A landslide struck Pasirlangu village in Cisarua district, West Bandung Regency, on 24 January 2026. Indonesia's Geological Agency said the main trigger was heavy rainfall before and during the event, which raised pore water pressure, reduced the shear strength of the soil and led to slope failure. The area consists of old, weathered volcanic rock with steep slopes, fractures and faults, and lies in a medium ground movement susceptibility zone. The risk was increased by slope cutting for housing and roads and by inadequate surface drainage (Putra, 2026). By day 20 of the search, joint rescue teams had recovered 101 body bags, 83 of them already identified (Febiari, 2026).
The rainy season is not over. At a webinar on 10 February 2026, the national weather agency BMKG said West Java has the highest potential for hydrometeorological disasters of any province, followed by Central and East Java, and data from the disaster agency BNPB for 2010 to 2025 show a rising trend in floods and landslides (Firmansyah, 2026). For workplaces in hilly terrain, such as factories, mines, plantations, road projects and worker housing, the question is practical: what kind of early warning is good enough to stop work or evacuate people?
How We Compare
We compare three approaches against five criteria: area coverage, location precision, lead time before an event, cost and maintenance, and the organisation needed to act on a warning.
Regional Maps and Forecasts
The first approach relies on government ground movement susceptibility maps and weather forecasts. A review of 26 regional, national and global landslide early warning systems since 1977 found that such systems use rainfall thresholds, distributed slope stability models or soil water balance models, and that most rest on susceptibility zoning (Guzzetti et al., 2020). Their strength is wide coverage at no cost to the company. Their weakness is coarse resolution: they cannot say which slope will fail. The same review noted that there is still no accepted standard for testing the performance and forecasting skill of these systems (Guzzetti et al., 2020).
On-Site Rain Thresholds
The second approach installs a rain gauge at the work site and sets rainfall thresholds for staged action. It is cheap and site specific. Reliable thresholds, however, need a local history of events, and rain is not the only trigger. The Cisarua case shows the role of rock condition, slope angle, slope cutting and drainage alongside rainfall (Putra, 2026).
Integrated Slope Monitoring
The third approach installs instruments that track slope movement, such as extensometers, combined with a community-based response system. A methodology developed in Indonesia sets out seven sub-systems: risk assessment and mapping, dissemination and communication, a disaster preparedness team, evacuation maps and routes, standard operating procedures, monitoring and early warning including drills, and local commitment to operation and maintenance (Fathani et al., 2016). The approach was later formalised as Indonesian National Standard SNI 8235:2017 on ground movement early warning systems, and an evaluation of a system built by the technology agency BPPT in Jatiradio, Cililin, West Bandung, concluded that it complied with that standard (Sudiana, 2020). Its strength is that ground movement is measured directly and warnings are linked to action. Its weaknesses are higher installation and maintenance costs, and instruments are placed only on slopes already known to be unstable.
Our Assessment
The three approaches do not replace one another. Regional maps tell us where to raise vigilance, local rain thresholds tell us when, and slope monitoring tells us whether a particular slope is actually moving. Cisarua is a reminder that even a medium susceptibility zone can move when slopes are disturbed and heavy rain persists (Putra, 2026), so a zone label alone is not a sufficient basis for decisions at site level.
In our view the weakest point is usually not the instrument but the chain of action after a warning. Of the seven sub-systems in Fathani et al. (2016), only one is hardware; the other six concern people, procedures and commitment. Since no accepted standard yet exists for testing warning system performance (Guzzetti et al., 2020), companies should record each warning and what followed, so that thresholds and procedures improve from their own experience.
Recommended Steps
- Map slopes in and around the work site, including worker housing and access roads, against susceptibility maps.
- Install a simple rain gauge and set staged actions, for example alert, stop work near slopes, then evacuate.
- For slopes already showing cracks or seepage, consider movement monitoring and a geotechnical study.
- Write it all into the emergency response procedure with clear responsibilities, and rehearse it in drills before the peak of the rainy season.
How Nusa Safety Helps
Nusa Safety helps companies build preparedness that is linked to decisions on the ground, from engineering studies and risk assessment and the development of emergency SOPs and technical guidelines to emergency preparedness training and drills for site teams. Certificates issued by Nusa Safety are internal training certificates.
This article is general information and not legal or professional advice for any specific case.
References
- Fathani, T. F., Karnawati, D., & Wilopo, W. (2016). An integrated methodology to develop a standard for landslide early warning systems. Natural Hazards and Earth System Sciences, 16(9), 2123-2135. https://doi.org/10.5194/nhess-16-2123-2016
- Febiari, S. (2026, February 12). Tim SAR evakuasi 101 kantong jenazah korban longsor Cisarua, 83 teridentifikasi [SAR team recovers 101 body bags of Cisarua landslide victims, 83 identified]. Metrotvnews.com. https://www.metrotvnews.com/read/koGCajPe-tim-sar-evakuasi-101-kantong-jenazah-korban-longsor-cisarua-83-teridentifikasi
- Firmansyah, M. (2026, February 11). Hujan ekstrem makin meningkat, Jawa Barat berpotensi paling rentan bencana [Extreme rain is increasing, and West Java is potentially the most disaster-prone]. Kompas.com. https://lestari.kompas.com/read/2026/02/11/102700086/hujan-ekstrem-makin-meningkat-jawa-barat-berpotensi-paling-rentan-bencana
- Guzzetti, F., Gariano, S. L., Peruccacci, S., Brunetti, M. T., Marchesini, I., Rossi, M., & Melillo, M. (2020). Geographical landslide early warning systems. Earth-Science Reviews, 200, 102973. https://doi.org/10.1016/j.earscirev.2019.102973
- Putra, F. F. S. (2026, January 26). Badan Geologi ingatkan ancaman longsor susulan di Cisarua Bandung Barat [Geological Agency warns of follow-up landslides in Cisarua, West Bandung]. Investortrust.id. https://investortrust.id/national/92483/badan-geologi-ingatkan-ancaman-longsor-susulan-di-cisarua-bandung-barat
- Sudiana, N. (2020). Evaluasi penerapan sistem peringatan dini bencana longsor di Kampung Jatiradio, Desa Cililin, Kecamatan Cililin, Kabupaten Bandung Barat [Evaluation of a landslide early warning system in Jatiradio, Cililin, West Bandung]. Jurnal Alami: Jurnal Teknologi Reduksi Risiko Bencana, 4(1), 9-18. https://doi.org/10.29122/alami.v4i1.4035
