Landslide is a regular hydro-geological hazard in Bangladesh that poses a severe threat to local people especially people who lives in the urban hilly areas in Chittagong and Chittagong hill tracts(CHT). It is a very common phenomenon is this region due to its geological structure but there are multiple factors that influences the landslides occurring here. Some of the cause of landslide in these areas are influenced by various factors including rainfall, soil characteristics, localgeology, topography, climate, and land use/land cover type. Though landslide occurs here frequently during the monsoon and post-monsoon season, the local people did not consider this phenomenon as a threat in the previous decades. The history and culture of Ethnic Community of CHT alongside their indigenous knowledge on the area made them adaptive to the natural phenomenon of landslide not a big threat for their lives and livelihoods previously.
But in more recent decades we have seen that landslide has become a greater threat and a devastating disaster to the people living in this region, especially in the CHT region. The casualties from landslides are becoming increasingly common here in the mountainous districts of Bangladesh, a former conflict zone, as local indigenous communities and landless settlers from other parts of the country rush to build homes on vacant but risky slopes.
It is seen that Chittagong division has suffered 12 landslides with a death toll of 633 and damage of thousands ofhomes between the years 1999 and 2019.
The annual monsoon season, which begins in June and lasts throughout October, brings heavy rainfall that can soak the slippery hillsides and dislodge unstable clay soil. Alongside the soil structure becoming weaker due to heavy rainfall in the hilly areas, the impact of Climate change is expected to make the extreme weather more volatile and intense, leading to increase of the likelihood of landslides.
FOREWARN Bangladesh alongside Caritas Bangladesh jointly made a study to identify the socio-economic vulnerability alongside landslide susceptibility, forecasting landslide and possible interventions that would help the people working in these areas to take early actions to mitigate the risks. The objective of the study included finding the most vulnerable sites for landslides in a total of eight Upazilas of both Bandarban and Rangamati by using composite vulnerability index and also design Early Actions and Protocol to reduce the loss of lives and property due to landslide incidence.
Causes of Landslide in Bangladesh
Natural causes are the major triggering mechanism for landslides either singly or in combination with water pressure and seismic activity. Excessive rainfall results in an increase of groundwater pressure which destabilizes the slope of the hill. The new settlements create disturbance to the natural drainage system and destabilize slopes also. Many studies address that human activities such as hill cutting without considering the proper slope and deforestation of the hilly area, especially deep-rooted vegetation reducing the strength of the soil particle are the primary causes of a landslide in this area.
Historical Events of Landslide
During the last five decades, Chittagong has suffered 12 major landslides. The first recorded landslide in this region was in 1968, before independence. The landslide took place in KaptaiChandraghona road section and caused 2 people to be wounded. Considering the previous history of Bangladesh, landslides in CHT turned deadly. In 1999 as 17 people died in that year. Highest number of fatalities and casualties of assets were recorded in 2007 and 2017. In 2007, the landslide resulted in 136 deaths and affected 1.5 million people in the Rangamati, Bandarban and Chittagong area. Again, in June 2017 landslides had a death toll of 170 people and destroyed or damaged more than 40,000 homes.
Triggering Factors of Landslides
As part of the study, experts identified the triggering factors of Landslide in the country. Rainfall has been identified as the most impactful triggering factor for landslide in our country as per historical data analysis. Heavy rainfall in the hilly mountains in a short period of time leads to the soil structure to weaken and landslide occurs. Literature on landslide studies show that rainfall is the primary triggering factor of landslides, and it is statistically calculated that 100 mm of rainfall in 3 h, 200 mm in 24 h (1day) and 350 mm in 72 h (3 days) can be the threshold values of rainfall to initiate landslide occurrence. (Reshad et al, 2018).
Most Vulnerable Areas Identified in Bandarban and Rangamati
The study conducted by experts from different field identified the most vulnerable locations from Bandarban and Rangamati district based on the multi-dimensional analysis.The most vulnerable spots and the landslide susceptibility zones portray the condition of disaster risk induce by landslide in different Upazilas of the study area. As per the analysis Ruma, Rowangcchari, Sadar and Lama Upazila of Bandarban and Kaptai, Nainarcchar, Thanchi and KawkhaliUpazilaUpazila of Rangamati are found as the most vulnerable location.
Experts view for Risk Mitigation
Traditionally the indigenous communities of CHT adapted to the hilly region and landslide occurrences by avoiding steep slopes and building stilted homes that allowed excess water to pass under rather than through. Traditional housings in the area mostly used bamboo as core material for the structure of the house but as the bamboo became more expensive alongside the impact of urbanization in the region, more families are now opting for housing structures following urban houses. Leading to increased risk to landslides. Experts indicates that unplanned and rapid urbanization needs to be halted rather adaptive housing structure for hilly region should encouraged to local people.
Experts suggests that early warning and preparedness for landslide preparedness programme should be made alongside the advocacy for practicing traditional indigenous practices of local people. The local administrations have been working towards reducing the vulnerabilities of people and the report can help them to further take early action interventions prior the disaster occurs. The coordinated efforts from government, local, and non-governmental stakeholders can lead to a sustainable solution to landslides for local communities.
Marwa Tasnim is Partnership Officer, FOREWARN Bangladesh