A new study has revealed that humans are artificially extending city coastlines by constructing industrial ports and luxurious waterfront residences. According to the study, over 2,350 square kilometers of land (equivalent to 900 square miles or 40 Manhattans) has been added to major city coastlines in the past 20 years. This is the first-ever global evaluation of coastal land reclamation, the process of constructing new land or filling in coastal bodies of water to expand coastlines.

Satellite imagery analysis reveals 106 cities have expanded their coastline

Using satellite imagery, the researchers analyzed land changes in 135 cities with populations of at least one million. 106 of these cities have undergone some form of coastline expansion. The study found that coastal land reclamation is most prevalent in the Global South, with China, Indonesia, and the United Arab Emirates adding the most land area, primarily for port extension. On the other hand, only Los Angeles in the United States has noticeably added land in the past two decades, with a mere 0.29 square kilometers built.

Lead author Dhritiraj Sengupta, a physical geographer at the University of Southampton, and his team discovered that coastal land reclamation is driven by urban growth and industrialization, with a smaller portion of projects aimed at enhancing prestige. Approximately 70% of coastal land expansion has been carried out in low-lying regions that are at risk of extreme sea level rise by the end of the century. The authors predict that cities will continue to build these coastlines despite their unsustainable nature.

How new coastline land is created – and the problems it can cause to ecosystems

The process of creating new land is typically done by piling sediment in the ocean, building sea walls, or filling in wetlands near the coast. This requires large volumes of sediment and can disturb ecosystems permanently, with coastal wetlands being particularly affected. The study highlights the need to consider the environmental consequences of coastal land construction and to make responsible decisions about whether it is truly necessary.

The construction of new land can also contribute to pollution, alter sediment movement, and impact ocean-based economies such as fishing and tourism. Additionally, unequal access to the newly created shoreline can exacerbate class divisions. Reclamation can also harm distant ecosystems, as construction companies may quarry sand and clay from the seabed, destroying benthic ecosystems, due to a global shortage of sand.