Some evidence of climate change in twentieth-century India

Abstract

The study of climate changes in India and search for robust evidences are issues of concern specially when it is known that poor people are very vulnerable to climate changes. Due to the vast size of India and its complex geography, climate in this part of the globe has large spatial and temporal variations. Important weather events affecting India are floods and droughts, monsoon depressions and cyclones, heat waves, cold waves, prolonged fog and snowfall. Results of this comprehensive study based on observed data and model reanalyzed fields indicate that in the last century, the atmospheric surface temperature in India has enhanced by about 1 and 1.1°C during winter and post-monsoon months respectively. Also decrease in the minimum temperature during summer monsoon and its increase during post-monsoon months have created a large difference of about 0.8°C in the seasonal temperature anomalies which may bring about seasonal asymmetry and hence changes in atmospheric circulation. Opposite phases of increase and decrease in the minimum temperatures in the southern and northern regions of India respectively have been noticed in the interannual variability. In north India, the minimum temperature shows sharp decrease of its magnitude between 1955 and 1972 and then sharp increase till date. But in south India, the minimum temperature has a steady increase. The sea surface temperatures (SST) of Arabian Sea and Bay of Bengal also show increasing trend. Observations indicate occurrence of more extreme temperature events in the east coast of India in the recent past. During summer monsoon months, there is a decreasing (increasing) trend in the frequency of depressions (low pressure areas). In the last century the frequency of occurrence of cyclonic storms shows increasing trend in the month of November. In addition there is increase in the number of severe cyclonic storms crossing Indian Coast. Analysis of rainfall Climatic Change (2007) 85: amount during different seasons indicate decreasing tendency in the summer monsoon rainfall over Indian landmass and increasing trend in the rainfall during pre-monsoon and post-monsoon months.

Trends in Rainfall and Peak Flows for some River Basins in India

“…Analysis of seasonal rainfall showed a decreasing trend in the monsoon season over India and increasing tendency during the pre-and post-monsoon months. Dash et al 5 and Kumar et al 4 did not find any significant trend in annual, seasonal and monthly rainfall. Interestingly, they observed decrease in annual and monsoon rainfall, and an increase in pre-monsoon, post-monsoon and winter rainfall over the years, on trend analysis using rainfall data for the country for 135 years (1871-2005); however, maximum increase in rainfall was observed during the pre-monsoon period.…”

“…No clear trend was observed while analysing the long period monsoon rainfall data particularly on all India scale. Some studies identified pockets of significant long-term rainfall changes 2,5,6 . Ramesh and Goswami 7 analysed daily gridded observed rainfall data for the period and found that the number of rainy days showed a decreasing trend.…”

“…Many studies have reported that there is increase in frequency of intense rainfall events, but the total annual precipitation and the number of rainy days have decreased in many parts of Asia 5,[14][15][16][17][18][19] . Increase in extreme rainfall events may have led to severe floods and landslides.…”

Climate Change in the Himalayas: Current State of Knowledge

“…They report that much of this observed trend is related to increases after Although, studies specific to the eastern Indian Himalaya are not available in the literature, many of the studies discussed above include the eastern Indian Himalaya as part of the greater northeast Indian region. For 1901-2003, Dash et al (2007 found a rise in Tmax of 1°C over the whole northeast India. The study reports annual average daily minimum temperature The Nepalese Himalaya also saw a warming trend in the last century.…”

“…In a very recent regional study using Climate Research Unit's reconstructed temperature dataset (Brohan et al, 2006), Diodato et al (2011) show that in the last few decades the Himalayan and Tibetan Plateau region have warmed at a rate higher than that in the last century. They show a 0.5 °C in annual average maximum temperature (Tmax) warming over 1971compared to 1901-1960. Dash et al (2007 report that the western Indian Himalayas saw a 0.9 °C rise over 102 years .…”