In response to rapid land subsidence in Central Java, the Building with Nature Indonesia consortium released a Roadmap towards Adapting and Mitigating Land Subsidence in Central Java province, developed through ‘Water Dialogues’ with the Provincial Government and local stakeholders. Land subsidence is causing the sinking of the city of Semarang, the biggest city in Central Java, up to 13 cm/year. This is severely increasing flood risk for communities and massive economic damage, not only for Semarang, but also for the entire coastal stretch of the adjacent district of Demak.
With the rapid population growth and urbanization, coupled with the impacts from climate change, densification of the coastal area was not complemented by proper water management in Semarang and other cities in coastal lowlands. Industrial and other commercial activities that use a significant amount of water trigger excessive groundwater extraction and increasing surface load. External factors such as natural soil consolidation and tectonic activities have aggravated the situation which leads to an ever-increasing land subsidence rate in the near future.
Significant and visible impacts of land subsidence include coastal erosion and flooding, locally known as ‘rob’, and infrastructure damage. It also causes the degradation of healthy wetlands and limitations to restoration of mangroves such as in the adjacent rural district of Demak. Altogether, this increases the community’s vulnerability to extreme weather, and the loss of means to sustain livelihoods.
Up until now, measures to adapt and mitigate land subsidence across Central Java have been rather uncoordinated. A more transformative roadmap to address land subsidence was required with the active participation of multiple stakeholders and decentralized decision-making mechanisms. To mobilise inputs for the Land Subsidence Roadmap, Wetlands International coordinated extensive ‘Water Dialogues’ with authorities in Central Java, the city governments of Semarang and Demak, practitioners, academics and local communities in the north coast of Semarang and Demak.
As input for the development of this roadmap, technical expertise was delivered by Deltares, Witteveen+Bos, Kota Kita, Diponegoro University, and Institut Teknologi Bandung (ITB). Among others, Deltares conducted an assessment of the economic consequences under different subsidence scenarios. It shows that lowering subsidence by 50% can reduce the damage by 26% in Semarang and by 13% in Demak and by lowering the subsidence rate by 75%, the expected damage in Semarang and Demak is estimated to be reduced by 80% and 37% respectively.
Although it is a costly affair to invest in measures that reduce subsidence rates by 75%, the reduction in the economic losses shows that it is well worth the investment: $4,48 billion (63 trillion IDR) and $1,02 billion (14 trillion IDR) damages avoided for Semarang and Demak respectively.
The roadmap includes both short and long-term solutions for implementation by the governments. Potential measures that should be used in combination include the responsible use of water resources, piped drinking water supply, reduced water demand and recycling of available water. It further outlines actors and institutions involved as well as their roles in the adaptation and mitigation of land subsidence in Semarang and Demak, and a review of the current policy framework on addressing land subsidence in the study area. Lastly, in order to prompt the proposed strategies towards implementation, recommendations on national policy and institutional frameworks is expected to help local governments to operationalize the roadmap.
The development of this roadmap takes into account measures applied and proposed by the Building with Nature project in Demak, managed by Wetlands International, EcoShape and the Indonesian government as well as from the Water as Leverage project in Semarang and Integrated Coastal Zone Management (ICZM) of Central Java.
*The roadmap is currently provided as input from the consortium to Central Java Province Government, which is is awaiting guidance from the national level as a basis for legalizing and operationalizing the roadmap.
Assessment and Roadmap towards Adapting and Mitigation Land Subsidence in Central Java Provincedownload
Economic assessment of subsidence in Semarang and Demak, Indonesiadownload
Water Dialogues Mitigation and Adaptation Measures Information Sheetsdownload