Landslide is a motion of landmass (earth or debris) or downward movement of rocks on a slope and other factors, such as rainfall, earthquake, variation in water level, storm waves, or rapid erosion of streams are just a few examples of external stimuli that can cause shear stress to either increase or decrease quickly in slope-forming materials (Cruden, 1991). In hilly terrain areas around the world, landslides have resulted in numerous deaths and significant economic losses. It killed over 18,000 people and affected about 4.8 million people worldwide from 1998 to 2017 (UNISDR, 2018). In comparison to other continents, Asia is one of the most prone and vulnerable areas to landslides with the largest number of adverse accidents and deaths. In Asia, 3,456 disasters were recorded between 1970 and 2019, resulting in the deaths of 9,75,778 people and economic losses of US$ 1,204 billion (WMO, 2020), where the most vulnerable regions to landslide disasters are India, Nepal, China, and Japan in particular (Kirschbaum, et al., 2010; Petley, et al., 2005; WU, 2017). Bangladesh is the most recent addition to this list (CDMP-II, 2012), as this country is extremely vulnerable to natural disasters like cyclones, floods, storm surges, etc. due to its geographic position, terrain features, an abundance of rivers, coastline morphology, and monsoon climatic (Moniruzzaman, 2012).
Landslide disasters have been common in the past in the heavily settled area of Bangladesh, but in recent times, many landslides have resulted from intensified human activities, including hill cutting for slums and suburban housing construction (Ahmed, 2017). In the southeast part of Bangladesh, landslides have become a significant concern since the year of 2000 (Alam, 2020). For example, a series of devastating landslide incidents resulted in over 725 deaths in the Chittagong hill districts from 2000 to 2018 (Sultana, 2020). The impacts of the intense weather incidents (Khan, et al., 2020), demographic influence in flatlands, acceleration in urban growth, changes in hill slopes, deforestation, and a lack of cultural awareness have been classified as emerging challenges to mitigate the loss due to landslides at the national level (Alam, 2020).
Recently, Cox’s Bazar district has been categorized as a highly susceptible area to landslides. More specifically, Ukhiya and Teknaf Upazilas due to the changes in hill slopes for the development activities to accommodate a large number of Rohingya refugees. Since 25 August 2017, 655,000 Rohingya refugees had arrived in Cox’s Bazar district and the number had reached nearly 860,000 at the end of the year (UNOCHA, 2018; Imtiaz, 2018). According to the (ISCG, 2019) weekly report, 12 different landslides and erosion affected 98 refugees from 14–20 June and 4 different landslides and erosions affected 40 refugees from 20–27 June 2019. A continuous 14 inches of rainfall for 72 hours in July 2019, resulted in 26 landslides with one causality and 4,500 homeless occurred in the refugee camps of Cox’s Bazar, Bangladesh. Also in September 2019, 16 separate floods affected nearly 20,000 refugees including 2,000 refugees who had been displaced by new landslides (Jonathan, 2019).
It is necessary to identify the landslide risk zones to mitigate the probable loss in the area that contains a large number of local inhabitants as well as Rohingya refugees. As a result, landslide risk mapping can be a solution to reduce the damages (Regmi, et al., 2013). The interaction of certain dangers that make humans, entities, and ecosystems vulnerable and exposed are described as risks (Hoque, et al., 2019). The risk of a damaging landslide in a spatial (“where”) and temporal (“when”) sense, as well as the magnitude (“how large”) of the occurrence, can be described as a landslide hazard (Bui, et al., 2011), whereas the degree of damage determines the vulnerability which can be incurred by hazards to people's possessions, livelihoods, and the environment (Hoque, et al., 2017). In this study, the produced risk map provides crucial resources to help in sustainable construction and land use planning decisions. Furthermore, the successful use of these maps will significantly minimize landslide damage risk and other cost effects.
Qualitative maps are generated by adding weights to all variable landslide maps that rely on the expertise of the researcher, while quantitative methods include strategies to examine the relation between landslide criteria based on various models (Park, et al., 2012). Based on factors connected to the consequences of landslides and locations where historical landslides have occurred, both qualitative and quantitative approaches are tested (Park, et al., 2012; Ahmed, 2015). In landslide risk mapping, different methods are used with the key goal of designing landslide hazard zoning maps (Highland & Bobrowsky, 2008; Bathrellos, et al., 2012). Geographic Information System (GIS) and Remote Sensing (RS) techniques have recently gained popularity in landslide mapping. These methods are widely used for landslide susceptibility (Tehrani & Husken, 2019; Ahmed B., 2015; Jazouli, et al., 2019), hazard evaluation (Bachri & Shresta, 2010), and risk analysis (Dinesh, 2016), as well as landslide management (Kavzoglu, et al., 2014; Talaei, 2014). Analytical Hierarchy Process (AHP) developed by Thomas L. Saaty in 1970 has been used by many researchers to assess landslide risk worldwide (Boroumandi, et al., 2014; Jazouli, et al., 2019; Bachri & Shresta, 2010). AHP incorporates the multi-criteria for the risk components to develop a detailed spatial risk map. To achieve weight and rank in a multi-criteria layer, AHP uses a hierarchical structure (Roy & Blaschke, 2013).
Landslide-related studies in the southeast part of Bangladesh are mainly concentrated on the area of Bandarban and Rangamati. It does not take Ukhiya and Teknaf Upazilas into account for an extensive landslide risk assessment. Most of the studies that have been done in that area are focusing on the camps of Rohingya refugees (Ahmed, et al., 2020; Tehrani & Husken, 2019; Ahmed, et al., 2020). One more study was also conducted in Cox’s Bazar Municipality area, following the AHP method (Ahmed, 2015). The study aims to develop a risk scenario of the area integrating landslide hazard, vulnerability and exposure.
A massive influx had occurred in the south-eastern region mostly in Ukhiya and Teknaf Upazilas. As a result, a large number of forests have been degraded which accelerated many landslides conditioning factors. Because of that, there might be a devastating landslide which can result in loss of life and property on a larger scale. In this study, a variety of criteria have been used to produce the result more accurately. No other previous studies concentrated both on the host communities and refugees at the same time. Whereas most of them focused only on the refugee camps, this study assessed far beyond that. A historical landslide inventory dataset has been used, which will make the research more scientific. In addition, we have considered a wide variety of factors that give us more accurate output. So, it can be helpful for the researchers who will conduct future research in this area to identify and validate the risk zones in the host communities and the refugee camps. This study will give a clear view to the concerned authorities to take the necessary steps to mitigate the loss due to landslides.