From Jakarta to New York: How to save sinking cities - What in the World podcast, BBC World Service

Key Concepts

Sinking cities, groundwater extraction, climate change, sea level rise, thermal expansion, land sinking, sponge cities, nature-based solutions, urbanization, sustainable urban development, groundwater recharge.

Jakarta: A Case Study of a Sinking City

Jakarta, Indonesia, is one of the fastest-sinking cities in the world due to both natural and man-made factors. Natural factors include its location on a low-lying delta with compressible soil, making it prone to compaction. The primary man-made factor is the excessive extraction of groundwater. This extraction causes the soil surface to sink, leading to the sinking of the ground on which buildings are built. The northern part of Jakarta has sunk by as much as 11cm per year between 2014 and 2020. Many residents in northern Jakarta have had to elevate their house floors, sometimes up to one meter over ten years, to cope with frequent flooding. Uneven land sinking has caused some buildings to lean.

Climate Change and Sea Level Rise

Climate change contributes significantly to the problem of sinking cities through sea level rise. Georgina Rannard, a BBC climate reporter, explains that sea level rise is primarily driven by two factors: melting glaciers and ice sheets, and thermal expansion of ocean water. As warmer temperatures cause ice to melt, the water enters the oceans, increasing sea levels. Additionally, the oceans absorb heat, causing the water to expand and take up more space. Since 1880, the global average sea level has risen by 8-9 inches (21-24cm), and scientists predict it could rise another foot (0.3m) or more by the end of the century.

Global Perspective: Sinking Cities Worldwide

A 2020 study examined 48 coastal cities globally and found that they are sinking at varying speeds. While Jakarta experiences sinking rates of up to 11cm per year, Tianjin in China sees rates as high as 18cm per year. The combination of land sinking and climate change-induced sea level rise can lead to more severe and prolonged floods if mitigation measures are not implemented.

Reasons for Sinking and the Role of Urbanization

While groundwater extraction is a primary driver of sinking in many cities, other factors contribute as well. Compressible soil, as found in Jakarta, Manila, and Hong Kong, can exacerbate sinking. Land reclamation, where land is added to the edge of the ocean for infrastructure development, can also cause sinking. Urbanization in Asian cities contributes to groundwater depletion. As populations grow, so does the demand for water. In cities where piped water supply is inadequate, residents often drill wells and extract groundwater, further contributing to the problem.

Solutions and Mitigation Strategies

Government Initiatives

• Indonesia: The Indonesian government recognizes groundwater extraction as a cause of sinking and has started to ban it in some areas. They are also planning to move the capital to another island. However, this plan raises concerns about the environmental impact on the new capital region.
• Tokyo: Tokyo implemented strict regulations on groundwater pumping in the 1970s, which has slowed down sinking. To provide water to its residents, Tokyo built dams and reservoirs and purifies surface water for distribution.
• Shanghai: Shanghai has successfully implemented groundwater recharge by injecting purified surface water into groundwater wells, replenishing the water that has been extracted. Los Angeles has adopted similar strategies.

Community-Based Solutions: Sponge Cities

Scientists suggest the concept of "sponge cities" as a solution. Sponge cities incorporate green spaces and permeable surfaces to absorb rainwater and surface water, allowing it to naturally flow into the ground and recharge the compacted land. This approach can be implemented by both governments and communities.

Nature-Based Solutions: Floating Structures

Kunle Adeyemi, an architect and founder of the African Water Cities Project, designed a floating school in Lagos. His "Makoko floating system" is a prefabricated, easy-to-assemble floating structure built from timber and bamboo. These structures can adapt to the conditions of water and offer a resilient future for coastal cities facing challenges from flooding.

Conclusion

Sinking cities present a complex challenge driven by a combination of natural factors, human activities, and climate change. While the situation can seem dire, various solutions are being developed and implemented around the world. These include government regulations, infrastructure projects, innovative urban planning concepts like sponge cities, and nature-based solutions like floating structures. By understanding the causes of sinking and adopting appropriate mitigation strategies, cities can work towards a more sustainable and resilient future.