Sinking cities, rising seas: an op-ed by Christian Aid

Published by Flemmich Webb on

By Dr Kat Kramer, Christian Aid’s Global Climate Lead

To coincide with the launch of the Intergovernmental Panel on Climate Change’s (IPCC) Special Report on limiting global warming to 1.5ºC above preindustrial levels earlier in October, Christian Aid launched its own report, “Sinking Cities, Rising Seas”. In this, we surveyed eight cities from around the world and highlighted that their respective vulnerabilities to sea level rise were not just a function of the changing climate, but also because of the development paths that each has followed.

The IPCC’s report noted that even with the current atmospheric loading of greenhouse gases, “warming …will persist for centuries to millennia and will continue to cause further long-term changes in the climate system, such as sea level rise, with associated impacts…”. Even if the miracle occurred that all human-derived emissions dropped to zero permanently today, sea level rise will remain an issue that needs to be addressed as cities develop.

The IPCC report predicts that sea level rise by the year 2100 is for an average of 40cm if warming is limited to 1.5ºC and 50cm if 2ºC is reached. This is considerable when some cities, like Jakarta and Houston, have areas that are below current sea level. Bangkok averages only 1.5m above current sea level.

It is not sea level rise on its own that is the concern, however, but this coupled with other climatic impacts, including increasing storm strengths and the naturally occurring storm surges, posing flood risks to low-lying cities.

According to Coastal Wiki , sixty-five percent of cities with populations above 2.5 million are located along the world coasts. Rising sea levels and the potential for accompanying enhanced storm surges have a potential to impact large numbers of people.

The eight cities in the Christian Aid report, include some of the world’s most populous, including Shanghai, Dhaka, Lagos and Manila, each of which commands a spot in the global top twenty. These, and the other four cities discussed, are not only coastal and low lying, but are actively sinking. Climate change is acting as a risk multiplier on top of vulnerabilities from poor development decisions that are causing the sinking.

Jakarta is reportedly the fastest sinking city in the world, at a rate of around 25.4cm per year, resulting from its large quantity of groundwater extraction. Over half of its 10.3 million people lack access to piped water, and the surface water is heavily polluted, so illegal wells are common and cumulatively lead to subsidence. The pattern of development has been such as to leave the city without natural sponges: 97% of the city is covered in impermeable asphalt and concrete, and the rivers are unable replenish the soils with new sediment. Natural flood buffers, such as mangroves have been chopped down to make way for shanty towns and apartment buildings, further reducing the city’s resilience to floods. The sheer weight of the buildings is also a problem causing further sinking: sometimes the rivers flow upstream because the land is being so deformed.

The weight of buildings is also a problem in Bangkok and Shanghai. Thailand’s National Reform Council notes that there are around 700 buildings of over 20 storeys and 4000 of between 8-20 floors in Bangkok. This places a large amount of pressure on the land where they sit.

Like Jakarta, ground water extraction and resulting subsidence is also an issue in Bangkok, Lagos, Manila, Dhaka and Shanghai. In Manila, upstream rice irrigation and the building of fishponds in tidal channels are also at fault, and even stop the flow of water from wells. Unregulated use of water for golf courses and swimming pools of the affluent also impact on the ability of others to access drinking water.

Despite being pincered between the twin vulnerabilities of sinking cities and rising seas, some of other the cities we surveyed have taken active measures to reduce their vulnerability. Bangkok enacted a Ground Water Act in 1977, which regulates groundwater extraction and brought in charges for water in 1985 so that only 10% of water is now taken from aquifers, helping to reduce sinking. Bangkok and Shanghai are both actively rehydrating their underlying geology by pumping water back into the sediments. Dhaka has established an early warning system and storm shelters to help protect its people.

In contrast, a development decision to build a sea wall around a new 10km2 financial district in Lagos built on in-filled land may push the storm surges and rising seas towards neighbouring islands and the rest of Lagos. Such unsustainable development may not end well for the city and its people.

Perhaps the greatest irony can be found in Houston. The city is low lying and like other cities is sinking through groundwater extraction. What makes Houston’s situation exquisitely ironic in the context of seas rising because of climate change, is that the city is also sinking because of extraction of oil and gas, the burning of which causes climate change. The oil and gas industry have effectively staged a two-pronged attack on the city’s resilience.

The Lloyds City Risk Index rightly emphasises the need for resilience building. But while insurance is helpful after an event through claims payments that help nations, businesses and communities get back on their feet post disaster, it also helps build resilience by working with those affected to reduce risks. Efforts are now being focused by the insurance sector and organisations such as the United Nations on helping improve access to insurance products and services, especially in emerging economies. These need to be implemented in ways that strengthen other risk management activities, such as early warning systems and climate change adaptation, that deliver higher benefit-cost ratios for the most vulnerable.

Sea level rise is an issue that we need to consider carefully for both the near and long term, in ensuring cities around the world are resilient to the changing climate. It should also serve as a spur to reduce global greenhouse emissions: radically and rapidly, not just to reduce the risk of GDP losses, but, vitally, to reduce the threat faced by tens of millions of people