Analysis of data for the period 1901-2005 suggests that annual mean temperature for the country as a whole has risen to 0.51oC over the period. It may be mentioned that annual mean temperature has been consistently above normal (normal based on period, 1961-1990) since 1993. This warming is primarily due to rise in maximum temperature across the country, over a larger parts of the data set. However, since 1990, minimum temperature is steadily rising and rate of its rise is slightly more than that of maximum temperature.
Spatial pattern of trends in the mean annual temperature shows significant positive (increasing) trend over most parts of the country except over parts of Rajasthan, Gujarat and Bihar, where significant negative (decreasing) trends were observed.
Season-wise, maximum rise in mean temperature was observed during the Post-monsoon season (0.7oC) followed by Winter season (0.67oC), Pre-monsoon season (0.50oC) and Monsoon season (0.30oC). During the Winter season, since 1991, rise in minimum temperature is appreciably higher than that of maximum temperature over northern plains. This may be due to pollution leading to frequent occurrences of fog.
Upper air temperatures have shown an increasing trend in the lower troposphere, and this trend is significant at 850 hPa level, while decreasing trend (not significant) was observed in the upper troposphere.
All India summer monsoon season (June to September) rainfall as well the rainfall for all the four monsoon months does not show any significant trend.
During the season, three subdivisions viz. Jharkhand, Chattisgarh, Kerala show significant decreasing trend and eight subdivisions viz. Gangetic West Bengal, West Uttar Pradesh, Jammu & Kashmir, Konkan & Goa, Madhya Maharashtra, Rayalaseema, Coastal Andhra Pradesh and North Interior Karnataka show significant increasing trends.
June rainfall has shown significant increasing trend for the western and southwestern parts of the country, whereas significant decreasing trend is observed for the central and eastern parts of the country.
July rainfall has significantly decreased for most parts of the central and peninsular India but has increased significantly in the Northeastern parts of the country.
August rainfall has increased significantly for the subdivisions Konkan & Goa, Marathwada, Madhya Maharashtra, Vidarbha, West M.P., Telengana and west U.P.
September rainfall has shown significantly decreasing trend for subdivisions Vidarbha, Marathwada and Telangana and increasing trend (95%) for the subdivision Sub Himalayan Gangetic West Bengal.
For the North Indian Ocean as a whole, the number of cyclonic and severe cyclonic storms shows a distinct decadal variability.
Long term linear trend (1891-2004) in frequency of tropical cyclones over the north Indian Ocean as a whole, the Bay of Bengal and the Arabian Sea for different seasons, generally, shows a significant decreasing trend. There is sharp decrease in the frequency during the monsoon season.
However, an increasing trend in the frequency of tropical cyclones forming over the Bay of Bengal in the months of May and November, the principal cyclone months, is observed.
Cyclone frequency data for the last four decades (1961 onwards), since when significant monitoring tools like satellite are available, shows a significant decreasing trend for all the months and seasons and once again the maximum decrease was noticed in the monsoon season.