The lost city of Jakarta?

Written by Udit Shankar

Home to over 10 million people, Jakarta is one of the largest and most densely populated cities in the world. The 13 rivers that flow through Jakarta mean that the land is generally swampy [1] and together with Jakarta’s low-lying nature, (average elevation of 8m above sea level) flooding is a regular occurrence. This problem is only exacerbated by the fact that Jakarta is also one of the fastest sinking cities in the world [2]. On average, the city sinks 1-15cm per annum and currently, almost half the city lies below sea level. North Jakarta is one of the worst affected areas, having sunk by 2.5m in just 10 years; twice the global average for megacities. At this rate, combined with rising sea levels as a result of climate change, 95% of North Jakarta will be entirely submerged by 2050 [3].

The alarming rate at which Jakarta is sinking can be partly explained by the unsustainable scale of groundwater extraction from aquifers [4]. Currently, groundwater extraction is unlicensed and unregulated allowing anyone from individual homeowners to large scale corporations to drill their own water extraction wells. In 1995, industries and private consumers were extracting more than 300 million cubic metres of groundwater per year, approximately three times the rate of replenishment. As a result, the land above these aquifers has begun to subside leaving the area more susceptible to flooding [2]. Since 1995, the replenishment rate has worsened further as the development of large concrete buildings has covered up natural drainage sites, whilst human waste and rubbish clog waterways. Despite the heavy monsoon rains, there is little contribution to groundwater sources due to high surface runoff into the sea [5]. Freshwater is provided by the water management authority, but can only cater to 40% of Jakarta’s water needs. Therefore, residents are left with no choice but to resort to unregulated abstraction from groundwater aquifers [6].

In Jakarta, the extraction of water from groundwater sources has gone beyond the Maximum Sustainable Scale. This is the point at which the rate of material throughput is theoretically equal to rate at which it can be regenerated. Any throughput increase beyond this point is unsustainable and breaches the biophysical limits of the affected ecosystem, thus depleting the resource [7]. Further increases in the level of material throughput may push this point beyond the Maximum Scale, an irrevocable loss of a critical ecosystem function. In order to protect the ecosystem function, the rate of extraction needs to be reduced to the Maximum Sustainable Scale and ideally, to the Optimal Scale. Established by socio-political influences, the Optimal Scale is the point where marginal costs equal the marginal benefits. Beyond this point, further groundwater extraction is unfavourable. It also serves as a safety margin by allowing for the occurrence of an unexpected natural or anthropogenic event without permitting throughput to reach an unsustainable level. Herein lies the need for the Optimal Scale which will prevent the depletion of, and ultimately replenish, the water table [8].

To limit land subsidence, Jakarta must make Optimal Scale a policy priority. The government must first define the Optimal Scale, with respect to groundwater. Once defined Jakarta can then work towards it, firstly, by addressing the issue of unregulated groundwater extraction. The local authority has only recently conceded the importance of this issue and have begun efforts to ensure that groundwater extraction rights are exclusive to licensed parties. Licensing has allowed the local authority to monitor and control the extraction rate [5]. Adang Saf Ahmad of the Ministry of Public Works and Housing has called for the local authority to further escalate regulation and ban the practice of groundwater extraction altogether [6]. Direct regulation, however, is no panacea [9]. Widespread illegal groundwater extraction occurs regularly, and so the local authority must also provide a reliable and commercially viable alternative for residents and businesses, as a means of shifting consumer preferences away from groundwater aquifers. This could be achieved through investments towards delivering an effective and efficient pipeline infrastructure [5].

Both regulatory reform and investment in infrastructure are long term solutions. In the short term, Jakarta could continue investing in flood defences, such as the Great Caruda, a 32km outer sea wall. Jan Jaap Brinkman, of the water research institute Deltares, raises concerns about the local authority seeing this as a sufficient long-term solution. Such measures provide an interim solution and may only delay the complete submergence of Jakarta by 20-30 years. Artificial recharge is an expensive, but effective technology that can replace groundwater deep at its source, and was used by Tokyo 50 years ago when it faced similar land subsidence [2]. Perhaps, a combination of these techniques could limit land subsidence, but the question remains however, can groundwater extraction rates be brought to sustainable levels and prevent Jakarta from becoming the next lost city?



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