Projected Climate Change Scenarios over Indian Subcontinent

Climate change is no longer a distant scientific prognosis, but is becoming a reality. Using the UKMO GCM model, Bhaskaran et al. (1995) predicted a total precipitation increase of approximately 20% and an increase in winter or rabi crop season temperature by 1-4°C with increased CO2 concentration. The specific humidity increases by 19%, indicating that the increased monsoon rainfalls were largely due to increased water content of the atmosphere. Greater number of heavy rainfall days during the summer monsoon or kharif period, and an increased interannual variability were predicted. Recently, Lal et al. (2001) estimated larger uncertainty associated with projected rabi rainfall than kharif rainfall in 2050s. The standard deviation of future projections of area-averaged monsoon rainfall centered around 2050s was not significantly different relative to the present-day atmosphere, implying thereby that the year-to-year variability in mean rainfall during the monsoon season might not significantly change in the future. More intense rainfall spells were, however, projected over the land regions of the Indian sub-continent in the future, thus increasing the probability of extreme rainfall events in a warmer atmosphere.

Rupakumar and Ashrit (2001) projected an increase of 13% in monsoon or kharif season rainfall in India using ECHAM4 model, while HadCM2 model suggested a reduction in kharif rainfall by 6% due to the greenhouse gas simulation. Both GCMs suggested an increase in annual mean temperature by more than 1°C (1.3°C in ECHAM4 and 1.7°C in HadCM2). Rupakumar et al. (2003) concluded that the coupled models indicated general warming and enhanced rainfall conditions over India towards the later half of the 21st century, in a GHG increase scenario; however, there was some disagreement among the models on rainfall changes, with respect to decreases in rainfall in some states (viz. Jammu and Kashmir, Himachal Pradesh, Bihar, Gujarat and Rajasthan etc.). May (2002) predicted an intensification of rainfall in Indian region during monsoon season as a consequence of the anticipated increases in the greenhouse gas concentrations.

The increase in the regional rainfall was found to be related to an intensification of the atmospheric moisture transport into the Indian region. Stephenson et al. (2001) observed a weakening of the large scale aspects of the Indian summer monsoon. Rupakumar et al. (2003) concluded that under future scenarios of increased greenhouse gas concentrations (GHG), there would be marked increases in both rainfall and temperature into the 21° century, which will become more conspicuous after 2040s in India. Over the region south of 25°N (south of cities, such as Udaipur, Khajuraho and Varanasi), the maximum temperature would increase by 2-4°C during 2050s. In the northern region, the increase in maximum temperature might exceed 4°C, which might exceed over the southern peninsula, northeast India and some parts of Punjab, Haryana and Bihar.

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