Terai region of India with monsoon and annual rainfall having higher ENSO teleconnections while the post-monsoon rainfall teleconnection, dominated by IOD.