Large parts of Mumbai could be prone to coastal flooding by 2050, according to a recently published study (Getty file photo)

The Arabian Sea could begin entering and flooding most of Mumbai at least once every year by the year 2050, according to a new study that paints an alarming picture of what global warming-induced sea level rise could do to the world's biggest coastal cities. According to the study, previous estimates of how many people would be impacted by rising sea levels in the next few decades were too optimistic. In fact, the study estimates that three times more people than what was previously believed would be impacted by rising sea levels in the coming decades.

The study estimates that by 2050, 30 crore people would be living in areas that would be prone to coastal flooding (a situation wherein seawater floods enters and flood large tracts of land). And, the study estimates, by 2100, land currently home to 20 crore people would be permanently below the high tide line, i.e. a standard high tide would easily overrun areas inhabited by the people.

To make these new estimates, the study tried to correct previous models of estimating the current elevation of land. Essentially, the study arrived at truer estimates of how high land across the world currently is vis a vis sea levels (more on this later) and used this to make better predictions of the impact of rising sea levels decades from now.

The study was carried out by a US research institute Climate Central and was recently published in the journal Nature Communications.

THE FINDINGS

The biggest finding of the new study is that the world's vulnerability to sea level rise is worse than what was previously believed. The study estimates that due to rising sea levels, land currently home to 30 crore people would be prone to chronic flooding by 2050 and by 2100, areas now home to 20 crore people would be flooded every time there's a high tide.

The study has also revised estimates of exactly how much areas of coastal cities would be at risk of coastal flooding by 2050. Coastal flooding takes place when sea water enters and inundates large swathes of land.

The photo below shows the areas of Mumbai that could be at risk (shaded in red) to coastal flooding by 2050. As you can see, the areas at risk cover nearly the whole of Mumbai, including the densely populated south and suburban Mumbai.

Parts of Mumbai that could prone to coastal flooding by 2050 (Image: Climate Central | Tap to enlarge)

On the eastern side of India, this image shows what parts of Kolkata and its surroundings could be impacted by coastal flooding by 2050.

Parts of Kolkata and its surrounding areas that could prone to coastal flooding by 2050 (Image: Climate Central | Tap to enlarge)

The other such cities that are likely to be similarly impacted by coastal flooding, according to the study, include Bangkok, Shanghai, Alexandria and Amsterdam, among others.

CONDITIONS APPLY

The study's estimates of the parts of the world that could be severely impacted by coastal flooding come with important riders.

The estimates do not take into account natural or man-made coastal defences that could prevent sea water from entering cities.

The study's authors also warn that the estimates are meant to only identify areas that *could* be at risk. For any risk management, the spots identified in the research must be studied more meticulously to better understand the vulnerabilities.

HOW THE STUDY IS DIFFERENT

The threat to the word's coastal cities from rising sea levels is not new. Alarming headlines warning of some or the other city going underwater appear in the news every few months. So what is new about this study?

Well, this study has tried to correct our understanding of land elevation across the world. Previously models, based on satellite data, were unable to differentiate between actual land elevation and elevation that was a result of elevated structures or factors such as buildings or tree tops.

Put simply, the older models would mistake tree tops or building rooftops as the actual elevation of land at a particular point, resulting in a flawed estimation of the height of land in various parts of the world, especially areas that are densely populated.

So, the researchers behind the new study used neural networks to correct satellite data and arrive at truer estimates of land elevation across the world.

With a better understand of how high land currently is compared to sea levels, the researchers were then able to revise estimates of what sea level rise that has already been previously projected would do to these lands decades from now.