Global warming: NASA tool predicts which city will flood first; Mangalore, Mumbai at risk

Mangalore in Karnataka is at a higher risk of flooding from rising sea levels because of melting glaciers than coastal cities such as Mumbai and New York, data released by Nasa shows.

Over the next 100 years, glacial melt could push up Mangalore sea levels by 15.98cm compared to 15.26cm for Mumbai and 10.65cm for New York, says the study carried in the journal Science Advances. Mumbai and New York are traditionally believed to be the most vulnerable.

The findings are based on a forecasting tool, gradient fingerprint mapping (GFM), developed by the scientists at the US space agency’s Jet Propulsion Laboratory.

It allows planners to see exactly how melting glaciers can push up sea levels for 293 major port cities, including three from India – Mangalore, Mumbai in Maharashtra and Kakinada in Andhra Pradesh.

“This is the first time our method will enable planners and engineers to retrieve data about sea level in their area, and get updated numbers when new data about glacial melting becomes available,” Surendra Adhikari, a co-author of the study, told Hindustan Times on Thursday.

GFM will show how sensitive local sea-level rise is to glacial melt, allowing scientists and planners to identify the ice sheets that pose bigger risk. An ice sheet is a continental glacier that covers a large area.

“As cities and countries attempt to build plans to mitigate flooding, they have to be thinking about 100 years in the future and they want to assess risk in the same way that insurance companies do,” said Erik Ivins, senior scientist at the laboratory.

Almost 75% of the world’s freshwater is stored in glaciers and ice sheets and their melting, because of global warming, is a major contributor to rising seas.

The rise is not uniform across the globe because of gravity, the “push-pull influence” of ice, the wobble of the planet and local factors.

Shrinking ice sheets exercise lower gravitational pull on sea waters, allowing them to flow away. Diminishing ice mass allows the land below to swell, and this change in surface impact the wobble – or rotation — of earth, all of which influence how water is distributed across the planet.

Rising seas erode coasts and can fuel storm surges and flooding. Under the high emissions scenario for greenhouse gases, sea level will rise by 0.51 -1.31m by 2100, according to National Oceanic and Atmospheric Administration.

The Indian subcontinent is likely to lose 14,000 sq km of land if sea level rises by a metre, according to some estimates.

In India, almost 40 million people will be at risk from sea-level rise by 2050, according to a UN report, with people in Mumbai and Kolkata at higher risk.

Vulnerability is not just calculated by sea-level rise but also the life and property at risk, which puts densely populated cities such as Mumbai and Kolkata at a higher risk than smaller coastal towns and villages.

The other major cause of sea-level rise is the thermal expansion of ocean waters. Water expands on heating and there has been a marked rise in average global temperatures of oceans since pre-industrial times.

The Nasa study was published on the penultimate day of the climate-change talks in Bonn, where signatories discussed the implementation of the Paris climate deal.

While not much progress was made on the Paris deal, 20 countries launched a coal phase-out initiative. Led by Canada and Britain, the “Powering Past Coal Alliance” committed to weaning themselves off coal that still produces about 40% of the world’s electricity — a major contributor to global warming caused by greenhouse gas emissions.

(With agency inputs)