The frenzied pace of life is putting great pressure on cities. While on the one hand climate change impacts present significant risks, humans attempting to meet their often unsustainable demands from nature are adding to the perils. These have reached a stage where cities’ very existence is threatened
‘New York City is sinking at the average rate of 1 to 2 millimeters per year’. ‘Airport built on water in Japan is sinking into sea’. Such news reports and comments are drawing the attention of policymakers, businesses, and civil society across the globe. While to some extent these occurrences are due to geological reasons, the big contributor is anthropogenic or human activity. Therefore it is unfortunate that the common man is not much concerned or even fully aware of the trend and its consequences.
The trend of sinking cities is not limited to some cities, regions, or continents, but is rather widespread. Jakarta, Lagos, Houston and Venice are among other cities mentioned by a World Economic Forum report, which are impacted significantly and are in danger of disappearing completely by the end of this century. As can be seen, they stretch across every continent – Asia, Africa, the Americas, and Europe.
Closer home, in India, the situation is equally grim if not downright scary. A July 2023 Times of India report quoted a study by New Jersey based Climate Central which warned that several parts of Kerala were in much danger from the effects of sea-level rise. The projected sea level rise shows that parts of four districts Ernakulam, Kottayam, Alappuzha, and Thrissur could be below sea level by 2050. The same report states that many parts of interior Kerala could also be in danger from sea level rise.
What causes sinking cities?
One obvious factor causing cities to sink is the rising sea levels. This is turn is caused by the melting of glaciers in the polar regions pouring huge amounts of water into the oceans. Currently, about 10% of land area on Earth is covered with glacial ice. Almost 90% is in Antarctica, while the remaining 10% is in the Greenland ice cap. The WWF website explains what are glaciers and sea ice saying that Sea ice forms and melts strictly in the ocean whereas glaciers are formed on land. Icebergs are chunks of glacial ice that break off glaciers and fall into the ocean. While glaciers (ice from land) melt, they run off into the ocean and raise the level of the ocean. Sea ice, on the other hand, is often compared to ice cubes in a glass of water: when it melts, it does not directly change the level of water in the glass. Instead, depleting Arctic sea ice triggers a host of other devastating consequences….These could range from impacting the living creatures there like polar bears and walrus while also altering climate patterns. It is interesting to note here that huge sheets of ice on the ocean and on land act as mirrors reflecting the excess heat from the sun back into space thereby keeping earth cooler. Therefore while glaciers and sea ice melt due to rising temperatures, the sheets of ice (mirrors) reduce and so does the heat reflecting ability. This exacerbates warming.
Global warming which is an outcome of greenhouse gas emissions caused by human activity on Earth is one major reason for sea-level rise which is posing grave risks to the very existence of coastal cities. Another reason which should be very evident to even the layman is the over extraction of earth’s resources, mainly water. Several publications reported some years ago that Beijing was sinking almost 6 cms every year – due to over extraction of groundwater. As we humans dig into the earth and extract resources from oil to water to minerals at a frantic pace to meet our almost insatiable demands, we leave gaping holes beneath the earth’s surface and little support for the massive infrastructure that we have built overground during the last many decades. Rapid, relentless, and accelerating urbanisation adds to this danger continuously. This phenomenon known as land subsidence can of course happen inland too, not just along the coast.
What are cities doing about it?
The first imperative is of course to understand, measure, record, and monitor the extent of land subsidence. Some of the developed world countries, notably Tokyo have been able to do it. On the other hand many developing world cities, as in Asia, may not have the knowledge, skill, or financial resources to undertake these often complex and expensive geological and hydrogeological studies to measure, monitor, and combat land subsidence.
Among the measures to combat sinking, one obvious action is to take some pressure off these vulnerable cities. Indonesia, for example, is considering moving its capital from Jakarta, one of the fastest sinking cities of the world to a different location, possibly to Nusantara. This could relocate large masses of the population as well as economic activity away from Jakarta and ease some of its burden. In order to control land subsidence, city managements must put in place strict regulations with respect to extraction of ground water. Tokyo has been able to do this effectively thereby controlling land subsidence. In India, while many states and cities do have strict legislation to prevent over extraction of ground water, implementation has been less than satisfactory. In any case given the capacity shortfall for supply of fresh water to citizens, restricting borewells will leave the residents with no options. Shanghai has been undertaking active recharge of ground water in order to control land subsidence. The city pumps in water into the subsurface to compensate for the water drawn out. But the principle seems on shaky ground given that in the first place, water is extracted to meet water needs so where is the water available to pump into the earth. Unless, of course this active recharge is undertaken during heavy rainfall or flooding time when there is an excess of water.
Man-made shore-based sea walls, dikes and similar structures can prevent or limit the erosion of land from the shore and thereby reduce the vulnerability of cities. However, such interventions come at a huge cost and the benefits accruing from such costs may be tenuous. Additionally, such structures could affect the natural sea-beach-shore ecology and habitats which may strip the coast of natural defense mechanisms in times of floods, storms, tsunamis, etc. Then there are soft or natural options such as beach nourishment or replenishment and plantation of mangroves and other coastline vegetation. That said, the efficacy of sea walls has been experienced in many instances. In India, during the 2004 tsunami triggered by a massive Indian Ocean earthquake, Pondicherry remained relatively unscathed primarily due to the 300 year old stone seawall. Alongside, after the tsunami, India started planting coconut tree saplings along the coast. Studies have proved that these could significantly tame a future tsunami and reduce wave heights.
As we have seen, among the various outcomes of rapid urbanisation, several present significant challenges. Sinking cities is among the most onerous where infrastructure assets worth trillions of dollars may be destroyed altogether. In the meanwhile, these could be seriously threatened by storms, floods, hurricanes, and tsunami events. It is necessary that cities undertake intensive citizen outreach programmes and build awareness to usher in a more sustainable lifestyle – be it waste management, green mobility or water conservation. Our march towards a circular economy must be the primary marker of this transformative journey. Else we will have no option but to build floating cities or live our entire lives on ships and boats.
As human dig into the earth and extract resources, we leave gaping holes beneath the earth’s surface and little support for the massive infrastructure