The All-India area-weighted mean summer monsoon rainfall, based on a homogeneous rainfall data set of 306 rain-gauges in India, developed by the Indian Institute of Tropical Meteorology, is widely considered to be a reliable index of summer monsoon activity over the Indian region. The alternating sequences of multi-decadal periods having relatively more frequent droughts and floods can be seen from the figure, which is a characteristic of the well-known epochal pattern of monsoon variability. This figure also associates the rainfall anomalies with El Niño and La Niña occurrences. It can be seen that a majority of the El Niño events are associated with drought years over India, while the La Niña events are associated with flood years.

This figure shows all-india mean series of seasonal and annual surface air temperatures, along with the trend line, based on data during 1901-2000 for a network of 34 stations. The time series indicate a significant warming of 0.3 °C/100 years in the mean annual temperatures of the country as a whole. It can be seen that the post 1940 cooling reported for the Northern Hemisphere is conspicuously absent in the Indian temperatures. It can also be seen that the warming in the annual mean temperatures is mainly contributed by the post-monsoon and winter seasons. The monsoon temperatures do no show significant trend on an all-india scale.

ICRP Bulletin                                              Vol.1 • No.1                                               Page 6