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Rising Sea Levels Threaten to Flood Lakshadweep: Study – The Wire Science



An aerial view of one of the Lakshadweep islands. Photo: Anuj Chauhan/Unsplash

Lakshadweep resident and researcher R.M. Hidayathulla, who drew attention to the disappearance of a small, uninhabited atoll island in the archipelago in the Arabian Sea in 2017, has closely witnessed the land contract from erosion from a combination of factors; rising sea levels will likely worsen it. “My house is near the sea and coastal erosion is increasing day by day; we do want development but it should be scientific and sustainable,” Hidayathulla lets Mongabay-India know amid the simmering controversy surrounding the coral-fortressed archipelago, an environmentally fragile melting pot of cultures, roughly 200 kilometres off the west coast of southern India.

Hidayathulla works in the agriculture sector in Kavaratti, the capital of Lakshadweep, India’s smallest Union Territory, with islands barely a few metres above sea level. Although the smallest of the major oceans on Earth, the Indian Ocean, including the Bay of Bengal and the Arabian Sea, is the fastest-warming tropical ocean. The Lakshadweep islands consist of coral formations built upon the Laccadive-Chagos submarine ridge “rising steeply from a depth of about 1500 m to 4000 m” off the west coast of India. This ecoregion consists of the Maldives, the world’s most low-lying terrain and the Chagos archipelago, a British Indian Ocean territory.

“We have concrete structures surrounding our islands for protection but what we need are natural protections (nature-based solutions) like mangroves,” Hidayathulla points out, referring to the Lakshadweep archipelago of 36 islands with an area of 32 sq km comprising of 12 atolls, three reefs, five submerged banks and ten inhabited islands. With a population of 64,000 people and 2000 people per square km, it’s one of the most densely populated parts of rural India.

According to Prasad K. Bhaskaran, an expert on wave ocean dynamics, even with a low greenhouse gas concentration scenario (technically called the representative concentration pathway 2.6), sea levels around Lakshadweep, are expected to rise to levels “dangerously close” to the global projections by the end of the century, roughly over the next two generations.

“Our projections based on best performing models show that sea levels can rise by 0.78 metres by the end of the century. Although the maximum sea surface height values (0.78 metres) is less than the global sea-level rise projected by the Intergovernmental Panel on Climate Change (IPCC) (0.8–2.0 m) by the end of the century, it does not imply that the islands are safe from rising sea levels,” emphasised Bhaskaran based at the Department of Ocean Engineering and Naval Architecture, IIT Kharagpur, quoting the latest paper, of which he is a co-author.

The trend in sea-level rise for the Arabian Sea for 1973-2010 is about 1.72 mm/year, while for Lakshadweep Islands the tide gauge data during 1981-2005 indicates a sea-level rise of 0.5 mm/year. The sea level rising trend within the Lakshadweep archipelago, which has a lagoon extent of 4200 square km, is projected to be lower than that of the Arabian Sea basin by the end of the century, adds Bhaskaran, who co-authored the study with Athira Krishnan, Saikat Kumar Paul and Aysha Jennath.

This difference, they said, is due to the density variations in the seawater, ocean heat and its transport, and ocean circulation features. All the islands show different levels of flooding in future sea-level rise scenarios and their susceptibility to flooding also differed.

The smaller islands of Chetlat and Amini will likely see land loss from sea-level rise along most of their shorelines; the land would come under the sea when the sea level becomes higher than the elevation of the land. But the larger islands Kavaratti and Minicoy were also shown to be vulnerable to the impacts of future sea-level rise: rising waters of the Arabian Sea may chip away the land along 60% of these larger islands’ shorelines, as the projections show. Androth Island was observed to have the least inundation under all climate change scenarios.

“The projected inundation can be problematic for the islanders as the residential areas are quite close to the present coastline. The only airport in the archipelago is located at the southernmost tip of Agatti Island and there is a high likelihood of damage due to inundation in this region. Since the base map considered for this study is from the year 2000, much of the predicted damage might have already occurred,” adds study co-author Aysha Jennath, research scholar, Department of Architecture and Regional Planning, at IIT Kharagpur.

No stranger to climate change

Sea level rise can enhance the coastal erosion processes and lead to further loss of land. In coastal areas which are easily eroded, higher sea levels can lead to increased inland migration of shorelines as well as expose previously protected areas to damage, and Lakshadweep Islands are “particularly low-lying and the coastal slopes are gentle. So sea-level rise can move inward much higher and cause more damage.”

The reality of development on the islands requires a fine balance in addressing the environmental concerns and the needs of the people on the 1o islands that are inhabited. For example, Coastal Regulation Zone Notification 2011 required part of the coastline extending to 200 meters from the High Tide Line (HTL) be made a ‘No-Development Zone’. “However this (the 200 metres setback) was met with opposition from the islanders. Their concern is valid as there are certain portions of the islands that are less than 100 meters wide. On the other hand, the regulation of industries and tourism is required due to the delicate ecosystem there,” Jennath said. According to the 2018 notification it is now 50 m from the HTL.

Climate change and its impact on the fragile ecosystem is acknowledged on paper by the Lakshadweep administration – it did come out with a climate action plan in 2012, which also reiterated that while erosion takes place due to storm surges, wave attacks and destruction of coral reefs (reef structure buffers shorelines against waves, storms, and floods, helping to prevent loss of life, property damage, and erosion), projected rise in sea level may worsen it.

Usually calmer than the Bay of Bengal, the Arabian Sea is getting more active with the rapid intensification of cyclones due to climate change; cyclone Ockhi and Tauktae were the most recent ones. High energy waves that pound the shores during these events also contribute to eroding the coasts. Additionally, climate change together with human-caused actions has disrupted the status quo of the cyclical process of erosion (shoreline retreat) and accretion (accumulation) so much so that the shorelines are not able to accrete mass at the same pace as they lose, the researchers explained.

The Lakshadweep coral fringes that protect the shoreline from waves and storms are struggling to keep up with the changes that have come thick and fast, like their counterparts elsewhere in the world. Australia’s Great Barrier Reef, a UNESCO-listed World Heritage Site, experienced its most extensive bleaching event to date in 2020. The 2020 event was the third major bleaching event in the last five years for the world’s largest reef system, spanning more than 344,400 square kilometres (133,000 square miles). Previous ones took place in 2016 and 2017, with the 2016 event considered the most severe.

Coral reefs in peril

Lakshadweep has experienced three major bleaching events from 1998, 2010 and 2016 corresponding to the El Niño events of those years. While the reefs recovered from the 1998 event, recovery following the 2010 event was slower. Just when the reefs were showing signs of recovery from the 2010 bleaching, the El Niño hit the reefs in 2016. Cyclones, including Ockhi in 2018, followed this collapse of coral. Coupled with the narrowing of the intervals between the bleaching events, commercial reef fishery in recent years, has undermined the resilience of these ecosystems.

It’s a world of hurt for coral reefs globally with countries falling short of their commitments to meet the Paris Agreement’s goal of limiting global temperature rise by two degree Celsius—ideally 1.5 degree Celsius—by the end of the century. According to the IPCC, coral reefs would decline by 70-90% with global warming of 1.5 degree Celsius, whereas virtually all (> 99%) would be lost with two degree Celsius.

Chris Perry, a professor in tropical coastal geoscience at the University of Exeter, the United Kingdom, explains that sea level is a key influence on how reefs have grown vertically over the past few 1000 years and in most cases reefs have shown an impressive capacity to grow vertically at rates that have broadly kept pace with past sea level rises. “This has happened of course under conditions with limited to no significant direct human influence on reefs and where it would appear that coral communities have generally responded well to episodic storm etc disturbances,” Perry told Mongabay-India.

Perry, whose research seeks to address questions about the response of coral reefs and reef landforms to environmental and climatic change, added that the interaction between future sea-level rise and reef growth is important because the water depth above the reef surface has a strong influence on wave energy transfer across the reefs to island shorelines. “In the near future, one of the concerns for island nations is thus about whether reefs will keep pace with sea-level rise – if not it is reasonable to assume that wave energy levels reaching the shorelines of islands will increase – and this may then lead to increased shoreline erosion or higher rates of shoreline mobility.”

While sea-level rise itself will not have a major impact on coral reef accretion (the change in water depths projected in any studies are not sufficient to drown reefs) but, even modest increases in water depths above reefs may be enough to change wave exposure regimes. “The major concern is that the vertical growth capacity of reefs in most regions, including the Indian Ocean, is being impaired by either direct human impacts on reefs and/or by climate-driven stressors – especially coral bleaching caused by ocean heat stress events.”

Building on to the evidence shown in recent studies that reef growth rates are being impacted, a recent paper in May in Proceedings of the National Academy of Sciences, of which Perry is a co-author, showed that increasing frequency/intensity of bleaching as many models predict will happen over the next few decades (and beyond without rapid action on greenhouse gas emissions) will have a major impact on the capacity of the region’s reefs to respond positively to a rise in sea-level rise.

“It is hard to see this not also being an issue in the Lakshadweep,” Perry said. The international study was initiated at the ARC Centre of Excellence for Coral Reef Studies (Coral CoE), which is headquartered at James Cook University. The key message is “saving coral reefs requires immediate and drastic reductions in global carbon emissions.”

Although it will not “limit the nature of temperature-driven bleaching”, Perry says that local conservation efforts are critical because they will offer scope for the reefs to spring back from the bleaching impacts. “The best chances for rapid recovery and the maintenance of some reef accretion potential after these events will be on those reefs that are the least impacted by, for example, the effects of high fishing pressures, poor water quality etc. Local conservation should thus focus on giving reefs the best chance of recovery as much and as fast as possible from bleaching,” he said.

Aysha Jennath adds that restoring corals lost due to coral bleaching by coral farming, especially by using more heat-resistant strains can help in enhancing the natural protection offered by the corals. Soft engineering solutions, as opposed to hard armouring solutions like sea walls and tetrapods, would be the best option to tackle the erosion. Soft engineering options include beach creating measures like beach nourishment, geotubes/geobags can be used to regain the lost beaches.

“Beach nourishment can be done using the material that is dredged from the navigation channel itself. Geotextile bags to be used to construct specific slope and height tolerances, to protect structures and to provide additional height to existing levee systems when floodwaters reach critical levels.” “Reef balls, which are submerged breakwaters deployed to the ocean floor and anchored, can help inshore stabilisation without affecting other areas. They can also act as a habitat for coral and fish,” she suggested.

This article was first published on Mongabay India and has been republished here under a Creative Commons license. Read the original article.



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