Mapping landslide events at Cameron Highlands, Malaysia in relation to land use, rainfall and elevation using Geographical Information System

The Cameron Highlands as the name implies is subjected to high landslide vulnerability due to its geographical location in a hilly area. The principal factors contributing to the landslide events in Cameron Highlands have been identified as heavy rainfall and substantial land use changes, which include infrastructural development and agricultural practices. Thus, there is a need to map the landslide events that occurred in Cameron Highlands using Geographical Information Systems concerning rainfall, land use and elevation. The relevant data were collected from the Department of Irrigation and Drainage Malaysia, the Department of Town and Country Planning Malaysia, and the Public Works Department Malaysia. Based on the findings, with the average annual rainfall exceeding 2,687mm, massive agricultural activities on hilly terrain and infrastructure development along the main road, confirmed the occurrence of landslide events in Cameron Highlands. In addition, most of the landslide events occur at an elevation of more than 1,800m above sea level. By knowing the respective locations of previous landslide events, local authorities will be able to take earlier precautions in mitigating and planning future development related to agricultural activities and infrastructure besides providing early warning and useful information to the public at large.


Introduction
A landslide can be defined as when a mass of rock, sediment, soil, or artificial fill fails and moves because of gravity.The thin layer created by paedogenic processes that directly overlies the land surface is referred to as the soil in this context [1].The occurrence of landslides typically results in the loss of human life, damage to properties, or a combination of both [2].The excessive agriculture practices of highland regions are a prominent element that stimulates the creation of high runoff, subsequently resulting in massive soil erosion loss.As a result, it causes a degradation of the steep slopes and intensifies the occurrence of landslides [3].
Malaysia also is inevitable as landslides commonly occur in hilly and mountainous areas.Malaysia has encountered numerous moderate and severe landslide calamities, and seven cases have been recorded in the year 2022 [4].Due to its geographical location situated in a monsoonal system region, heavy rainfall averaging more than 3,000 mm annually was one of the main contributors to the landslide occurrence 1249 (2023) 012005 IOP Publishing doi:10.1088/1755-1315/1249/1/012005 2 in Malaysia [5].The Cameron Highlands region has been identified as a location with high landslide vulnerability in Malaysia, which has raised significant concerns to the Malaysian government.
The occurrence of several landslide events in Cameron Highlands since the 1980s has attracted the attention of numerous scholars who have undertaken studies on landslides in this region.The majority of prior research has indicated that the principal factor contributing to landslides in Cameron Highlands is the combination of heavy precipitation and unregulated land development [5][6][7].The occurrence of regular annual landslides compelled the residents to endure persistent discomfort.Hence, the study intended to map the landslide events in Cameron Highlands with regard to rainfall, land use and elevation in confirming these contributing factors to the landslide occurrence.The aim was to ascertain the extent and impact of these factors in causing the incidence of landslides in the region.The utilisation of maps and research outcomes enables local authorities to implement essential measures, including evacuation protocols, rescue team notifications, road closures, and the dissemination of information to the public.These steps serve to mitigate the adverse effects of landslides in the region.

Landslide in Cameron Highlands
In Malaysia, the occurrence of landslides has emerged as the second most significant natural disaster, behind the prevalence of floods.In addition to the loss of human life, landslides occurring in the region of Cameron Highlands have resulted in detrimental effects on the primary and secondary road infrastructure, hence impeding economic activity through the consequential delay in the transportation and delivery of agricultural products [8]. Figure 1 shows the scenario of landslide occurrence in Cameron Highlands.The occurrence of landslide incidents in Cameron Highlands, Malaysia has consistently raised major concerns among authorities, researchers, and locals due to their impact on human casualties and economic damages.Numerous instances of landslide occurrences have been reported in the region of Cameron Highlands over the preceding years.Table 1 shows the significant landslides occurrence in Cameron Highlands throughout the period spanning from 2016 to 2021.The annual precipitation in Cameron Highlands which is similar to other tropical mountainous areas recorded an average range of 2,500 to 3,000 millimetres per year [10].The period of highest rainfall in Cameron Highlands occurs from March to May, as well as from November to December throughout the year.The observed maximum rainfall amount within 24 hours varied between 87 and 100 millimetres.During periods of increased precipitation, numerous streams and rivers in the Cameron Highlands region recorded an increase in water levels, resulting in the inundation of adjacent areas.Additionally, the occurrence of landslides, namely debris flow, is possible along the valleys of these water bodies.The impact of high rainfall intensity on fill slopes is a significant determinant and exposure of the occurrence of erosional features such as sheet, rill, and gully erosion.During periods of instability, a significant number of both natural and man-made slopes exhibit marginal stability [11].
Inadequate control and regulation of development, particularly in the agricultural sector in highland regions, have been identified as significant factors that contribute to a high incidence of landslides in Cameron Highlands [5][6][7]12].In recent times, a total of 12 landslide occurrences have been reported in the region of Cameron Highlands [13] which transpired for two (2) hours duration characterised by heavy precipitation.The aforementioned places encompass areas near Big Red Strawberry, Strawberry Park, Boh Sungai Palas, Water Crest, Rose Valley, Taman MCA, Taman Pelangi, Ringlet, and Batu 20 in Tapah.
The prolonged precipitation which amount to 270 millimetres over fourteen days as reported by the Perak State of Public Works Department resulted in the diminished structural integrity of the hillslope situated at Section 27 of Jalan Simpang Pulai-Cameron Highlands, ultimately leading to the occurrence of a landslide event which tragically claimed two lives.Thus, the rainfall weakened the slopes leading to landslide occurrence at this stretch.Based on the landslide event series in Cameron Highlands, there is a need to conduct a study in this area for further assessment and evaluation.

Geographical Information Systems Mapping
Geographical Information Systems (GIS) are widely recognised as a highly effective tool for the integration of diverse datasets and present them as a map for any disaster events such as landslides and floods.GIS technologies also can act as a powerful tool in modelling disaster hazards for their spatial analysis and prediction.The relevant data concerning disasters can be collected, manipulated and analysed much more efficiently in GIS.For many years, GIS has been applied to help in assessing and analysing risk of the disasters.Figure 2 shows GIS usage in disaster management.
There have been many studies that use GIS to map and study disaster occurrence, especially in landslide events.For instance, [14] carried out a GIS-based study to map areas of landslide susceptibility in the Dejen District, Northwestern Ethiopia.In addition, a separate study employed a Geographical Information System (GIS) methodology to delineate the susceptibility of landslides in the Portofino promontory, a region in the Mediterranean that experiences regular occurrence of heavy precipitation, leading to the frequent event of shallow landslides [15].In other studies in China, an assessment is conducted to evaluate the susceptibility of landslides in Huangyuan County in Qinghai, China [16] by employing Geographical Information Systems (GIS) and Artificial Neural Networks (ANN).Thus, GIS shows great tools for the study to be carried out and applied in mapping the landslide events at Cameron Highlands.

Study Area
The Cameron Highlands is located in the northwestern region of the Pahang State Peninsular Malaysia, encompassing a total area of 68,156.74hectares.The research region is situated at a latitude of 4° 30' N and a longitude of 101° 28' E, with an elevation of 1,829 metres relative to mean sea level.The study area, as depicted in Figure 3, illustrates the latitude and longitude position of Cameron Highlands.
The climate of Cameron Highlands is situated at the interface of a tropical rainforest environment and a subtropical highland climate.The mean annual temperature recorded was 18°C, with 66% of the terrain exhibiting slopes greater than 20°.Agricultural practices occupy 8% of the total area, while forested areas cover approximately 86%, while residential areas account for 4% of the land, leaving the remaining portion designated for recreational purposes.The current agricultural practices have resulted in significant soil erosion and subsequently accumulates substantial sedimentation.Moreover, the region of enormous economic potential is also confronted with the perilous natural hazard of landslides.

Spatial Datasets
The study primarily used secondary data collected from several government agencies such as the Department of Irrigation and Drainage Malaysia, the Department of Agriculture Malaysia, the Department of Survey and Mapping Malaysia, and the Department of Public Works Malaysia.The principal stage in the process of landslide spatial mapping is the collection of data, including the identification and derivation of pertinent factors contributing to landslides, which are then organized in a spatial format using Geographical Information Systems (GIS).The study objectives were addressed by constructing a spatial database using GIS, incorporating three parameters namely elevation, land use, and precipitation.The database collection comprises spatial datasets in vector format that have been generated using the ArcGIS 10.5 software package.

Digital Elevation Model. The region of Cameron Highlands is encompassed by a topographical terrain characterized by elevated landforms featuring inclines exceeding 20°
[18] and it exhibits a diverse range of elevations, spanning from 200.00 to 2,069.85 meters above sea level.The data was obtained from the Department of Survey and Mapping Malaysia for the year 2020 [18].

Land Use.
Land use refers to the deliberate actions taken to oversee and alter the natural environment or undeveloped areas to create constructed planning, such as cultivated fields, grazing pastures, and human settlements.This encompasses several purposes, including military operations, recreational activities, and transportation infrastructure.The land use data pertaining to Cameron Highlands was acquired from PLANMalaysia for the year 2018 [19].In the region of Cameron Highlands, the predominant land utilization consists of forested areas, with agricultural practices such as tea cultivation, vegetable farming, and the cultivation of decorative plants serving as secondary land uses.Table 2 presents the area of land use types (in hectares) that occurred in the region of Cameron Highlands.[20].The rainfall data for the year 2020 were obtained from the Department of Irrigation and Drainage Malaysia [20].

Results and Discussions
Based on the report from the Department of Public Works Malaysia, there are 75 landslide events were recorded by the agencies [13].Table 3 shows landslide events reported in Cameron Highlands.In 2016, 20 cases of landslide were recorded in Cameron Highlands, which is the highest number of landslide occurrences between the year 2012 to 2021.On the other hand, there were no landslide cases in the year 2019.These landslide occurrences were then prepared into GIS spatial data format and overlaid with the land use, rainfall and elevation.Figure 4 shows the maps of the overlay with GIS tools.Based on the land use data, more than 89.9 per cent of the landslide events have occurred on land with agricultural activities (short-term farming and vegetables) and urban development (residential and tourism).According to the [6,7], many agricultural activities without proper irrigation water and extensive land clearing for urban development were one of the major contributors to soil erosion, which consequently weaken surface slope and lead to landslides.Besides, intense rainfall in Cameron Highlands triggered continuous soil loss which increase the chances of landslide occurrence.Based on the rainfall data, 78.5 per cent of the landslide events received more than 2,687 mm of annual rainfall, which indicates that the surface is susceptible to soil loss.Another important fact is that 84.3 per cent of landslide events primarily occurred at elevations exceeding 1,800 meters above sea level, thus this will lead to a significant landslide risk of extensive damage to the surrounding area.Whereby, the affected zone can be extended beyond a radius of 200 meters from the point of landslide occurrence.

Conclusion
In this study, maps of the landslide events overlaid with land use, rainfall and elevation using GIS tools have been presented successfully.A total of 75 landslide occurrences in Cameron Highlands acquired from the Department of Public Works Malaysia were prepared in GIS spatial format.The findings indicated that more than 89.9 per cent of the landslide events have occurred on land with agricultural activities and urbanization.Increasing agriculture-related activities and excessive land clearing for development further weaken surface slopes and lead to severe landslides.Besides, 78.5 per cent of the landslide events received more than 2,687 mm of average annual rainfall, which suggests that the area is vulnerable to soil erosion.In addition, 84.3 per cent of landslide events primarily occurred at elevations exceeding 1,800 meters above sea level, possess a high threat of huge damage to the surrounding.By knowing the respective locations of previous landslide events, local authorities will be able to take earlier precautions in planning future development related to agricultural activities and infrastructure besides informing the communities of useful mitigating measures in reducing the consequences of landslide events.

Figure 1 .
Figure 1.The scenario of landslide occurrence in Cameron Highlands[9]

Figure 4 .
Figure 4.The landslide events overlay with GIS tools in relation to (a) land use, (b) rainfall and (c) elevation

Table 2 .
Area of land use types in Cameron Highlands for the year 2018 [19] Cameron Highlands is geographically located in the monsoonal system region.Typically, the rainy season in Malaysia falls from November until March during Northeast Monsoon and from May until September during Southwest Monsoon