Every year, the rainy season in the Chittagong Metropolitan Area (CMA), Bangladesh brings news of human causalities and property damage caused by landslides. Residents of the area can easily point out 57 locations of landslides that have occurred between 1982 and 2014. The worst landslide to hit the area was in 2007, killing 127 people in Lebubagan, CMA. In 2011, a landslide caused by a wall collapse in Lalkhan Bazaar area, killed 17 people.
Abdur Rahim, a victim from the Lebubagan area, described the landslide of 2007: “It rained continuously for a week and then, one morning, the hills fell apart in quick succession from three sides. People were trapped and 18 people died on the spot.” Landslides in Chittagong are mainly caused by continuous torrential rainfall fuelled by the development of residential houses on dangerous hill-slopes. The increasing population pressure and rapid development of urban settlements in the hills will aggravate the risk of landslide disasters in the future. Landslide warnings were traditionally conveyed through a loud speaker a couple of hours before a disaster event. Predictions were based on rainfall observations over the previous few days, without using any scientific methods. This method did not save many lives or protect property, as it did not provide enough time for rescue and relief teams to prepare and organize. For the vulnerable communities in the CMA, a landslide early warning system would reduce the associated risks.
The research team talks to residents of informal settlements in Chittagong. The majority of people affected by landslides lives in informal settlements.
To address this issue, the Bangladesh University of Engineering and Technology-Japan Institute of Disaster Prevention and Urban Safety (BUET-JIDPUS) took the initiative in 2014 to develop an information system that can provide landslide early warning alerts to vulnerable communities. The project is administered by the International Centre for Integrated Mountain Development (ICIMOD) under it SERVIR-Himalaya initiative. One of the main outcomes of the project is the landslide early warning system hosted at www.landslidebd.com. The system sends alert messages to registered subscribers about probable landslides five days before the predicted event. The landslide prediction is based on predicted rainfall data from www.worldweatheronline.com, a UK-based private company. The website also contains probable landslide location maps along with precipitation data for the last 30 days. Different features of the site provide additional information on the project study area. Users can download reports on rainfall pattern analysis, land cover modelling, community vulnerability, soil investigation, slope stability, and web-GIS warnings, among other things. The site also provides an overview of the landslide risk scenario through documentary videos, field level photographs and links landslide devastation in the CMA. The website has already been subscribed to by the Chittagong Development Authority, Chittagong City Corporation, Department of Environment, and Fire Service, which are involved in rescue and relief efforts.
This study found that the majority of victims of landslide incidents live in informal settlements and are generally migrants who have come from other parts of Bangladesh in search of better livelihood options. Most work as labourers on construction sites, rickshaw pullers, auto rickshaw drivers, or retail businessman. Rents in such places are low, but buildings often do not meet the standards set by the government.
The landslide early warning system developed by the BUET-JIDPUS will help authorities to reach out to these communities on time to alert and relocate them. The authorities in the CMA recognize the need for an early warning system. “An early warning system for landslides is a great initiative towards a planned Chittagong city, which can reduce the associated risks,” said Abdus Salam, Chairman of the Chittagong Development Authority.
The land cover modelling conducted by this project found that the CMA went through a massive change between 1990 and 2010 due to an increase in the urban built-up area. The soil is sandy and the areas under additional pressure from land cover change and deforestation. As a result, rainfall for 5 to 7 consecutive days can trigger the hills to give way. The study found that the pressure on hill slopes can be reduced if people are relocated permanently. Accordingly, the government has initiated a hill protection policy and land use control measures. However, such measures take years to put in place. The immediate response to address the issue is to raise awareness, provide an effective early warning system, and construct retaining walls around the hills to reduce the risk.
As part of the project, BUET-JIDPUS carried out landslide susceptibility and slope stability modelling in the CMA. The outcome of the slope stability modelling under the project provides information on slope and geo-physical characteristics, as well as soil composition properties. The data collected from the landslide risk sensitivity modelling can help authorities to carry out risk sensitive land use planning for the CMA.
The outcome of the project and recommendations are being shared with the Chittagong Development Authority, Chittagong City Corporation, Department of Environment, Bangladesh Institute of Planners, Institute of Engineers Bangladesh, Chittagong University of Engineering and Technology, BUET, Dhaka University and local communities. The project is expected to help raise institutional awareness about the disaster risk to reduce future damage from landslide disasters in the CMA.
Map showing the areas with landslide probability for five days in advance