Pre-monsoon maximum and minimum temperatures over India in relation to the summer monsoon rainfall

Abstract

The pre-monsoon thermal field over the Indian landmass has an important bearing on the land-sea heating contrast in the region, consequently influencing the establishment, advance and overall performance of the Indian summer monsoon rainfall. This paper examines the relationship between the pre-monsoon thermal field over India and the following summer monsoon rainfall, in order to identify possible predictors for long-range forecasting of Indian summer monsoon rainfall. Based on the spatial patterns of correlations of monsoon rainfall with maximum and minimum temperatures at 121 stations well distributed over India, during the recent period 1951-80, two predictors showing a significant contribution to the variance in monsoon rainfall have been identified. They are (i) March minimum temperature in east peninsular India and (ii) May minimum temperature in west central India. These two predictors have performed very well in terms of their significant contribution to the multiple regression models during 1951-1987, vis-à-vis several other known predictors. They have also shown a consistently significant relationship with the monsoon rainfall during the recent period, from the mid-1940s till the end of the data period. A stepwise regression model for long-range forecasting of all-India summer monsoon rainfall, involving three regional predictors, has been developed, and has shown a multiple correlation of 0·89.