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Extreme rainfall in India may be owing to greenhouse emissions, finds study

The study has implications for infrastructure, agriculture and water resources, is important because India has seen a rise in extreme rainfall events over the last decade.

mumbai Updated: Mar 29, 2018 09:43 IST
Snehal Fernandes
Snehal Fernandes
Hindustan Times
Greenhouse gases increase extreme rainfall events by 10% to 30%. (HT File/Representational Image )

Greenhouse emissions from human activities play a significant role in extreme rainfall events across India, says a study by the Indian Institute of Technology – Gandhinagar (IITGn) and US-based Lawrence Berkeley National Laboratory.

The study has found that greenhouse gases emitted by industries, vehicles, biomass burning and deforestation — also called anthropogenic or man-made emissions — increase extreme rainfall events by 10% to 30%. Greenhouse gases include carbon dioxide, methane, nitrous oxide and other gases that trap heat in the Earth’s atmosphere, leading to global warming. Extreme rainfall events are described as periods of intense rain between one and five days.

The influence of these gases on heavy rainfall events was more pronounced in south and central India. These regions are also likely to witness a rise in the frequency of precipitation extremes by mid or end of the 21st century. This means that extreme rainfall events will take place once every two years in the south and central India compared to the current frequency of over 30 years.

The study has implications for infrastructure, agriculture and water resources, is important because India has seen a rise in extreme rainfall events over the last decade: the July 2005 deluge in Mumbai that claimed more than 1,000 lives; floods in Uttarakhand in 2013 killing around 6,000 people; and the more recent floods in Tamil Nadu (2015) and Bangalore (2016).

“In general, warmer climate due to anthropogenic forcing increases the moisture holding capacity of the atmosphere. Increased moisture in the atmosphere results in more intense extreme rainfall events,” said Vimal Mishra, associate professor, civil engineering department at IITGn, and lead author.

Previous studies have looked at trends over rainfall extremes, but did not quantify the contribution of man-made emissions.

The new study by a four-member team used two data sets — from detection and attribution projects and CMIP5 — to quantify the role of anthropogenic warming on extreme rainfall over India.

Most research till now has focused on the role of surface air temperature during extreme rainfall events to find a negative relationship. The study used Dew Point Temperature (DPT) — temperature at which saturation of water vapour takes place — as it is considered as a better predictor of precipitation extremes. It found an increase in extreme precipitation events and dew point temperature.

As maximum rainfall increased in the range of 5%-15% between 1979 and 2015 in western, central and peninsular India, so did dew point temperature by 0.25-0.50 degrees Celsius during the same period.

“Since surface air temperature is affected by rainfall during the monsoon, it does not provide a robust relationship between rainfall extremes and temperature over the tropics,” said Mishra.

Annual maximum precipitation (AMP), however, did not increase over some regions, including the Gangetic Plain, north-eastern India and Jammu and Kashmir.

“The decline in AMP in the Gangetic Plain region can be attributed to a significant reduction in the monsoon rainfall driven by the increased atmospheric aerosols and warming of the Indian Ocean,” stated the study.

The study titled ‘Increase in Extreme Precipitation Events under Anthropogenic Warming in India’ was published in Weather and Climate Extremes, an international peer-reviewed journal, on March 22.

First Published: Mar 29, 2018 09:43 IST