Observed Variability and Long-Term Trends of Rainfall Over India

Abstract

Long-term (1901–2010) district data have been used to examine the observed variability and trends in rainfall during the south-west monsoon season (June–September) and north-east monsoon season (October–December) over India. South-west monsoon rainfall averaged over the country as a whole does not show any significant long-term trend during the period 1901–2010, suggesting that south-west monsoon system is stable. However, there is a significant multi-decadal epochal variability over the country and the four homogenous regions over India. The recent decades from 1971 onwards are found to be drier than normal with the recent decade 2001–2010 being the driest. Rainfall during the month of July shows a decreasing trend over most parts of the central India. However, rainfall during June and August shows increasing trend over the central and south-western parts of the country. Significant decreasing trends are observed in the seasonal rainfall over three subdivisions, and significant increasing trends are observed over eight other subdivisions. The analysis of the north-east monsoon (October–December) rainfall over the five met-subdivisions of Peninsular India reveals no significant long-term trend. However, the presence of decadal variability in north-east monsoon rainfall is clearly observed.