A water body has always been a prerequisite for settlements and civilisation. We trace the origins of most historic towns and cities to the bank of a river or a sea. Disasters like floods and hurricanes, which could destroy homes and villages in minutes, posed major threats. Yet, no one ever imagined getting submerged step-by-step until there is nothing left of the flourishing neighbourhood. Cities around the world are facing such a threat in recent times. They are going underwater – some are quicker than others, and climate change is not the only reason for sinking cities.
Sinking Cities face the danger of disappearing as they continue to descend underwater. Global warming and melting glaciers are upfront triggers for some. Others are sinking mainly because of man-created issues rotating around urbanisation and human demands, altering the underground components, and causing the land to subside. The events happening simultaneously worsen the impact. Over 1,50,000 people residing in four thousand coastal-large cities are vulnerable to changing water and ground levels as of 2018. Including the numerous smaller coastal communities inflates the number of affected people. In an estimate by the World Bank and OECD, the global flood damage in large coastal cities could cost USD 1 trillion a year when adding the risks from sea-level rise and sinking land.
Sinking Cities – a phenomenon more than climate change
Cities around the globe are plummeting for varying reasons. The rising temperatures and ocean levels, cumulative pressure on the soil affecting its composition, and land subsidence due to mining activities or natural tectonic adjustments are significant reasons. The latter two may result in earth fissures and damaged foundations that make the cities more prone to disasters such as earthquakes and floods.
Land subsidence can happen because of the continuous mining of natural resources like water, oil, gas, etc. However, in recent times, the subsidence due to groundwater extraction has been a prominent topic of concern for most cities around the world. We can understand the process as – the drop of soil from ground level to fill the hollowness beneath it. Imagine the ground below the solid land filled with soil as the first layer and water underneath it. When the water is extracted continuously from the bottom layers, it creates a hollowness under the ground. It takes away the foundational support. As a result, the soil descends one level to find a stable base. As it does that, it carries the land surface along with it and causes the built structures exactly on top to go a few units lower than the surrounding ground. On extraction of more water, the process gets repeated as the soil continues to descend to fill the hollowness, and the city follows. Over several years, the city surface goes way below the ground level, causing the infrastructure, water supply, and related utilities to be disrupted.
As the population continues to grow and urbanisation always thrives, paying no attention to the declining grade of the surface, our cities will eventually sink. Jakarta, Indonesia, is an example of extensive groundwater extraction leading to the city’s rapid sinking (40% of the city is currently underwater). Bangkok, Thailand, which is sinking for the sheer weight of infrastructure and skyscrapers, closely follows. Dhaka, Bangladesh, is dropping because of the mixed effects of groundwater withdrawal and surging water levels in the Bay of Bengal. The city of Manila, Philippines, is also declining at a rate four times that of the rising sea levels. Sea levels in Miami are expected to rise between 13-34 inches by 2040.
Simultaneously, London is miserably trapped in the aftereffects of the last ice age 11,000 years ago. The glacial-isostatic adjustment demands the Thames Barrier be used six times a year– which is twice the original estimation. The same is causing the city to sink at a rate of 2 millimetres a year–it may get to 2 meters by 2200. The city of New Orleans, the United States, is a perfect example of sinking because of human errors while sprawling the city limits. It is projected to suffer from a sea-level rise of 14.5 inches by 2040.
Further, several non-coastal cities, well above ground level, are also suffering from the impacts of groundwater extraction and subsidence. Examples include Delhi, India; Sao Paulo, Brazil; Las Vegas; and Riyadh, Saudi Arabia, followed by many more. The increased natural calamities and required response plan are likely to increase substantial monetary and societal losses. An estimated cost to China was 1.5 billion dollars, and that in the Netherlands was 3.5 billion dollars a year. There have been several suggestions and plans to reduce the dependence on groundwater.
Why will our cities continue to sink?
It is challenging to change people’s preferences. People worldwide have depended on groundwater as the primary source of drinking water because of its abundant availability and lower costs. Piped water systems are costly and have specific limits on the quantity and time of access. Moreover, even piped water systems in some areas use extracted groundwater to distribute. On top of that, the never-ending reliance on mining for other resources is not something that can change overnight.
Countries need to invest funds in righteous ways, along with proper policy and regulations. We have long passed the right time to change things. It is already too late to start, and if we keep on delaying it further, there is no saving our cities from going underwater. The following graph shows sinking cities on different continents.
The graph represents People affected as a result of Sinking Cities across different continents. Image Source: interactive.guim.co.uk/uploader/embed/2017/10/archive-3
As cities continue to grow, we need to accommodate more people in denser communities with taller buildings. The consequences are the increased drinking water demand and continued mining for minerals and other resources from the ground. It is crucial to reconsider the course of development that cities need to stay above the ground level. A report by IPCC on the Ocean and Cryosphere in a Changing Climate verifies that poor development choices affect cities’ weather resistance and capabilities to tackle disasters. A study by USGS on Estimated Use of Water in the United States in 2010 discovered that groundwater extracted for agriculture and irrigation in the USA accounted for 225 million cubic meters per day.
Another study pointed out that four out of five people affected live in Asia. 54% of the Asian population lives in low-lying coastal areas. A few ideas could prevent the sinking for those cities experiencing it at a slower rate. Stopping the groundwater extraction and finding an alternate source for drinking water is one such approach that could make a great deal of difference. Countries like Singapore and Japan took action to tackle the issue before it is too late; others accepted their fate and started preparing for mass evacuation and rehabilitation, as seen in Jakarta, Indonesia. The city is sinking at a rate of 9.8 inches a year. It is the fastest-sinking city globally, and the residents are to be moved to higher lands in the absence of a recovery plan.
Can sinking cities buy more time?
Several cities have tried different innovative approaches. Bangkok designed an 11-acre plant to drain water, while also making groundwater more expensive than piped water. Tokyo introduced groundwater extraction limits and constructed reservoirs in the mountains. Shanghai limited pumping and started recharging their aquifers. Other examples from across the world include – Virginia, where they treat the wastewater, give it the same profile as groundwater- including salinity, and recharge the aquifers for future use. Rotterdam converted a car park into an emergency reservoir; Venice shifted to light material for reducing the weight of buildings. Nye, a town in Denmark, treats collected rainwater and supplies it as the secondary water source for other water-based activities. These methods include considerable investment, though undoubtedly remarkable in the long term. Shifting the city residents to a new place could be even more expensive and gruesome – people in the lowest strata will have to start from scratch with no existing business and properties.
It is crucial to consider the most vulnerable sections in the worst-case scenarios and develop a working strategy to help them where they are likely to lose their occupation and earnings against disasters or cities’ sinking. The best way forward is to prepare for Coastal Hazard Strategy, a Disaster response strategy for increased calamities, adapting to the alternative sources of drinking water, and limiting development weight on the ground. The hope lies in reducing social conflict, developing local political adaptation plans, and fighting climate change by innovating and investing in socioeconomic benefits through climate -development.