VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY MAI THI HUONG ASSESSING THE VULNERABILITY OF LANDSLIDES IN VU GIA RIVER BASIN USING ANALYTIC HIERARCHY PROCESS AND GEOGRAP
INTRODUCTION
The necessity of the research
Climate change is exacerbating natural disasters, leading to a rise in both their frequency and severity Events such as floods, landslides, droughts, rising sea levels, and wildfires pose significant threats to human populations, causing widespread destruction of homes, disruption of livelihoods, and resulting in billions of dollars in economic losses (Thomas, 2017; Yousuf, 2023).
Landslides are a significant natural disaster that inflicts substantial damage on both people and property, affecting not only Vietnam but also countries worldwide.
Landslides in Vietnam's Northern mountainous and Central regions are primarily triggered by heavy rainfall, leading to significant hazards From early 2023 to the end of the year, nearly 166 individuals have died or gone missing due to landslides, marking a 95% increase compared to 2022 Notable incidents include the deaths of three soldiers and one civilian at Bao Loc Pass, along with two fatalities and five injuries in Da Lat City, Lam Dong Province The economic damage from these landslides is estimated at 8,236 billion VND, which represents a 42% increase from the previous year (VDDMA, 2023).
The Analytical Hierarchical Model (AHP) is a structured decision-making technique that integrates mathematical and psychological principles to analyze complex choices It offers a systematic framework for quantifying criteria and evaluating alternative options, making it a widely recognized and effective method for vulnerability assessment AHP has been applied to assess landslide vulnerability in various regions of Vietnam, including Hue, Ha Giang, and Yen Bai provinces.
In 2021, Ngoc Tuan et al utilized AHP and Geographic Information System (GIS) methods to create a landslide susceptibility zoning map for the Bac Tra My, Nam Tra My, and Phuoc Son districts in Quang Nam province The study identified that the research area is predominantly at moderate to high risk of landslides The Vu Gia River Basin, an extensive river system in Vietnam's Central Coast region, covers around 3,400 square kilometers, with mountainous terrain constituting approximately 72% of its total area.
The mountainous topography of the Vu Gia River Basin features steep slopes and rugged terrain, resulting in a network of short, swift-flowing rivers characterized by numerous rapids and narrow channels This unique landscape supports a rich biodiversity, providing diverse habitats for various plant and animal species However, the stability and economic progress of the area are threatened by landslides and climate change, despite the basin's ecological importance and an average annual rainfall of 2000 mm that sustains its ecosystem health.
The Vu Gia River Basin experiences significant rainfall, averaging 2500 mm, due to the interplay between monsoon circulation and the hydrological system This heavy precipitation weakens the soil, increasing the risk of landslides, which are exacerbated by seasonal rains, complex geological conditions, and diverse vegetation As a result, landslides have become more severe and frequent, posing serious threats to both people and property Therefore, assessing the vulnerability to landslides in the Vu Gia River Basin is essential, and this study utilizes the AHP and GIS methods to evaluate this risk.
The research questions and hypothesis
The primary objective of this research is to identify strategies to mitigate landslide hazards in the Vu Gia river basin Through this study, we aim to address key questions related to the impact and management of these natural disasters.
- Question 1: Which areas in the Vu Gia river basin are exposed to high vulnerability of landslides?
- Question 2: What are the solutions to minimize the impact of landslide hazards in the
1.2.2 The hypothesis of the research
- Hypothesis 1: The areas exposed to high vulnerability of landslides in the Vu Gia river
3 basin are some villages as Bon Glieng, A Bung, A Dinh, Pa Non, Ch Nooc, H’Ruh, Dak Ngon, Da Trang, Thach My, Hoa,
- Hypothesis 2: Some potential solutions to minimize the impact of landslide hazards in
Vu Gia river basin are constructing systems for landslide early warning, enhancing awareness of people about landslides, carefully studying geological structure to select suitable places for road construction
Research objectives
Objective 1 Landslide vulnerability assessment using AHP and GIS in Vu Gia river basin;
Objective 2 Propose solutions to minimize the impact of landslide hazards in the Vu
Scope of the research
The research assesses the vulnerability of landslides in the study area based on data collection from 2020 to 2023 The main result is a landslide vulnerability map
The study evaluates landslide vulnerability through the integration of Analytical Hierarchy Process (AHP) and Geographic Information Systems (GIS) analysis Key indicators for this assessment include slope angles, altitude, population density, land use, lithology, soil texture, rainfall, and proximity to roads.
The Vu Gia river basin, located in Quang Nam province, Vietnam, encompasses Dong Giang, Nam Giang, Tay Giang, and Dai Loc districts This extensive river system is a significant feature of the Central Coast region and plays a crucial role in the region's substantial hydroelectric development.
Framework
Figure 1.1 outlines the framework of the research, which centers around investigating the vulnerability of landslides through five primary tasks and research methods
Figure 1.1 The framework of the research
Framework 1.1 provides a detailed explanation of the objectives, tasks, and outcomes of the research conducted to assess landslide vulnerability The research focuses on two main objectives, namely O1 and O2 The primary outcome of the study is the creation of a landslides susceptibility map in the Vu Gia river basin, which effectively illustrates the vulnerability of landslides using methodologies such as AHP and GIS To elaborate on objective O1, the research involved four key tasks These tasks included reviewing the literature and hypotheses related to landslides, examining the impact of climate change on landslides in the study area, identifying eight crucial indicators affecting landslide vulnerability, and utilizing ArcGIS software to develop and analyze the landslides susceptibility map in the Vu Gia river basin Furthermore, based on the landslides susceptibility map and the weightage assigned to various indicators, the research proposed sustainable solutions to mitigate the impact of landslide hazards in the Vu Gia river basin These solutions aim to minimize the risks associated with landslides and enhance the overall resilience of the region against such natural disasters.
Literature review
Landslides are described as a wide range of processes responsible for the downward and outward movement of slope-forming material composed of rock, soil, artificial fills or a
Landslides, which account for over 80% of global occurrences, are primarily triggered by intense and prolonged rainfall, as well as human activities such as construction, mining, and earthquakes (Gravina et al., 2017) Disaster vulnerability encompasses various social, economic, physical, and environmental factors that influence an individual or community's susceptibility to hazards (Orencio et al., 2013).
Landslides can be categorized into several distinct types, including rotational landslides, translational landslides, block slides, rockfalls, topples, debris flows, debris avalanches, earthflows, and creep Each type exhibits unique characteristics and impacts, leading to varying levels of influence on the surrounding environment (Jagodnik et al., 2019).
Landslides have significant consequences that affect both human well-being and the environment, leading to substantial economic damage by destroying vital infrastructure like roads, bridges, and buildings This destruction disrupts transportation and business activities, hampering economic growth in impacted regions Additionally, landslides can drastically change landscapes, scar scenic areas, and disrupt local ecosystems Major landslides may block rivers, forming dams that trap sediment and alter water flow patterns, which can negatively impact fish migration, damage aquatic habitats, and harm plant life in these environments (Bizimana et al., 2015).
Risk is defined as the likelihood of experiencing a loss, influenced by three key factors: hazard, vulnerability, and exposure (Crichton, 1999) Climate-related risks arise from the interplay between climate hazards—such as extreme weather events and long-term trends—and the vulnerability and exposure of both human and natural systems Additionally, changes in the climate system and socio-economic factors, including adaptation and mitigation efforts, significantly impact the levels of hazards, exposure, and vulnerability (IPCC, 2007).
Vulnerability encompasses the traits of individuals, groups, or environments that influence their risk of experiencing adverse impacts from hazardous events Key factors include Exposure, which measures the probability of being directly affected by dangers like floods or earthquakes, and Sensitivity, reflecting the extent to which individuals or communities are impacted by these hazards.
6 to which individuals or communities are susceptible to the impacts of a hazard This can vary depending on factors such as health, age, economic status, and access to resources
Lack of hazard adaptive capacity refers to the inability to anticipate, cope with, resist, or recover from hazards, often due to insufficient knowledge, skills, resources, or infrastructure This vulnerability significantly influences disaster preparation, response, and recovery, making communities more susceptible to severe damage and loss during hazardous events For instance, landslides can have catastrophic effects on individuals and their assets, with the extent of damage closely linked to the population's vulnerability By recognizing and addressing these vulnerabilities, we can enhance disaster preparedness, improve response strategies, and facilitate quicker recovery.
Landslide susceptibility indicates the probability of a landslide occurring in a particular region in the future By developing landslide susceptibility maps, we can pinpoint and delineate areas vulnerable to landslides.
Landslide vulnerability is shaped by numerous community-related factors, many of which remain underexplored in existing research This highlights the necessity for further studies to fully grasp the extent of vulnerability in different communities Consequently, future research will concentrate on assessing landslide vulnerability in residential areas and creating susceptibility maps to better inform risk management strategies.
1.6.2 Overview about assessing the landslides vulnerability in other areas all over the world and in Vietnam a) Assessing the landslides vulnerability in other area all over the world
Three main methods for assessing landslide vulnerability include the Statistical Method, which analyzes data to pinpoint at-risk areas; the Deterministic Method, which uses physical and geological models to accurately simulate landslide initiation and movement; and the Heuristic Method, which draws on expert knowledge and empirical rules to evaluate vulnerability based on factors like slope angle, land use, and rainfall patterns.
Deterministic methods assess landslide hazards using mechanical laws and include techniques such as empirical methods, kinematic methods, and various modeling approaches Key factors influencing these methods are slope geometry, discontinuity characteristics, groundwater conditions, surface drainage, precipitation, seismic activity, and human impact These factors collectively contribute to slope instability A significant advantage of deterministic methods is their independence from long-term data, relying instead on established physical laws of slope stability However, due to their need for detailed geological data, these methods are most effective for small-scale assessments, such as individual slopes (Turrini et al., 1998).
Statistical methods are crucial for assessing the likelihood of landslide events by analyzing various geoenvironmental factors such as geological formations, soil characteristics, vegetation cover, slope angles, and hydrological conditions By examining the statistical relationships between these factors and historical landslide occurrences, researchers can create predictive models that estimate the probability of future landslides in specific regions These models are essential for hazard assessment, land-use planning, and disaster preparedness, ultimately helping to reduce the risks associated with landslides Landslide susceptibility assessments typically utilize two primary statistical approaches.
Statistical analysis investigates the relationships between individual landslide occurrences and various influencing factors Multivariate statistical analysis delves into the combined effects of these factors on landslide susceptibility, taking into account their interactions (Orencio et al., 2013; Mukhiddin et al., 2019) The complexity of statistical analysis is heightened by the uneven availability of data across different regions, particularly due to difficulties in gathering comprehensive information on landslides To address this, researchers utilize various analytical equations and models, despite facing limitations in data from natural, socioeconomic, and ecological sources (Pardeshi et al., 2013; P Reichenbah et al., 2018) Consequently, data collection and thorough analysis can prove challenging in extensive studies.
8 areas like the Vu Gia river basin due to its size
The Heuristic method, particularly the Analytic Hierarchy Process (AHP), allows researchers to rank and assign weights to landslide factors based on their perceived importance This approach is more straightforward and practical compared to alternative methods (P Reichenbah et al.).
The heuristic evaluation method is favored for its simplicity, as it allows experts to assign weightings to causal factors based solely on their relative contributions, without needing historical data This approach, supported by field-derived data and the evaluator's judgment, is widely used in various multicriteria analysis methods globally, including in Vietnam Popular techniques such as TOPSIS and AHP stand out among numerous methods like F-TOPSIS, ANP, and PROMETHEE, each offering unique strengths and weaknesses in decision-making processes.
Gilan Province in Iran is prone to landslides, prompting an evaluation of landslide susceptibility maps using two methods: the Analytical Hierarchy Process (AHP) and the Receiver Operating Characteristic - Area Under the Curve (ROC/AUC) The assessment incorporates seven key indicators, including slope, lithology, land use, rainfall, and distances to faults, roads, and rivers (Bahrami et al.).
Overview on the Vu Gia river basin
Figure 1.2 Location of the study area
Vu Gia river basin is a large river system in the Central Coast region, with an area of
5,500 square km(figure 1.2) Vu Gia river basin is the most important source of water supply for the development needs of people and the economy of Quang Nam province
The Vu Gia river basin, characterized by its steep terrain, numerous rapids, and waterfalls, is situated in a region with significant rainfall, making it a prime candidate for hydropower development (People’s Committees of Quang Nam, 2020).
The province's terrain is divided into three distinct regions, with the Western Mountainous Region covering 72% of the area This region features steep landscapes, averaging 700-800 meters in altitude and slopes ranging from 25-30 degrees, with some areas reaching up to 45 degrees Centrally located, the Midland Region has an elevation of 100-200 meters and a gentler slope of 15-20 degrees, characterized by its rolling hills.
"upside-down bowl" shape Eastern Coastal and Riverside Plains feature relatively flat terrain with low topographic relief (Disaster Risk Project Management Board, 2012; People’s committees of Quang Nam, 2020) c Climate condition
The basin experiences a tropical climate with two distinct seasons: a rainy season from October to December, characterized by heavy rainfall of 2000-2500 mm, primarily concentrated from September to November, and a dry season from February to August, marked by significantly lower rainfall The rainy season, influenced by the Truong Son range, begins at the end of August and lasts until January, while the dry season sees temperatures in the plains dropping below 12°C The average annual temperature is 25.6°C, with higher temperatures during the monsoon season, and ground temperatures exceeding 30°C in summer The region enjoys over 2000 sunshine hours annually, with total heat exceeding 90,000C and annual radiation reaching 141-150 kcal/cm² Humidity remains high year-round at an average of 84%, and rainfall distribution is uneven, with mountainous areas receiving the most precipitation.
The narrow, sloping terrain of the Vu Gia river basin significantly increases the risk of flooding during the rainy season, which overlaps with the storm season This combination often leads to severe floods and landslides in the region, as noted by the People’s Committees of Quang Nam.
The Vu Gia river basin features a variety of soil textures, each with unique characteristics Predominantly, loam, which is a balanced mix of sand, silt, and clay, is found throughout the area Other notable soil types include sand clay loam, with a higher sand content; clay loam, rich in clay; and sand clay, primarily made up of sand and clay Additionally, the basin contains clay, recognized as the heaviest and most compact soil type (People’s committees of Quang Nam, 2020).
The soils in this region are underpinned by various geological formations, including colluvial, fluvial, granite, and quartzite deposits Colluvial soils are formed from weathered materials that accumulate on slopes, while fluvial soils result from river activity Granite, an igneous rock, and quartzite, a durable metamorphic rock, constitute the basin's bedrock (People’s committees of Quang Nam, 2020).
According to reports from SRCCL and SROCC, global surface temperatures have risen at an accelerated rate over the past 50 years, with a notable increase of 1.44°C from 2009 to 2018 compared to the pre-industrial era This rise is significantly higher than the 0.89°C increase in ocean surface temperatures during the same period From 2005 to 2016, global surface temperatures rose by approximately 0.87°C relative to the pre-industrial period of 1850-1900, with the rate of increase spiking to 1.06°C in the last decade Since 1975, the average rise in global surface temperatures has been around 0.15 to 0.2°C per decade, highlighting a concerning trend of accelerating temperature increases.
Over the past 13 decades, global surface temperatures have reached unprecedented highs since records began in 1850, illustrating the profound influence of human activities on the Earth's climate This alarming trend emphasizes the urgent necessity for effective mitigation and adaptation strategies to combat the escalating dangers posed by climate change, as highlighted by the IPCC's Special Report on Climate Change and Land (SRCCL).
Figure 1.3 Average temperature change in the world for the entire period 1850-2018
Figure 1.4 Changes in annual rainfall (mm) in the world from period year of 1901 to
2018 based on different data sources (CRU, GPCC, GHCN)
From 1901 to 2018, global precipitation levels have generally increased across most regions Notably, between 1980 and 2018, the patterns of rainfall exhibited more pronounced fluctuations, indicating significant trends of both increase and decrease compared to earlier periods.
The graph in Figure 1.5 depicts the changes in Vietnam's average annual temperature from 1958 to 2018, highlighting two distinct periods: 1958-1985 and 1986-2018 Over these 61 years, the average annual temperature in Vietnam rose by 0.89°C, averaging an increase of 0.15°C per decade, which is lower than the global average Notably, during the first period from 1958 to 1985, the temperature increase was minimal at just 0.15°C, averaging 0.056°C per decade In contrast, the following period from 1986 to 2018 experienced a significant rise of 0.74°C, averaging 0.22°C per decade (MNRE, 2020).
Figure 1.5 Annual temperature change from 1958 to 2019 in Vietnam
Figure 1.6 Frequency of typhoon, storm,cycone, hurricane at the period year 1990-
From 1990 to 2018, 86 powerful storms classified as level 12 or higher were recorded, averaging 2 to 3 strong storms annually These intense storms predominantly occur between August and December, with peak activity noted in September, October, and November Additionally, there has been a slight upward trend in the frequency of these storms over the years.
Between 1980 and 2018, Tra My station in Quang Nam province experienced notable fluctuations in weather patterns, characterized by an increase in extreme phenomena such as heatwaves and heavy rainfall Specifically, the number of hot days rose by 0.05 days annually, equating to 0.5 days per decade, while days of heavy rainfall demonstrated a similar upward trend of 0.05 days per year or 0.5 days per decade.
In the RCP 4.5 scenario, heat changes compared to the baseline period increase from 41.2 days at the beginning of the century to 106.9 days by the century's end Additionally, heavy rain events rise from 2.7 days initially to 4.8 days by the end of the century In the RCP 8.5 scenario, the change in heat starts at 47.9 days and escalates significantly, highlighting the growing impact of climate change over time.
By the end of the century, the duration of heavy rain events is projected to rise significantly, increasing from 16 days to 153.3 days Initially, the change in heavy rain compared to the baseline period remains stable at 2.7 days, but this figure is expected to grow to 4.7 days by mid-century and reach 5.3 days by the century's end.
According to the RCP4.5 scenario, Quang Nam province is expected to experience a temperature rise of 1.4°C by the mid-21st century, with a further increase to 1.8°C by the end of the century (2080-2099) This reflects an overall average temperature increase of 0.4°C from the mid-century to the century's end in Quang Nam province.
METHODOLOGY
Overview research process
The research employed five primary methods including Data collection (1), AHP (2), GIS (3), Community Survey Method (4) and Observation Method (5)
The creation of a landslide vulnerability map involves a systematic research process comprising four key steps: obtaining component maps, identifying influencing factors, analyzing factor weights, and generating the final map with GIS software The Analytic Hierarchy Process (AHP) is employed to prioritize these factors through expert consultation The resulting map visually represents landslide risk levels, aiding in mitigation and disaster planning Spatial data is processed using ArcGIS, while Excel is utilized to analyze expert surveys for identifying vulnerability patterns Given the impracticality of surveying the entire area for landslide points due to time and cost constraints, pinpointing vulnerable locations enhances the reliability of the mapping.
Data collection
To build the vulnerability map of landslides in the Vu Gia river basin, both secondary and primary data were collected
Digital Elevation Models (DEMs) are essential tools in Geographic Information Systems (GIS), with the SRTM DEM offering a spatial resolution of approximately 30 meters and global coverage, achieving an accuracy of less than 16 meters, as sourced from NASA's Shuttle Radar Topography Mission (SRTM) Version 3.0 (USGC, 2020) These models provide critical information on terrain elevation, enabling the creation of detailed topographic maps that illustrate contours, hills, valleys, and other geographical features Additionally, DEMs facilitate the calculation of slope angles, which are vital for studies on erosion, water flow modeling, and effective land use planning.
- Topographic maps and Land use maps: The Department of Natural Resources and
Quang Nam Province offers digital topographic and land use maps, which are crucial for effective planning and sustainable development (People’s Committees of Quang Nam, 2020) The topographic maps detail the terrain, while the land use maps illustrate current land utilization, both of which are vital for infrastructure development and promoting environmental conservation.
Hydrometeorological reports provide essential data collected from the hydrometeorological station network within the Vu Gia river basin, including key stations such as Hoi Khach, Thanh My, and Ai Nghia (Hydrometeorological station website for the Central region of Vietnam, 2020).
The report on socio-economic development offers valuable insights into the conditions of Nam Giang, Dong Giang, Tay Giang, and Dai Loc districts, as outlined by the People's Committees of Quang Nam in 2020 Focusing on population data, density, living standards, and transportation infrastructure, the study analyzes current population profiles, distribution, and overall socioeconomic well-being The findings aim to enhance decision-making and inform policy development to foster socio-economic growth in these districts.
Figure 2.2 Topographic map (A); Land Use map (B); DEMs (C);
(Source: People’s committees of Quang Nam, 2020) 2.2.2 Primary data
Primary data was gathered through interviews with professionals and residents, focusing on the correlation between the end of the Lanina phenomenon in 2022 and the onset of El Nino in 2023, which has heightened the risk of landslides due to shifting weather patterns This study examines various factors contributing to landslides, such as soil properties, extreme weather events, global warming, and anticipated increases in rainfall linked to climate change In the Vu Gia river basin, climate change and El Nino are leading to more severe weather, disasters, and droughts Rising temperatures and prolonged droughts can dry out land, weakening soil stability and increasing vulnerability to erosion and landslides during intense rainfall Additionally, human activities near main roads can exacerbate steep slopes, further increasing landslide risks To effectively mitigate these risks, collaboration between experts and the community is essential.
24 considering various climate change factors This will help implement sustainable solutions to reduce risks and ensure long-term effectiveness.
AHP - Analytic hierarchy process
The Analytic Hierarchy Process (AHP) is an effective tool for decision-making in complex scenarios, as demonstrated in this study focused on landslide susceptibility assessment Experts were consulted to identify key indicators for evaluating landslide risks, ensuring that these indicators accurately reflect the underlying factors contributing to landslides.
Step 1: Identify Alternatives and Decision Criteria
Landslide susceptibility levels can vary from low to high, determined by key decision criteria such as geology, morphology, monthly rainfall, and human activity This research employs an Analytical Hierarchy Process (AHP) analysis using eight specific indicators: lithology, soil texture, altitude, slope angles, monthly rainfall, distance to roads, land use, and population density, as referenced in studies by Barredo et al (2000), Devkota et al (2013), Bizimana et al (2015), Aafaf et al (2019), El Jazouli et al (2019), and Bahrami et al (2021) These indicators reflect the natural, economic, and social conditions of the Vu Gia river basin, while also considering the effects of climate change Selected from similar research in comparable regions, these eight primary indicators are detailed in Table 2.1.
Table 2.1.The indicators determine the vulnerability of landslides
Altitude creates diverse terrain, which influences exogenous factors such as precipitation, humidity and weathering Areas with steep terrain, such as high mountains, are susceptible to frequent landslides
Steep slopes slow down water absorption, causing water to flow faster Abrupt slope changes can lead to rapid water flow, speeding up water accumulation and shortening drainage time
Areas with nearby roads are vulnerable to landslides, particularly where slopes are steep and terrain is elevated
The texture of the soil plays a significant role in landslide susceptibility Sandy soils are more susceptible to landslides compared to clay or other soil types
Certain rock types, particularly shale and sedimentary rocks, are more susceptible to landslides In the study area, the prevalent soil and rock types are metamorphic, notably highly fractured quartz schist The weathering processes acting on these rocks weaken them, generating clay and debris that create conditions conducive to landslides.
Human activities have a profound impact on the occurrence of natural disasters, including landslides Land use practices, such as development and agricultural activities, can influence landslide vulnerability
Areas with higher monthly and annual rainfall experience increased landslide activity The amount of precipitation influences the severity and frequency of landslides
Densely populated areas witness increased levels of production and land exploitation, heightening the risk of landslides
Step 2: Scoring Indicators and determine the relative importance of the indicators
Experts assign scores from one to nine to indicators in each pair based on their importance This helps compare the significance of indicators within and across options (figure 2.3);
Figure 2.3 Scale for comparison of indicators (Sujit & Subrata, 2019)
Expert surveys and general information will determine the importance of eight indicators for Vu Gia river basin (table 2.2) The area is high-slope and mountainous,
Landslide susceptibility is significantly influenced by slope angles, with over 50% of slopes exceeding 23 degrees, and altitudes ranging from 200 to 1,500 meters above sea level The predominant soil types, red basalt and ferrite, are particularly vulnerable to landslides during heavy rainfall, where soil texture plays a more critical role than precipitation levels Constructing homes on sloped terrain without proper consideration of soil properties can destabilize slopes, and inadequate slope reinforcement measures may exacerbate the problem This concern is prevalent in mountainous regions, affecting both residential developments and infrastructure projects Additionally, agricultural and forestry practices on hillsides contribute to the increased risk of landslides, while land use itself is less impactful than the angle of the slope.
Table 2.2 Importance of the indicators
By building Matrix Normalization to determine the weight of the indicators in table 2.2
(Finding more practical formulas at Appendix 3: Weighting of indicators)
The slope angle is the primary factor affecting landslide occurrence, with steeper slopes significantly increasing the likelihood of such events Elevated terrains typically feature sharper inclines and reduced vegetation cover, further heightening the risk of landslides.
- Distance to Roads: Areas far from roads are more susceptible to landslides due to
27 limited accessibility for maintenance and monitoring
- Soil Texture: Soils with high clay content are more prone to landslides because they absorb water easily and become saturated
- Lithology: The type of rock underlying the soil can influence landslide susceptibility Hard, dense rocks are more resistant to landslides than soft, weathered rocks
Deforestation, agriculture, and urbanization significantly heighten landslide risks by stripping away vegetation and destabilizing slopes Forests, which cover over 70% of the land area and consist mainly of acacia and eucalyptus trees, play a crucial role in slope stability However, the effectiveness of these trees in preventing landslides is influenced by their density and the management practices employed.
- Rainfall: Heavy rainfall can saturate the soil and increase the pressure on slopes, leading to landslides
Population density, although not a direct cause of landslides, can increase land use pressure, contributing to landslide susceptibility The basin hosts significant ethnic minority populations with a migratory tradition, leading to uneven and unstable population distribution, which diminishes its impact on landslide risk assessment.
- Distance to Roads: Traffic routes are limited in construction and expansion due to challenging terrain and socioeconomic conditions Therefore, this factor has a lower weight
To evaluate the expert's reliability, we can utilize the Consistency Ratio (CR), which measures the consistency of the data against its randomness This ratio provides insight into the objectivity of the data, as established by Saaty (1977) and further explored by Sujit and Subrata (2019).
𝑅𝐼 {CI is the consistency index
𝑛−1 { n is number of the indicators
𝑊33 ) For each n-level comparison matrix (Saaty T L., 1977) tested and generated random matrices and calculated their average CI and called Random index – RI (table 2.4)
Table 2.3 RI value for each number of indicators n (Sujit & Subrata, 2019) n 1 2 3 4 5 6 7 8 9 10
The study evaluates eight indicators, with a Random Index (RI) of 1.4 as shown in Table 2.3 The results indicate a maximum eigenvalue (λmax) of 8.408, a consistency index (CI) of 0.058, and a consistency ratio (CR) of 0.042, which translates to a 4.16% consistency rate Since the CR value of 0.042 is less than the acceptable threshold of 0.1, the expert judgment is deemed consistent If the CR were higher, it would signal potential inconsistencies in the decision-making process, necessitating adjustments to reduce variability in the importance assigned to the indicator pairs.
GIS - The Geographic Information System
ESRI defines Geographic Information Systems (GIS) as a comprehensive system comprising computer hardware, software, geographic data, and personnel, all aimed at capturing, storing, updating, processing, analyzing, and modeling georeferenced information (ESRI, 2018) In this study, ArcGIS Vision 10.8 serves as the primary software, equipped with tools for effective data management and spatial analysis Notable analytical features include the conversion of vector data to raster through the Feature to Raster tool, the Reclassify tool for adjusting attribute values based on specific criteria, and the Euclidean distance tool for calculating distances within a raster dataset.
Figure 2.4 Feature to raster tool
Research indicates that several factors, rated from zero to four based on their impact, significantly influence landslide risk Key indicators include altitude and proximity to roads, which elevate the likelihood of landslides Additionally, soil type, land cover, rainfall, and population density play crucial roles in determining susceptibility To assess these impacts, researchers employed a decision analysis technique using ArcGIS.
30 indicators on landslides They merged weighted scores to generate a detailed map displaying areas with varying levels of landslide susceptibility
Table 2.4 Division and score the indicators of vulnerability
No Factors Value Point No Factors Value Point
Sand clay loam 3 200-500 person/km 2 1
ArcGIS software transforms raw data into thematic maps, such as those depicting roads, population density, and monthly rainfall, by utilizing processes like clipping, merging, and unioning These maps are constructed from various collected data sources To assess landslide susceptibility, multiple factors are analyzed, as illustrated in Figure 2.7 The data, derived from different sources and scales, was standardized to a 30-meter raster format to align with the DEM resolution and converted to the VN2000 coordinate system for compatibility The Analytical Hierarchy Process (AHP) method was employed to assign weights to each factor affecting landslide susceptibility.
(G) Population density (H) Distance to road
Figure 2.6 Reclassify maps of the factors
Landslide susceptibility analysis is crucial for risk assessment and mitigation planning
This study utilized eight types of maps to create a Landslide Vulnerability Index (LVI) by overlaying key indicators The LVI was calculated through a weighted linear combination method in a Geographic Information System (GIS), where weights were assigned to each indicator based on its impact on landslide occurrence The resulting LVI map highlights areas with varying levels of landslide vulnerability, from low to very high, serving as a crucial tool for identifying at-risk regions and informing mitigation strategies Additionally, the LVI map aids in land use planning and enhances emergency response efforts (Sujit & Subrata, 2019).
LVI = ∑ 𝑛 𝑛−1 𝑊𝑖 𝑥 𝑅𝑖 { i is each vulnerability factor ′ sindividual parametric map
Wi is the weight value for the individual classes
Ri is the rank value for the individual parameters
Landslide Vulnerability index in this research = "reclassify_altitude" * 0.23 +
"reclassify_slope"* 0.264+“reclassify_road"*0.020+"reclassify_soiltexture"*0.138+
"reclassify_lithology"*0.114+"reclassify_landuse"*0.088+"reclassify_rainfall"*0.113 +"reclassify_population_dansity"*0.033
According to Decision 18/2021/QD-TTg, natural disaster risk levels are categorized from one to five, each indicated by distinct colors on maps Level 1, represented by light blue, signifies very low vulnerability, while level 2 is light yellow, indicating low vulnerability Level 3 is marked in orange for moderate vulnerability, level 4 in red for high vulnerability, and level 5 in purple for very high vulnerability.
Using the methodology outlined above, the Vu Gia river basin has been stratified into five levels of landslide vulnerability:
- Very Low (index from 0.82 to 1.54, with total 117,711 pixels): Local residents should be aware of potential landslide hazards
- Low (index from 1.54 to 1.87, about 18.14 % of the area): Landslides may occur locally, particularly in areas showing signs of movement or danger (e.g., cracks, previous landslides)
- Moderate (index from 1.87 to 2.16, about 115,712 ha of the area): Widespread landslides may occur, but typically on a small scale Residents should be vigilant and remain alert in hazardous areas
- High (index from 2.16-2.44, with total 1,047 pixels): Widespread landslides may occur
33 on a large scale Monitoring and preparedness are crucial in hazardous areas
- Very High (index from 2.44 – 3 23, with 1047 pixels): Landslides are highly likely to occur on a large scale Evacuation from dangerous areas is recommended.
Community survey method
When making a landslide vulnerability map, it's important to consult local residents
Engaging the community and soliciting their feedback can significantly enhance support for your project By gathering insights on citizens' perspectives and their satisfaction with community initiatives, you can effectively tailor your efforts to meet their needs, ultimately fostering stronger backing and involvement.
Figure 2.8 The community approval survey
Researchers evaluated the accuracy of a vulnerability map in the Vu Gia river basin by soliciting feedback from surveyors regarding its clarity, predictive ability, coverage of landslide areas, and potential applicability in other regions They also collected suggestions for updating and improving the map The study employed the Slovin formula (1984) to determine the sample size, chosen for its simplicity and reliability.
General assessment of map content?
Does the forecast location match reality?
Actual landslide points compared to map
Level of application in practice and in the…
How does the map apply to other jobs?
What extent did the map fulfill your wishes?
Not good Fairly good Good Very good
Over 200 landslides were identified as vulnerable, necessitating approximately 133 community surveys based on the Slovin formula However, only eight questionnaires were collected due to survey limitations, primarily targeting Department of Resources and Environment officers involved in landslide management To enhance understanding and response efforts, it is essential to conduct additional surveys in landslide-prone areas that include local leaders and residents Increasing the number of surveys in these vulnerable regions would yield valuable insights with adequate time and resources For more details on the community surveys, please refer to Appendix 4, while the results of the expert opinion survey are available in Appendix 5.
Observation method
To create reliable landslide susceptibility maps, it is essential to validate models by comparing them to actual landslide occurrences A field survey was conducted over one day, featuring 10 randomly selected observation points along traffic routes, representing various vulnerability levels The data collected from this survey, alongside input from local residents and historical landslide information, enhanced the research findings and improved the understanding of regional risks By integrating multiple data sources, informed decisions can be made regarding mitigation strategies and disaster preparedness This study employed the RIndex method to analyze the relationship between the 10 observed landslides and the vulnerability map, utilizing this statistical tool to assess the correlation between observed landslides and predicted susceptibility levels (Devkota et al., 2013).
) 𝑥100 { ni is the number of landslides in the vulnerability class i
Ni is the number of cells occupying the same vulnerability class
The RIndex method compares observed landslides with predicted susceptibility values
In this study, RIndex validated the landslide susceptibility map, revealing that two observed landslides in Northern Tay Giang and Nam Giang districts corresponded with very high vulnerability zones Conversely, two landslides in Dai Loc district and Eastern Nam Giang district were categorized as very low vulnerability zones, despite experiencing notable erosion.
RESULTS AND DISCUSSION
Landslide susceptibility map
Table 3.1 details the weights of various indicators assessed through the Analytical Hierarchy Process (AHP) to evaluate landslide vulnerability in the Vu Gia river basin The findings reveal that slope angles significantly impact vulnerability, representing 26.4% of the total weight, while altitude closely follows at 23.0% Additionally, soil texture and lithology are crucial, contributing 13.8% and 11.4%, respectively Rainfall and land use are also vital factors, accounting for 11.3% and 8.8% of the vulnerability assessment.
In the study area, population density and distance to roads have a minimal impact on landslide vulnerability, with population density contributing only 3.3% and distance to roads 2.0% to the overall risk assessment These findings underscore the necessity of evaluating various factors when assessing landslide risk, as different indicators can significantly influence an area's overall susceptibility to this natural hazard.
Table 3.1 Weight of the indicators
Vulnerability to landslides is assessed through a detailed map that identifies areas at risk, considering factors such as altitude, slope angle, soil texture, lithology, land use, rainfall, population density, and proximity to roads This map, illustrated in Figure 3.1, highlights regions with varying levels of susceptibility, notably pinpointing high-risk areas like La Dee and Duoich commune in Nam Giang district, as well as A Nong and A Vuong commune in Tay Giang district Conversely, Dai Loc district is identified as more susceptible to land erosion rather than landslides, due to its unique physical and climatic characteristics.
Figure 3.1 Landslide susceptibility map in Vu Gia river basin
Spatial landslide vulnerability distribution
Landslides pose a significant environmental challenge within the river basin In recent
37 times, floods and heavy rainfall have become increasingly frequent and intense in the
The Vu Gia river system in Quang Nam has faced severe damage to infrastructure and property due to recent events, significantly threatening the well-being of local communities Climate change is projected to worsen these issues, with shifting temperatures and rainfall patterns leading to notable alterations in the region's climate characteristics.
The vulnerability to landslides in the Vu Gia river basin is predominantly determined by altitude (23.0%), slope angles (26.4%), soil texture (13.8%), lithology (11.4%), rainfall (11.3%), and land use (8.8%) Although population density (3.3%) and proximity to roads (2.0%) have a lesser impact, they still contribute significantly to the overall vulnerability.
Certain regions within the study area exhibit high vulnerability coupled with low population density, as shown in figure 2.7G The limited human presence in these areas likely increases their vulnerability, whereas densely populated regions often struggle with resource management and face poverty, prompting migration to seek better livelihoods Unfortunately, this migration can lead to resettlement in high-risk areas, further exacerbating vulnerability To address the risks associated with population growth in these vulnerable regions, implementing effective population control policies is crucial, particularly in Tay Giang and Dong Giang districts, where both high vulnerability and population density are evident In contrast, the Vu Gia river area is characterized by low population density, primarily due to the presence of ethnic minority groups such as Co Tu, Ca Dong, Mo Nong, Xe Dang, Cor, and Gie Trieng, who are largely migratory and engage in small to medium-scale agriculture, thereby reducing the risk of severe landslides.
The Tay Giang and Dong Giang districts in the Vu Gia River Basin have high slope angles, altitude, and rainfall (figures 2.7A and 2.7B) These factors contribute to their
38 high vulnerability to landslides In contrast, the Dai Loc and Nam Giang districts have relatively lower vulnerability due to their lower rainfall (figure 2.7F)
The Vu Gia River Basin features varying elevations, with the Western and Southwestern regions ranging from 1,000 to 2,000 meters, characterized by steep slopes of 37 to 90 degrees, increasing landslide risks In contrast, the river and stream areas, with elevations of 0-200 meters and gentle slopes of 0-23 degrees, are less prone to landslides Tay Giang and Dong Giang districts exhibit high vulnerability due to their steep slopes and heavy rainfall, while Dai Loc district is less vulnerable owing to its flatter terrain and reduced rainfall Understanding the vulnerability of each district is essential for developing effective landslide mitigation strategies to safeguard lives and infrastructure.
Fluctuating temperatures significantly alter soil texture, destabilizing structures and increasing the risk of landslides Land use practices play a dual role in this context; while afforestation and effective surface cover can mitigate landslide risks, activities like deforestation for shifting cultivation and hydropower construction exacerbate the problem Highways 14B, 14, and 64, characterized by soft and spongy soil structures on steep slopes, are particularly prone to landslides, which can lead to severe traffic congestion over several kilometers.
According to Figure 3.1, Dong Giang district exhibits a high vulnerability to landslides, particularly in the communes of Ta Lu, Song Kon, A Ting, and Xa Ba Similarly, Nam Giang district is also prone to landslides, with high-risk areas identified in Xa Zuoich, Ca Dy, La Ee, and La Dee communes, as well as A Nong, A Dang, and A Vuong.
Tay Giang district experiences a significant risk of landslides, with areas classified as having high to very high vulnerability In contrast, Dai Loc district predominantly features low to moderate landslide vulnerability due to its river-covered landscape, particularly along river areas The western and northwestern regions of Tay Giang, along with the northern parts of Dong Giang, exhibit heightened landslide susceptibility.
West of Nam Giang The Large area of Nam Giang district (over 80%) has moderate and low-vulnerability of landslides
Table 3.2 reveals that 38.26% of the province, equivalent to 1,273.3 hectares, is classified as having high to very high landslide vulnerability, with the very high category making up 10.47% or 348.41 hectares The Tay Giang and Nam Giang districts exhibit the highest concentration of landslide vulnerability, while Dai Loc district shows a significantly lower percentage of high and very high vulnerability levels.
No Vulnerability class LVI Number cells Area (ha) Area (%)
The study indicates that 85.9% of vulnerability to landslides in the Dong Giang, Nam Giang, and Tay Giang districts is attributed to factors such as altitude, slope angles, rainfall, soil texture, lithology, and poor land management These districts show a significantly higher susceptibility to landslides, primarily triggered by rainfall, which accounts for over 70% of damages in the Vu Gia River Basin Implementing effective rainfall harvesting practices could significantly reduce runoff and mitigate the risk of landslides in these vulnerable areas.
Thus, based on the landslide vulnerability map (figure 3.1) and figure 3.2, nearly a third
Approximately 40% of the area is classified as moderately vulnerable to landslides, with 34.76% exhibiting high to very high vulnerability Given the alarming impacts of climate change, it is essential to implement effective prevention measures and countermeasures to mitigate the risks associated with landslides.
Figure 3.2 Percentage of landslides per vulnerability lass
Validate the landslides vulnerability map
Due to constraints in time and resources, the research was limited to a single field survey conducted at the beginning of 2023 The survey consisted of 10 observation points:
A survey site was identified in a region with a significant landslide vulnerability of 10.47%, located on Road 1 near Agrong village in A Tieng commune, Tay Giang district This site was chosen for its closeness to residential areas, highlighting the potential risks to the local community.
A survey point was established in Pa Rong village, Ta Bhing commune, Nam Giang district, located in regions that account for 27.79% of the total area with a high vulnerability to landslides This selection was made to analyze the characteristics of areas at increased risk of landslides for a thorough assessment.
Very low Low Moderate High Very high
PERCENTAGE OF LANDSLIDES PER VULNERABILITY CLASS
Around 34.76% of the land identified as having moderate landslide vulnerability was analyzed by selecting six strategic points along National Routes 14 and 14G, Asian Highway 17, and CT02, ensuring a representative sample of these moderately risky areas.
A survey point was established at Ha Tan Pagoda in Dai Phu village, Dai Nghia Dai Loc commune, representing the 18.14% of the area categorized as low vulnerability This selection highlights the importance of incorporating diverse locations with different levels of landslide susceptibility into the research.
In the region with minimal landslide vulnerability, representing 8.84% of the area, a survey point was established at Thach My Pagoda in Thach My Town, Nam Giang District This choice emphasizes the necessity of evaluating even the least vulnerable areas to achieve a thorough assessment of landslide risks across various zones.
Very high landslide point High landslide point Low landslide point
Figure 3.3 The landslide vulnerability observation points (source: Google earth)
Vulnerable zones, which account for 70% of the total area at risk, confirm the accuracy of the initial vulnerability assessment and the reliability of identifying high-risk areas Landslides present a significant threat to human life, property, and the environment, leading to considerable loss and damage in these regions Historical data indicates that lives and property are increasingly at risk during landslide events Therefore, implementing early mitigation measures is crucial to reduce vulnerability, safeguard lives and property, and protect the natural resources vital to the community.
Figure 3.4 The landslide vulnerability observed map in Vu Gia river basin
According to the Integrated Natural Disaster Risk Management Plan of Quang Nam province, issued by the People's Committee, and the 2023 statistical report on landslides, Quang Nam faced severe flash floods and landslides in October 2023, leading to numerous tragic fatalities Experts emphasize that while these disasters may begin on a small scale, their impacts are profoundly destructive Notably, Table 3.3 indicates over 200 landslide sites in the Vu Gia river basin, with specific locations documented.
Table 3.3 Number of landslide points in Vu Gia river basin (People’s committees of
District Total Number of landslides
Small Medium Big Very big
- In Dong Giang district, there are four big landslides points such as residential area in Bon Glieng village, Ca Dang commune; residential area in two villages, three villages,
Ba commune; residential area in A Bung village, A Dinh village, A Rooi commune; Residential area in A Giang village, Den village, Ma Cooih commune
Tay Giang district is experiencing significant geological instability, with six major landslide points identified These include the residential areas of Pa Non village, Ch Nooc village, Tung, Z’Ruoc, H’Ruh village, and Ch’Om commune Additionally, the road connecting Ch’Om commune to A Xan commune and the residential areas in A Tieng commune, Buop village, R’Bhuop, and A Roh are also affected by these landslides.
1, A Rau, Ta Ri village, Lang commune
- In Nam Giang district, there are 12 big and medium landslides points such as Con Zot
In the La Ee commune, notable locations include A Son and Dak Ngon villages, alongside residential areas near the Cha Buong River and Dac Pre The Ta Pot village in Dac Pring commune and K’Rung in Ca Dy commune are also significant, as well as the vicinity of the Go Man River and Dak Dong River Additionally, the residential areas in Pa Dhi, Pa Rum B, and Zuoih commune, along with the road near the Song Bung hydropower plant, are important In Thach My town, key areas include Da Trang, Thach My 2, and Hoa Village, while the residential neighborhoods in Pa La, Ka Dang, and Pa Jing are also noteworthy.
The vulnerability to landslides can differ greatly within the same region, influenced by a range of varying factors.
A landslide vulnerability map was developed and validated using observed landslide data, confirming that highly vulnerable areas corresponded with actual landslide occurrences This validation supports the effectiveness of the Analytical Hierarchy Process (AHP) model used to assess and rank factors influencing landslide risk The map serves as a critical tool for identifying regions requiring immediate attention, enabling policymakers and disaster management agencies to prioritize resources effectively A survey conducted with local officials and residents revealed that 75% of respondents felt the map accurately depicted local landslide risks, while also indicating a demand for more detailed commune-level information and a reduction in the map scale from 1:100,000 for improved readability and application.
Proposal of the solutions
The landslide vulnerability map is divided into five color levels, each corresponding to a specific level of landslide susceptibility
- Very Low Vulnerability: These areas are generally safe for habitation
- Low Vulnerability: These areas have a low risk of landslides, but caution should be exercised during heavy rainfall
- Moderate Vulnerability: These areas have a moderate risk of landslides, and residents should be aware of the potential hazard
- High Vulnerability: These areas have a high risk of landslides, and residents should be prepared to evacuate in the event of a warning
- Very High Vulnerability: These areas have a very high risk of landslides, and residents should be immediately evacuated if there is any indication of a landslide
In Dong Giang district, the following communes have areas classified as high or very
In the Nam Giang district, several communes exhibit a high vulnerability to landslides, including Xa Zuoich, Ca Dy, La Ee, and La Dee Additionally, the Tay Giang district is home to A Nong, A Dang, A Vuong, and A Tieng communes, which are also classified as having significant landslide risks.
For areas classified as high or very high vulnerability, local authorities should implement the following actions:
- Establish comprehensive warning plans to alert residents of potential landslides
- Evacuate residents from danger zones before a landslide occurs
- Limit or prohibit development in high-risk areas
- Construct protective structures, such as retaining walls and drainage systems, to mitigate landslide risk
In addition to the actions listed above, the following measures are also recommended to reduce landslide risk:
- Educate residents about landslide hazards and safety measures
- Train emergency response teams to handle landslides and assist affected communities
- Monitor landslide-prone areas for signs of movement or instability
- Install early warning systems to alert residents of impending landslides
Landslide vulnerability maps are essential tools for local communities and decision-makers, as they pinpoint areas at risk and enhance land-use planning and zoning efforts These maps play a crucial role in disaster preparedness and evacuation strategies, while also educating residents about potential landslide hazards By promoting awareness and encouraging safety measures, they significantly reduce the risk of loss of life and property due to landslides.
An analysis of indicators influencing landslides in the Vu Gia river area reveals that slope weight is the primary risk factor To mitigate this risk, effective construction techniques can be implemented One approach involves building embankments with stones or rocks to stabilize slopes and prevent landslides Additionally, utilizing concrete or crank grid embankments offers enhanced support and reinforcement, further reducing the likelihood of slope failures.
Altitude plays a crucial role in landslide prevention, and by lowering terrain height and creating stable areas, the risk of landslides can be minimized Effective land use planning is essential, with afforestation on slopes being a key strategy Forest cover helps bind the soil, mitigating erosion and preventing washouts during heavy rainfall By adopting these measures and thoroughly addressing the factors that lead to landslides, the risk of catastrophic events in the Vu Gia river area can be significantly reduced.
Flash floods can trigger landslides, posing significant risks to communities To effectively mitigate these dangers, it's crucial to install warning systems and landslide monitoring stations in high-risk areas, particularly where populations reside and critical infrastructure, such as schools, main roads, factories, and hydroelectric dams, is located.
Landslides often happen in localized regions, particularly on mountain slopes, making these areas unsuitable for system installations, which can hinder their efficiency.
Surveying and conducting geological investigations in areas prone to landslides are essential for creating accurate landslide maps These maps enable predictions of future landslide occurrences, allowing for proactive measures and timely responses to mitigate risks.
Relocate people to avoid areas prone to landslides, to avoid economic and human losses;
To mitigate the risks associated with landslides, it is crucial to avoid constructing homes near mountainsides and cliffs, and to stay clear of drainage areas where water flow can exacerbate landslide conditions Community awareness is essential; therefore, actively educating and reminding residents about the signs of potential landslides is important Additionally, developing effective relocation plans during storms and establishing appropriate strategies for vulnerable areas can ensure prompt remediation and enhance safety.
Proposals to create or update master plans for land use, technical and social infrastructure planning related to climate change and impacts of natural disasters
To mitigate the impact of landslides, it is essential to implement strategic plans that include avoiding construction in high-risk areas such as schools, transportation structures, and residential zones Effective land-use planning should prioritize safe human settlements and incorporate reforestation solutions Additionally, providing financial and technical assistance to displaced households is crucial for fostering resilience in vulnerable communities.