Asia’s Sinking Cities: Indonesia

The current situation is plain as day. As the climate change worsens, global sea level rise (SLR) continues to climb. Meanwhile, dramatic increase in population and poor urban planning drive Indonesian coastal cities such as Jakarta to sink further every year. The question is, what can we do to mitigate the foreseeable impacts? Even better, how can we begin to adapt?

In 2019, the Indonesian government made a bold decision to move the capital city from Jakarta in the densely populated Java Island, to the eastern part of the neighboring Island of Kalimantan (Borneo). The rapidly sinking megacity has been one of the main drivers.

Jakarta is currently the fastest-sinking city in Indonesia—and on earth. While the city proper sinks at an average rate of 1-15 centimetres per year, some areas have sunk more than 4 metres since the 1970s. The coastal area of North Jakarta, in particular, has sunk 2.5 metres in the past decade and will continue to do so at the rate of 25 centimetres per year. This gradual sinking process is called subsidence.

Jakarta’s land subsidence through the years


Source: Dr. Heri Andreas, Faculty of Earth Sciences and Technology, Bandung Institute of Technology (ITB). Visualization by BBC. Note: 2025 and 2050 predictions are based on research by Dr. Heri Andreas.

Based on ITB’s model, 2025 will see almost the entirety of North Jakarta submerged under water. That is a real threat to at least 2 million people who have built a home there. Considering that almost half of the city proper is already below sea level, it is not exactly hard to assume that more and more areas will eventually follow suit. That includes many islands that form Jakarta’s off coast municipality of Kepulauan Seribu.

Unfortunately for Indonesia, Jakarta is just one among many.

Major cities along the north coast of Java Island (Pantura) are losing their shoreline at an alarming rate. Throughout 2013-2017, the Central Java city of Brebes, Demak, and the regional capital, Semarang, have to witness 8,023 hectares of their combined land disappear to the sea. That is about 11,000 times the size of a football field. 

Most of the disappearing coastline has been attributed to sea abrasion due to the climate-induced rising sea level. However, 13 Central Java cities along the north coast have also been steadily sinking in the past decades. Between 2015-2020, Semarang has sunk 0.9-6 centimetres per year, while its neighboring Pekalongan has it worse with 2.1-11 centimetres land subsidence per year. Local authorities found that excessive extraction of groundwater has played a major part in this phenomenon.

“If the projection is only focused on the effects of climate change alone, then the resulting impact will not be too severe. The same thing applies, if the projection is focused only on land subsidence, then the analysis cannot be used on a global or regional scale.”

Eddy Hermawan, Research Professor in Meteorology at the Aviation and Space Research Organization, Indonesian National Research and Innovation Agency (BRIN)

But how common is it for a coastal city to sink?

Sinking city is a global trend, but even more so in SE Asia

Unfortunately, sinking coastal and delta cities is a worldwide phenomenon, especially within the past century. 

Parts of Tokyo, Japan, have reported 4 metres subsidence throughout the 20th century. Other big cities such as Shanghai (China), Bangkok (Thailand), Dhaka (Bangladesh), and New Orleans (United States) have also witnessed land subsidence of 2 metres or more. Dhaka (Bangladesh), Lagos (Nigeria), and even Venice (Italy) have also experienced some significant degree of the phenomenon. 

Due to their riches and oftentimes strategic position, river deltas and floodplains have attracted settlers since the dawn of civilization. In 2017, about 40% of the world’s population—close to 2.4 billion people—live within 100 kilometres of a coastline. Around 1 billion of them live in areas that are 10 metres above sea level or even less. 

Most of the time, inhabitants of such low-lying lands are aware of several natural threats. One of which is flooding, which originates from either the river or the sea. In the past, accumulated upstream sediments as well as brackish water vegetation, such as mangrove, provided enough buffers against said risks. Today, these natural defense mechanisms are an extreme rarity. 

With a surging population, comes an increasing demand for housing and infrastructures. Concrete structures eventually replace what is formerly vegetated river bank, swamp, or empty field. At the same time, residents rely on the extraction of underground resources, such as groundwater in the aquifer, in order to survive. Overtime, it creates subsidence which causes the land surface to sink.

Meanwhile, worsening climate change increases global sea level rise (SLR) in two ways: ice/glacier melt and thermal expansion. 

As laws of physics dictate, an increase in temperature will melt ice and expand the volume of a material. That is basically what happens with glaciers in both poles and the ocean in general, but on a much grander scale. In addition to that, extreme weather events will also increase in both frequency and intensity, especially in coastal areas.

It is no wonder that many Southeast Asian regions have been disproportionately affected by the sinking cities phenomenon. Cities like Bangkok, Manila, Ho Chi Minh City, and Jakarta have seen massive economic development and rapid growth in population density within the recent decades. 

The speed and the scale of which these changes are happening, however, are not always accompanied by appropriate planning of urban and  spatial development, as well as disaster mitigation. The result is often a sprawling city that is largely unprepared for the looming threats from surrounding elements. 

Within the 1901-2010 period alone, global SLR has reached up to 0.19 metres. Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC), which is part of the Fifth Assessment Report (AR5) by Intergovernmental Panel on Climate Change (IPCC), has offered several SLR scenarios. Under the most optimistic one, global mean sea level will only reach 0.28-0.60 metres by 2100. In the High Emission Scenario, it will reach 0.52-0.98 metres. Many experts, however, agree that we are ultimately heading to the SLR level of 2 metres by the end of the century. 

By then, more than 200 million people in the world will be living below sea level. Southeast Asian countries such as Vietnam, Thailand, the Philippines, and Indonesia will see about 38 million of those deeply impacted populations. That is a little more than the number of people currently living in the Greater Jakarta metropolitan area (Jabodetabek).

The general rule of thumb is, for each 2.5 centimetres of SLR, 2.5 metres of beach will be lost. This has not yet, however, put land subsidence into the equation. In order to understand the true damage big coastal cities have been and are suffering, one has to observe the rate of relative sea level rise, which is the combination of vertical land motion—in this case, subsidence—and SLR.

Relative sea level rise all over the world

Source: Nicholls et al., via The Conversation UK.

On average, coastal areas all over the world are experiencing relative sea level rise of less than 3 millimetres per year. However, residents of coastal cities witness relative sea level rise that is about three times higher (8-10 millimetres per year). Off the coast of Semarang, the number is 7.8 millimetres per year. In Jakarta’s case, relative sea level rise ranges between an alarming 50-100 millimeters per year. That is a hundred times the level of absolute global sea level rise.

But how does the capital Jakarta, in particular, come to be in its current predicament?

The mechanics of a sinking Jakarta

Jakarta, too, has been sinking under the combined force of pre-existing geological risks, land exploitation induced by human activities, and rising sea level caused by global warming for years. It is a problem as old as time, so to speak. Yet due to its relatively unique circumstances, the sinking of Jakarta has become so bad that fixing it feels almost like an impossibility.

To begin with, today’s mainland Jakarta covers an area of 662,33 km² that was originally a vast swampy land at Ciliwung River delta. Aside from Ciliwung, there are twelve more rivers flowing through the region and into the Java Sea. That naturally makes the area prone to flooding, both from the rivers and the sea, as well as to land subsidence. Its location within the Pacific Ring of Fire also makes the area prone to bouts of tectonic and volcanic earthquakes.

These underlying risks are multiplying as the city grows upwards and outwards. Jakarta is now home for more than 10,56 million people based on the latest 2020 census. If the greater metropolitan area (Jabodetabek) is included, the total population count will easily exceed 30 million. In spite of that, around 60% of Jakarta’s residents currently still have no access to clean piped water.

As a result, millions of households are left to survive by digging wells and installing pumps deep into the aquifers—porous rocks or sediments that hold groundwater. Unfortunately, they are not the only ones who engage in this cheaper but illegal means of acquiring clean water. According to a study by the Indonesian Agency for the Assessment and Application of Technology (BPPT), many office buildings, hotels, and malls have also benefited from this practice. Meanwhile, the government lacks the capacity to properly conduct a widespread inspection and monitoring of such activities.

As the excessive exploitation of groundwater continues, the soil eventually compacts and gradually collapses on itself, bringing the land surface down along with everything built on it. On top of that, nearly 90% of the city landscape is covered in buildings and concrete. Thus, the soil can no longer absorb rain water to replenish the depleting aquifer. The result is a devastating 6 centimetres of land subsidence per year.

Jakarta changing landscape (1990 vs 2019)

Source: NASA Earth Observatory

As observed by NASA’s satellite, Jakarta has undergone a large-scale development in the past few decades. The newly operated and still developing Mass Rapid Transit (MRT) and Light Rail Transit (LRT) transportation system are just the latest of infrastructure development in the city. Sadly, the weight of this ever expanding construction has also contributed in making Jakarta sink even lower. 

To be fair, this upsetting situation can be attributed to the way the Dutch colonists have built and ruled over the city for more than two centuries.

In the early 1600s, Dutch East Indies Company (VOC) took over the strategic port town of Jayakarta from the Sultanate of Banten and razed it to the ground. Upon the ruin, they built a new city called Batavia, complete with segregating grids and canals based on Dutch urban planning system of the era.  

Map of Batavia in 1667.
Collection of Tropenmuseum, part of the National Museum of World Cultures. CC BY-SA 3.0.

When the deteriorating canals eventually became the breeding ground for diseases such as cholera and malaria, the wealthier Dutch moved further south to escape the unhealthy environment. There, they set up a new city with a brand new centralized piped water supply system that provided their households with clean water. This, however, did not extend to most indigenous people living outside of the Dutch residential areas. They were basically left to resort to street vendors and even the neglected canals for water supply. 

Ultimately, access to clean water became a new means to segregate between the colonist and the colonized. The beginning of Jakarta’s overreliance on groundwater extraction began. And while the Dutch have left Jakarta—and the country—for good since 1949, their legacy remains.

It gets worse

What transpires in Jakarta has set into motion a chain of unfortunate events. Many of which are unintended but have devastating consequences all the same.

Coastal communities, such as those in Muara Baru and Muara Angke in North Jakarta or in the Islands of Kepulauan Seribu, are the very first to suffer. Lower-income fishing communities, whose livelihood depends heavily on the sea, make up a big portion of inhabitants in these areas. 

When the water gets too high, they have been forced to abandon their old homes and move further and further inland, where informal settlements called kampong are already overcrowded. Those who lack the resources to rebuild their houses have resorted to sleeping on their boats. Even makeshift bridges have had to be built to connect one neighborhood to another.

As preemptive measures, Jakarta authority has cooperated with Dutch and South Korean governments to build a 32 kilometers outer sea wall across Jakarta Bay along with 17 artificial islands. The $40 billion (Rp 570.2 billion) project, dubbed the Great Garuda, is set to form a giant bird-shaped barrier between the rising Java Sea and the mainland residents. As per August 2021, the project still sits at the level of pre-designing and fund consolidation. 

In 2014, The Indonesian Ministry of Public Works and Housing had set a goal to construct 120 kilometres-long beach embankment to prevent tidal flood (banjir rob) from inundating the seashore kampongs. Only about 13 kilometres of it has been built so far. But as the ground keeps sinking, so does the structure. In several spots, another metre has been added to the embankment’s height each year, but the efforts barely keep the sea water from spilling in.

To make matters worse, climate change makes the weather events often more severe. More frequent violent storms push the existing embankment to its limit. The already intense 300 days of rain can turn fatal during monsoon and heavy rain season, such as one in 2007 and more recently, in the new year of 2020. The mere several hours of torrential rain resulted in 66 deaths and prompted 170,000 people to flee their home.

Even though major floods have become somewhat common occurrences beginning in 1990, nobody in Jakarta could really predict how severe each flooding would be. 

That is because not only the rain intensity has become a defining factor. The consistent amount of sediments and trash clogging the waterways, in many cases, has also rendered the drainage system useless. Not even mentioning how a prolonged water locked situation would lead to diseases like dengue & typhoid.

The forecasted future (and how to deal with it)

Time is running out for Jakarta and other major coastal cities in Indonesia.

The “easy fix” will be to continuously pile up more tetrapods or build even higher dykes along the coast. But as pointed out by three Dutch non-profit groups in 2017, even the Great Garuda giant sea wall could only buy 20-30 years for Jakarta to find a long-term, fixed solution to the city’s land subsidence. That is not yet to mention the fishing communities’ concern that their daily catch will be heavily affected by the construction.

The obvious solution will be to stop the residents from taking up more underground water. At the same time, each city must designate at least 30% of its territory for green spaces, to allow rainwater to be absorbed back into the aquifer. River, canals, and other drainages also need to be constantly cleaned out of trash and sediments so that excess rain water can easily flow to the sea. Strictly limiting construction projects in coastal areas and other subsidence-prone zones will also greatly help lessen the weight from pressuring down the soil further. 

The myriads of solutions would spell a significant amount of work and a big budget to cover. Time and other resources also need to be channelled into monitoring efforts, enforcement of regulation, and public education. Last but not least, aside from NGOs, research institutes, and other concerning partners, local residents must also be involved in the decision making. Empowered citizens will be part of the solution, not the problem.

Until further and more decisive actions are made, the coastal population will keep on living on borrowed time. Vacating the premises and fleeing elsewhere, just like what the Indonesian government is planning for the capital, might be the only future left for many. 


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Researcher at Climate Tracker

Has been working at the intersection of Communication, Sciences and Diplomacy for more than five years. A sweet tooth and occasionally dabbles in voice-over. Working alternately from Jakarta and Yogyakarta. Also speaks Indonesian, Javanese and some French.