Supercyclones and Extreme Floods: A Not So Bright Future

Exposure to flooding from cyclone storm surges, such as those brought on by cyclones the size of supercyclone Amphan, is “extremely likely to increase” in the future in South Asia if greenhouse gas emissions continue at the same scale, warns a study.

The research was led by the University of Bristol and included scientists from Bangladesh. They looked at how the population exposure to a storm surge of Amphan’s scale changes in future emission scenarios. Super cyclone Amphan, the costliest cyclone in the northern Indian Ocean, struck India and Bangladesh in 2020, heavily impacting lives and infrastructure and displacing millions.

Intense cyclones like Amphan would likely expose more than two and half times the population in India (250%) to storm surge flooding of more than one metre by 2100, compared to the event in 2020, in both business-as-usual and high-emissions scenarios. Bangladesh, meanwhile, showed an increase in exposure of more than 80% of the population to low-level flooding (above 0.1 m) in both scenarios.

A “strong, rapid and sustained greenhouse gas reduction” is essential to achieve the goals of the Paris Agreement and to reduce losses and damages of highly vulnerable countries like Bangladesh and India, says study co-author AKM Saiful Islam at the Bangladesh University of Engineering and Technology (BUET). Loss and damage may occur when the consequences of climate change overwhelm adaptation limits and where adaptation has not been optimally implemented.

“The Loss and Damage mechanism in the [UN climate negotiations] is extremely important as increased population exposure in future cyclones will cause more losses and damages in the coastal regions of Bangladesh and India,” Islam told Mongabay-India.

Observers Mongabay-India spoke to point out the lack of progress on loss and damage commitments after developing countries pushed concerns about growing climate-induced loss and damage in the UN climate negotiations (COP26) in Glasgow in 2021.

Rethinking climate adaptation plans

“Tropical cyclones have been impacting the Bay of Bengal almost every year for the last 6 years, hitting Bangladesh and India. Although Bangladesh is a role model for managing disasters and human fatalities, the losses and damages from recurrent cyclones are accumulating and beyond our adaptation limits,” added Islam. “We need new strategies and funding to cope with changing risks induced by climate change.” The latest IPCC report states with high confidence that tropical cyclones with higher intense categories will be more frequent in the future.

In India, advancing sea levels is devouring several coastal hamlets in cyclone-prone Odisha’s Satabhaya forcing communities to relocate permanently. In Bangladesh, the water level at Dalia point (barrage) on the Teesta river exceeded all historical records on October 20, 2021. “The extremely high record water level during this month after the monsoon season is very unusual. The flood bypass was broken, which saved the barrage,” notes Islam on loss and damage.

In the light of the recent and previous relevant research that has sounded warning about future climate change impacts, authors call for India and Bangladesh to revisit their national policies and adaptation strategies for tackling climate change. “This study has clearly shown that more coastal populations will be exposed in the future to stronger cyclones and sea level rise under global warming. Coastal afforestation and many other nature-based solutions would help to increase our resilience as they provide essential benefits and services to people,” according to Islam.

Using sophisticated climate models from CMIP6, the researchers modelled future sea-level rise according to different future emissions scenarios: a low emission scenario (SSP1-RCP2.6), a business-as-usual scenario (SSP2-RCP4.5), and a high emission scenario (SSP5-RCP8.5).

They also estimated future populations across India and Bangladesh to anticipate how many more people storm surges could affect by 2100. The study considered different severity levels of flood depth: low (>0.1 m), medium (>1 m), and high (>3 m) flooding.

“Storm surge causes the largest loss of life during super cyclones, so it was important to focus on this aspect. The more aspects of these cyclones we include, the less certain we can be about the overall climate change signal, so it’s important to start with just one thing,” said lead author Dann Mitchell, Professor of Climate Science at the university’s Cabot Institute for the Environment.

“Low-lying areas such as the coast of Bangladesh and India will certainly see negative impacts of climate change, so every 0.1degree Celsius limit in temperatures will help their populations,” Mitchell told Mongabay-India.

For the lowest emission scenario consistent with the Paris Agreement goal of keeping global average temperatures increase well below two degrees Celsius above pre-industrial levels, an intense cyclone would expose still a substantial percentage of people (50-90%) in India; this population exposure goes up to 250% in case of extreme storm surge flooding (flood depths of more than three metres) in a high emission scenario.

In Bangladesh, the researchers found a 0-20% exposure increase for the lowest emission scenario and a 60-70% increase for the high emission scenario. The difference in exposure between the two South Asian countries is because more people in Bangladesh are projected to move inland to cities from coastal areas, added Mitchell. Most of this change in exposure for both countries comes from increased sea level rise rather than changes in population densities.

Commending the study, Indian environmental economist Saudamini Das, who is not associated with the research, says, despite the storm surge flooding exposure difference between India and Bangladesh based on the 2020 baseline, there is no time to be complacent. “If the baseline changes, then the comparative differences in impacts between India and Bangladesh will change,” Das told Mongabay-India, pointing out that if we factor in grassroots efforts and recent migration trends due to COVID-19, then the future impacts may also change. “In the pandemic, we saw mass reverse migration from urban to coastal areas; state governments also supported the returnees with rural jobs schemes. So the migration trends may also differ in the future, and the population exposure will also differ.”

“While India and Bangladesh have made progress on disaster management, we still have a long way to go as impacts from extreme weather events accumulate,” notes Das.

Indian oceanographer Sugata Hazra, who was not associated with the study, adds that in the absence of bathymetric data of delta rivers, surge heights are overestimated.

Event attribution in loss and damage

Odisha-based environmental activist Ranjan Panda adds that the dearth of scientific evidence that disentangles the role of human-induced climate change in an individual event from other drivers of the event in developing countries such as India has impeded efforts to address loss and damage.

For example, in a recent paper, extreme weather impacts of climate change: an attribution perspective, researchers warned that while attribution science has led to major advances in linking the impacts of extreme weather and human-induced climate change, “large gaps in the published research still conceal” the full extent of climate change damage.

The paper underscores that attribution studies on individual events are “currently lacking” for a number of regions and hazards, including key flood events in South Asia, among other regions. Further, basins with some of the most devastating storms of the past, such as Cyclone Nargis in the Bay of Bengal, “remain understudied.”

“We really don’t have a comprehensive overview or detailed inventory of what impacts climate change is having today, yet,” says Friederike Otto from the Grantham Institute – Climate Change and the Environment at Imperial College London, co-author of the climate change attribution study, in a media release. But we do now have the tools and advanced understanding to create such an inventory, but these need to be applied more evenly across the world to improve our understanding in areas where evidence is lacking. “Otherwise, we are denying countries the knowledge to make the best use of sparse funds and improve chances for people to live safely and adapt to the changing climate,” she concludes.

Panda further argues that discussions on loss and damage must also embrace issues of cultural identity, loss of livelihood-linked skills, mental health due to climate change and right to common property resources.

“Resettling displaced communities permanently in other locations and expecting them to fend for themselves is not the answer. We need to back them up with policies that are gender inclusive and factor in rights. In Odisha, we advocate that the state government push the central government to put pressure on the global community to access climate finance, instead of relying on central funds to help populations deal with climate risks,” added Panda.

“Currently the central and state governments do not have sufficient funds to deal with the challenges that climate change-induced loss and damage pose to the communities and local governments,” adds Panda.

Climate change and populations are intrinsically linked. Roman Hoffman, who studies climate migration, says it is important to have both angles covered when we try to understand what the world will look like in the future and how vulnerable our communities will be to these changes.

“On one side, populations been the one main driver of global emissions driving climate change and also affecting the environment. So that would be one important area where populations come into play. But then, of course, also at the same time, populations in their well-being and health, livelihoods are the ones primarily affected by climate change and its impact,” Hoffman, a postdoctoral researcher at the Vienna Institute of Demography and the Potsdam Institute for Climate Impact Research, told Mongabay-India.

“So aside from the exposure of populations to impacts of climate change, what also matters is the vulnerability of these populations,” Hoffman said.

In areas where more people live and where more buildings and more assets are located, their losses and damages tend to be more severe and more significant because a large number of people are affected. “In South Asia, in Bangladesh and India, we have infrastructure, we have today a large population, and we still have a positive population growth for all the countries in South Asia, although the population growth has declined substantively in the past decades; so exposure plays an important role here,” added Hoffman.

Making important decisions today will be crucial for mitigating future climate change impacts. “And of course, now with the greenhouse gases that have already been admitted, we know that climate change is already happening, and we can see that in our surroundings, and it will continue to happen. So we have already caused the damage. We also need to think about how we can improve in terms of adaptation and protection of populations. And here it is important to focus on the most vulnerable people in India and Bangladesh,” added Hoffman.

This story was first published in Mongabay India