New Delhi: Global warming will result in a rise in extreme rainfall events, increased frequency of cyclones, and more droughts in India over the course of this century, a new government report has said.
The predictions are part of the Ministry of Earth Sciences’ first comprehensive report on how global warming is changing the climate in India, and how climate patterns will shift by the end of this century.
India’s average temperature rose by around 0.7 degree Celsius between 1901 and 2018. It is projected to rise further by approximately 4.4°C by the end of this century, according to the report by researchers from Indian Institute of Tropical Meteorology (IITM), Pune.
This increase in surface temperatures will result in droughts for some regions. It will also intensify rainfall and severe cyclones in others — causing large parts of India to experience floods.
Experts suggest that these changes in climate will have a long term socio-economic impact on the lives of Indians and also affect the country’s relationship with its neighbours.
The report is set to be formally launched Friday.
Rise in temperatures
The report said the temperature rise is largely on account of warming induced by greenhouse gas emissions.
“In the recent 30-year period (1986–2015), temperatures of the warmest day and the coldest night of the year have risen by about 0.63°C and 0.4°C, respectively. By the end of the twenty-first century, these temperatures are projected to rise by approximately 4.7°C and 5.5°C, respectively, relative to the corresponding temperatures in the recent past (1976–2005 average),” the report said.
By the end of this century, the frequency of occurrence of warm days and warm nights is projected to increase to up to 70 per cent.
Meanwhile, the frequency of summer (April–June) heat waves over India is projected to be three to four times higher by the end of the century as compared to the 1976–2005 period.
The average duration of heat wave events is also projected to nearly double.
Sea surface temperature of the tropical Indian Ocean rose by 1°C on average during 1951–2015, which was higher than the global average sea surface temperature warming of 0.7°C over the same period.
Because of the continental ice melt and thermal expansion of ocean water, sea-level in the North Indian Ocean rose at a rate of 1.06–1.75 mm per year during 1874–2004 and accelerated to 3.3 mm per year in the last two and a half decades (1993–2017).
The Hindu Kush Himalayas experienced a temperature rise of about 1.3°C during 1951–2014. Several areas have experienced a declining trend in snowfall and also retreat of glaciers in recent decades. By the end of this century, the annual mean surface temperature over the Hindu Kush Himalayas is projected to increase by about 5.2°C.
More rains, droughts, and frequent severe cyclones
While a rise in temperature leads to an increase in precipitation — since warm air is able to hold more moisture — the summer monsoon precipitation (June to September) over India has declined by around 6 per cent from 1951 to 2015. The decline is particularly notable over the Indo-Gangetic Plains and the Western Ghats, the report said.
It suggests that aerosols released due to human activities have a ‘radiative effect’ forcing some of the energy from the sun to be radiated back into space. This is offsetting the expected rise in precipitation over the Northern Hemisphere.
However, over central India, the frequency of extreme rainfall events — exceeding 150 mm per day — increased by about 75 per cent during 1950–2015.
The overall fall in seasonal summer monsoon rainfall over the last six-seven decades has led to a rise in droughts over India. The extent and frequency of these rose significantly during 1951–2016.
“In particular, areas over central India, southwest coast, southern peninsula and north-eastern India have experienced more than 2 droughts per decade, on average, during this period,” the report stated.
“The area affected by drought has also increased by 1.3% per decade over the same period,” it said.
While the annual frequency of tropical cyclones have reduced notably between 1951 and 2018, the frequency of very severe cyclonic storms during the post-monsoon season increased appreciably during the last two decades (2000–2018).
Climate models project a rise in the intensity of tropical cyclones in the North Indian Ocean basin in this century.
‘Cannot even imagine the impact of this change’
Roxy Mathew Koll, a scientist at IITM Pune and one of the authors of the report, said the threat to human life will get exacerbated if extreme events start overlapping in future, as the report projects.
For example, rising temperatures will mean that severe cyclones will be followed by much heavier rains than before. “Fortunately, Cyclone Nisarga only brushed past Mumbai (this month), but such cyclones would not only cause heavy wind damage but also be followed by heavier rains,” Koll told ThePrint.
“The storm surge shifts waves up the rivers. This would lead to prolonged floods along the river side. On the top of that, there is a rise in sea level too — so the area of inundation gets extended,” he said.
“We are already seeing such events now just with a 0.7°C rise in temperatures. The report projects a rise of around 2.7°C rise — four times of what we are seeing now — by 2040. The impact would be quite large, we cannot even imagine what will happen by the end of the century,” Koll added.
Raghu Murtugudde, a professor at the University of Maryland in US and a visiting faculty at Indian Institute of Technology Bombay, said the impact of the predicted rise in temperatures will need to be looked at in detail by social scientists since the change would impact people very differently in India.
“Over north India, increased pre-monsoon heat waves would impact construction workers and labourers disproportionately,” said Murtugudde, who was also not involved in the study.
In the Bay of Bengal, the rising sea levels due to global warming get combined with the fact that sediments brought down by the rivers flowing from the Himalayas are dumped in the bay. “This results in some parts of Bengal witnessing faster sea-level rise than others,” Murtugudde explained.
Such events would displace people living in coastal areas of not only West Bengal, but also Bangladesh, he said, adding that the socio-economic impact of climate change in neighbouring Pakistan, Nepal and Myanmar would also have implications for India.
“We have to now map the vulnerability of the people to climate change, assessing the impacts from state to state,” he added.