Anomalous behavior of Indian summer monsoon in the warming environment

The variability of Summer Monsoon (SM) rainfall over India using the gridded rainfall data as well as subdivisional rainfall data is studied for the period 1951-2008. The total length of period is divided into two parts, 1951-1969 (Pre-Global Warming (PGW) period) and 1970-2008 (Global Warming (GW) period) as the Earth shows rise in the temperature since the beginning of 1970s. The differences in the mean rainfall of these two periods are tested using the Z-statistic. Further, the mean zonal wind differences at different grid-points at 850 hPa and 150 hPa of the above two periods for the domain 30°E-120°E, 40°S-40°N are calculated and tested using the Z-statistic. The results indicate that the reduced rainfall activity over India in the global warming is associated with a weakened SM system. Next, the differences in the frequencies of the days having different limits of rainfall are obtained by subtracting the frequencies of the PGW period from those of the GW period. The results pinpoint an increase in the no rainfall (dry) days as well as the extreme rainfall events in the warming environment.