Cycles of floods caused by heavy bursts of rainfall and a rise in droughts due to increased evaporation, this is potentially what India’s climate future will look like as the world barrels towards breaching the 1.5 degree Celsius ceiling for global warming by 2040, a UN report has said. Already, India’s financial capital Mumbai is witness to heavy rainfall days unprecedented in decades that last month left the city flooded and also extracted its toll in human lives. Climate experts have called for urgent steps to address the crisis. Here’s what extreme weather — flagged as being the biggest risk from climate change — could mean for India in the years ahead.
How Will Global Warming Bring More Rain?
In the first part of their Sixth Assessment Report released on August 9 — called ‘Climate Change 2021: the Physical Science Basis‘ — experts of the UN-led Intergovernmental Panel on Climate Change (IPCC) have said that while there has been a decreasing pattern observed in rainfall in the Indian Subcontinent, rainfall will actually increase in the long-term.
But the increase in rainfall will not be paced out across the rainy season. Instead, the country may find itself grappling with monsoon extremes that drive up the frequency of short intense rainy days, which could be punctuated by long spells of no rainfall in between.
“The number of rainy days may decrease, but then when heavy rains occur, they will happen in short spells. So, the frequency of heavy rainfall events are expected to increase," said R Krishnan, Executive Director, Centre for Climate Change Research (CCCR), Indian Institute of Tropical Research and one of the co-authors of the report.
The key factor driving the fluctuation in rainfall patterns in South Asia, according to the report, are aerosols, whose increase has been linked to a decline in South and Southeast Asian monsoon rain since the mid-20th century.
However, as Dr Swapna Panickal, one of the authors of the report who is associated with the Indian Institute of Tropical Meteorology, Pune, pointed out, “The Southwest Monsoon has declined over the past few decades because of the increase of aerosols, but once this reduces, we will experience heavy monsoon rainfall".
What Are Aerosols?
Aerosols are fine particles suspended in the atmosphere, which arise “both from human activities involving burning of fossil fuels, biofuels… and from natural sources (such as desert dust, sea spray and volcanic eruptions)".
Aerosol particles may be both solid or liquid and can have both a heating and cooling impact on the climate. “When the sky is clear, aerosols can reflect incoming sunlight back to outer space… This blocks part of the energy that would have reached the surface, thus having a cool effect on the climate," says the US National Oceanic and Atmospheric Administration (NOAA).
But there are absorbing aerosols, too, “black carbon in particular [which] can trap solar energy within the atmosphere… the enhanced atmospheric heating eventually warms up the surface, and counteracts the cooling caused by reflection". In fact, black carbon has been classified as “a major contributor to global climate change, possibly second only to [carbon dioxide] as the main driver of change". It is emitted by the incomplete combustion of fossil fuels and biomass.
US space agency Nasa says that “aerosols also affect other parts of the climate system like rainfall — reducing rain in areas like India and China… and they alter patterns of wind and atmospheric circulation".
“India notes that climate change is impacting the South Asian Monsoons. The report brings out that the monsoon rainfall is expected to intensify in all ranges of the projected scenarios. Intensity and frequency of heavy rainfall events are projected to be on the rise. India notes that the rising temperature will lead to increased frequency and intensity of extreme events, including heat waves and heavy rainfall," the Union Environment Ministry said in response to the IPCC report.
How Will Droughts And Heatwaves Increase?
In its regional outlook for Asia, the IPCC report said that “heat extremes have increased while cold extremes have decreased, and these trends will continue over the coming decades", adding that marine heatwaves “will continue to increase".
Specifically, in South Asia, “heatwaves and humid heat stress will bemore intense and frequent during the 21st
century", the report said. Experts pointed out that there is also the scenario where droughts become more frequent due to the soil losing moisture at greater rates due to increased temperatures. Due to an increase in temperature, there will be more water evaporation, which will in turn decrease soil moisture and lead to droughts, CCCR’s Krishnan is said to have pointed out.
Earlier this year, reports had pointed to research by the Indian Institute of Technology (IIT), Gandhinagar, which said that climate change would expand the frequency of flash droughts in India, which were described as events that can affect a large region over a two-three week span.
“As air temperature is projected to get warmer significantly in the future due to climate change, monsoon breaks and increased air temperature can exacerbate the flash drought occurrence in India," Vimal Mishra, one of the authors of the study, was quoted as telling news agency PTI.
Why Experts Have Flagged Impact On Cities?
The UN has termed urbanisation a “demographic mega-trend" and close to seven out of every 10 people on this planet will be living in urban areas by 2050. India has also seen a push towards urbanisation and a third of the country’s population now lives in cities and towns. A report by TERI says that “India’s urban population is expected to grow from 410 million in 2014 to 814 million by 2050".
But urbanisation comes with its own unique set of climate challenges, the IPCC report has pointed out.
“Cities intensify human-induced warming locally, and further urbanisation together with more frequent hot extremes will increase the severity of heatwaves, the report said. “Urbanisation is going to intensify heat extremes. It can also lead to heavy precipitation and flooding. The run-off and flooding will increase," Krishnan said.
So, apart from warming, the massively built-up urban landscapes may also witness more flooding. “Urbanisation also increases mean and heavy precipitation over and/or downwind of cities and resulting run-off intensity," IPCC said.
It especially underscored the threat to coastal cities, where “the combination of more frequent extreme sea level
events (due to sea level rise and storm surge) and extreme rainfall/riverflow events will make flooding more
probable". That should be a major worry for India given the estimated 3.7mm annual rise in sea levels in the Indian Ocean and a more than 7,500-km long coastline that is studded with several large coastal cities like Mumbai, Kolkata, Chennai, Surat, etc.
What Has To Be Done?
Insisting that “it is unequivocal that human influence has warmed the atmosphere, ocean and land", IPCC said that the urgent need is to limit “human-induced global warming to a specific level" which would require “limiting cumulative carbon dioxide emissions, reaching at least net zero CO2 emissions, along with strong reductions in other greenhouse gas emissions".
“Scenarios with low or very low greenhouse gas (GHG) emissions lead within years to discernible effects on greenhouse gas and aerosol concentrations, and air quality, relative to high and very high GHG emissions scenarios," it said, adding that “discernible differences in trends of global surface temperature would begin to emerge… within around 20 years".
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