Indian summer monsoon rainfall indices : 1871-1990

Abstract

The paper describes some homogenous representations of the Indian summer monsoon rainfall for the period 1871-1990, prepared on the basis of a fixed and well-distributed network of 306 rain-gauges. An Indian Summer Monsoon Rainfall (ISMR) Index, indicating the net excess of deficient rainfall conditions over the country, is proposed. Statistical analysis of the above series identifies 18 large-scale dry years and 15 large-scale wet years during the last 120 yr. The decadal means of ISMR index were continuously negative for three decades 1901-30, positive 1931-60 and again became negative during the current period 1961-90.