Future climate change: Implications for Indian summer monsoon and its variability

The broad climatological features associated with the Asian monsoon circula tion, including its mean state and intraseasonal and interannual variabilit y over the Indian subcontinent, as simulated in the CCSR/NIES coupled A-O G CM in its control experiment are presented in this paper. The model reprodu ces the seasonal cycle as well as basic observed patterns of key climatic p arameters, in spite of some limitations in simulation of the monsoon rainfa ll. While the seasonality in rainfall over the region is well simulated and the simulated area-averaged monsoon rainfall is only marginally higher tha n the observed rainfall, the peak rainfall is simulated to be about two-thi rds of the observed precipitation intensity over central India. The transient experiments performed with the model following the four SRES 'Marker' emission scenarios, which include revised trends for all the princ ipal anthropogenic forcing agents for the future suggest an annual mean are a-averaged surface warming over the Indian subcontinent to range between 3. 5 and 5.5 degreesC over the region during 2080s. During winter, India may e xperience between 5 and 25% decline in rainfall. The decline in wintertime- rainfall over India is likely to be significant and may lead to droughts du ring the dry summer months. Only a 10 to 15% increase is projected in area- averaged summer monsoon rainfall over the Indian subcontinent. The date of onset of summer monsoon over India could become more variable in future.