India already recording events IPCC warned of
India has already started witnessing what the Intergovernmental Panel on Climate Change (IPCC) flagged in its “Climate Change 2021: The Physical Science Basis” report on Monday — so-called compound extreme events, including severe cyclonic storms, floods and heatwaves.
In May, extremely severe cyclonic storm Tauktae intensified rapidly and unexpectedly, clocking wind speeds of 180-190kmph gusting to 210kmph, and resulting in intense spells of rain in Mumbai.
It was a combination of two extreme events — over the ocean Tauktae rapidly intensified from a “very severe cyclonic storm” to an “extremely severe cyclonic storm” within a few hours on the morning of May 17 while over land, torrential rains inundated and crippled the country’s financial capital, shutting down even the city’s Chhatrapati Shivaji Maharaj International Airport.
Such compound or cascading extreme events are expected to be more frequent and may have a high impact in coming years, IPCC warned.
Compound extreme events are a combination of multiple drivers or hazards that contribute to societal or environmental risk. Examples are concurrent heatwaves and droughts, compound flooding (a storm surge in combination with extreme rainfall and river flow), compound fire weather conditions (a combination of hot, dry, and windy conditions), or concurrent extremes at different locations.
“The changing climate state is already altering the likelihood of extreme events, such as decadal droughts and extreme sea levels, and will continue to do so under future warming. Compound events and concurrent extremes contribute to increasing probability of low-likelihood, high-impact outcomes and will become more frequent with increasing global warming,” IPCC said in its report.
Based on 14,000 scientific papers studied by 234 experts, the IPCC report said the world will miss its target of keeping global warming to under 1.5 degrees C over pre-industrial levels, and that this will be exceeded in the next two decades, resulting in a higher frequency and intensity of extreme weather events. Attributing the heating almost exclusively to human activity, it also called for immediate action, including a move away from fossil fuels, if the world wants to keep global warming to under 2 degrees C.
A projection by the panel that may be particularly relevant to India is that the compound effects of climate change, land subsidence and human factors may lead to higher flood levels and prolonged inundation in Mekong Delta and other Asian coasts. An increasing sea level compounded by increasing tropical cyclone storms and rainfall intensity may further increase the probability of coastal city flooding.
“These events are already happening. This is basically one extreme event triggering another or two or more extreme events taking place at the same time. The impact of such events is very high. For example, there can be extreme precipitation and extreme flooding at the same time. Or there is extreme heat leading to heat waves which then triggers wildfires that can make management of disasters very complicated. Another example is of tropical cyclones and extreme rainfall happening together. We can expect such multiple or cascading events taking place together more frequently when there is 1.5 degree C warming,” said R Krishnan, executive director, Centre for Climate Change Research at Indian Institute of Tropical Meteorology and one of the authors of the IPCC report.
The report also said that extreme rain and winds can result in infrastructure damage; the compounding of storm surge and rain extremes can cause coastal floods; the combination of drought and heat can lead to tree mortality; and wildfires can increase occurrences of hailstorms and lightning.
Compound storm types comprising co-located cyclone and thunderstorm systems can cause extreme rainfall and extreme winds than individual storm types, IPCC said, adding that studies also show an increasing risk for breadbasket regions to be concurrently affected by climate extremes with increasing global warming, even between 1.5°C and 2°C of global warming.
India’s 7,516- km-long coastline is particularly vulnerable to compound events, the IPCC report said. “It’s very simple, the Indian Ocean is warming at a higher rate compared to the global average. This is often leading to tropical cyclones intensifying very rapidly. Along with that, we have sea level rise in coastal areas. We are also seeing higher storm surge and strong winds. All of this is coming together with extreme rainfall. Extreme rainfall events are rising at the rate of 7% with every 1 degree C of warming. These are compound events and not singular events. We saw a similar pattern for Amphan, Tauktae and Yaas and this will only become more frequent in future,” said Subimal Ghosh, Institute Chair Professor, Department of Civil Engineering, IIT, Mumbai and another author of the IPCC report.
Krishnan said early warning systems have improved significantly since the 1999 Odisha super cyclone but more accuracy is needed in forecasting the intensity of cyclones. “We need widespread awareness of climate change-related disasters and training in climate change, oceanography and meteorology should start very early from high school,” he added.
“Chances of multiple extreme events overlapping to form compound events are high for coastal cities. The strong winds from the cyclones drive huge waves at 5m or high, pushing water onto the coast and flooding the region. This flood is amplified by the rains from the cyclone. Increasing sea level along the coast is taking this flood level up every year. Sometimes a high-tide can aggravate the flood, taking it several kilometers inland. We already saw these kinds of compound events with Cyclone Tauktae and Yaas this year. While the IPCC report discusses these events and we see them happening, we have not quantified them yet,” said Roxy Mathew Koll, climate scientist, IITM, Pune.