Java Island, located in Indonesia, is the country’s main island, with a population of 150 million, more than half the population of the country. There are at least four big cities located on the island that have seen fast development in the last 30 years. The land subsidence (LS) issue caused by groundwater overexploitation, compaction, and geological setting, has been known on the island for more than 20 years. However, past studies have mostly focused on one particular important area, while the big picture of LS on the whole island is often overlooked. This study utilized Sentinel-1 Synthetic Aperture Radar (SAR) data from 2017 to 2023, analyzed using Small Baseline Subset (SBAS) interferometry, to map LS across Java Island. We used DEMNAS to eliminate the topographic signal. We found ten regions with a noticeable LS rate, affecting nearly 60 million people who reside in the LS zones, namely, Serang, Greater Jakarta, Cianjur, Bandung, Cirebon, Brebes and Tegal, Pekalongan, Greater Semarang, Surabaya, and Sidoardjo. The highest rates and the large coverage of LS were observed in Greater Jakarta (up to 150 mm/year), Bandung (200 mm/year), Semarang (160 mm/year), and Pekalongan (up to 110 mm/year). LS was also detected in smaller areas or districts, such as Serang, Cianjur, Cirebon, Brebes, Tegal, Surabaya, and Sidoarjo, with rates ranging from 60 to 140 mm/year. The two areas of Cianjur and Brebes, which have never been mentioned in previous studies, show LS rates of about 80 mm/year and 70 mm/year, respectively. The LS rate in all areas was shown to be linear over time, except in Pekalongan, which shows rate deflation after 2021. We also found that most affected regions are urban and industrial zones, indicating a strong correlation with anthropogenic activities. LS leads to widespread socioeconomic and environmental impacts, including damage to infrastructure, increased flooding, and reduced groundwater capacity.

Indigenous knowledge is proven to be one of the foundations of sustainable land and marine management. While indigenous knowledge is acknowledged as of important factors on maintenance of biodiversity of the planet, it also ensures the sustenance of social and economic system of indigenous community. To facilitate the application of indigenous knowledge on management of customary forest in Indonesia, since 2012, the Government of Indonesia has been providing formal access for indigenous communities to their forests to maintain forest sustainability and to enhance the welfare of indigenous community. Nonetheless, the achievement of sustainable development goals in the scope of forest and conservation area management is threatened by various competing interests and power imbalance, which mostly leads to conversion of naturally vegetated area, as well as the inability of the community to integrate new economic opportunities to its institution. Moreover, the Government of Indonesia has not been regulating the involvement of indigenous community on the management of conservation area. Most importantly, such a program provides no reference on indigenous community, especially on the assessment of authenticity of indigenous community’s forest. Cultural space methodology may fill the aforementioned gaps. The methodology was developed based on the notion of cultural space and land administration, particularly the people-and-land/marine space relationship. Moreover, such a methodology was also constructed based on the experiences of agricultural and maritime communities in Indonesia on the administration of their territories. The methodology provides a procedure to convert information on the interrelation of indigenous community, its cultural space in forest and conservation area, and indigenous knowledge into geospatial information and data that represent the cultural space unit as a geographic feature. Therefore, such methodology may be utilised to assess the authenticity of a long-existing relationship between a community, especially an indigenous one, and its land, particularly that serves conservational function.

In recent years, Synthetic Aperture Radar (SAR) technology has been widely used to observe volcano deformation, which is associated with its activity. We used 26 images of ALOS PALSAR (Advanced Land Observing Satellite Phased Array type L-band Synthetic Aperture Radar) data, spanning the range from 2006 to 2011, to create deformation maps of the Kelud Volcano. Here, a Small Baseline Subset (SBAS) time series inversion algorithm is used to reveal the dynamics of the deformation in the Kelud volcano. A line-of-sight (LOS) change associated with uplift patterns was observed prior to the 2007 eruption inside the crater and was followed by subsidence afterwards. Our result shows that the relaxation period stopped around January-February 2009, and the uplift pattern returned until April 2011 with the deformation magnitude as large as 20 cm. A large deformation occurred from May to October 2009, but it was not followed by an eruption. This uplift pattern may indicate accumulation of energy in the plugged conduit and is expected to be the precursor of an eruption. We argue that this might be the onset of an unrest period prior to the 2014 eruption, although more study and evidence needs to be done to support the argument.

Flooding in tropical coastal cities is increasing due to urbanization and land subsidence, which reduce hydraulic gradients and cause gravity drainage systems to fail. In the Loji subsystem, land subsidence of approximately 1.86 cm/year has caused parts of the area to fall below sea level, exacerbating flooding. Conventional infrastructure (grey infrastructure) is ineffective because it merely accelerates flow without increasing infiltration and recharge. This study develops a Low Impact Development (LID) framework based on PCSWMM modeling through three scenarios: existing, partial, and integrated. Results show that the integrated scenario is the most optimal, with peak flow reductions of 22%, 19%, 18%, and 17% for return periods of 2–20 years, and a reduction in runoff volume of up to ±22%. Flood depth distribution also shifts from >0.5 m to <0.3 m. However, LID effectiveness decreases during extreme rainfall. This study confirms that LID can enhance infiltration and recharge, serving as an indirect mechanism for controlling subsidence. It offers a new nature-based approach to support zero runoff policies in vulnerable coastal areas.

Indigenous knowledge and associated indigenous resource management practices are at the root of sustainable land and marine management. Typically, they point to the necessity of maintaining biodiversity and of ensuring the sustenance of social and economic systems, which benefit the well-being of indigenous communities. Conscious of these core attributes, the Government of Indonesia has enabled formal access for indigenous communities to forests for their livelihoods. Nonetheless, meeting the sustainable development goals through such forest management and conservation in Indonesia is threatened by various competing interests and power imbalances. These lead to the disproportionate conversion of naturally vegetated areas, as well as the inability of communities to benefit from economic opportunities. Moreover, the Government of Indonesia has insufficiently regulated the utilisation of indigenous knowledge to conserve the forest areas. This creates a policy design and implementation gap which is not properly understood or addressed. In this conceptual article, we posit that applying cultural space methodology fills the gaps. This methodology combines cultural space and land administration concepts and connects people to land and marine space. This article discusses how and why using the methodology proves to be effective for agricultural and maritime communities in Indonesia and helps to reform the administration capacities of the territories. It identifies and assesses people and land/marine space relationships by the existence of (1) knowledge, practices, and/or objects that represent the relationship, (2) the social, economic, and environmental function of space for the community, and (3) administration of the forest and conservation areas. The methodology also provides a procedure to convert information on the interrelation of the indigenous community, its cultural space in the forest and conservation areas, and indigenous knowledge into geospatial information and data that represent the cultural space unit as a geographic feature.