Community Level Slope Disaster Risk Reduction Program through Multi-Scale Mapping by Mountain Ethnic Group in Northern Vietnam: Project Study by JICA/Lao Cai DARD/ITST

Abstract

Recent advances in remote sensing have been remarkable, not only in terms of technology but also in terms of operability and price. Ethnic minorities in the mountains have historically barely survived repeated disasters. As a result, they are still living in an environment with a high risk of landslide disasters. Although the economic conditions of these residents deter their efforts to find engineering solutions to mitigate potential landslide disasters, they can adequately assess the regional conditions daily. By combining their abundant but fragmental knowledge of landslide disasters with our “Site Prediction Technology of Mapping,” we are trying to develop a local community that can avoid disasters and ensures their safety.

This project focuses on mountainous areas in northern Vietnam and is a collaborative effort among Vietnamese and Japanese engineers, local governments, and international organizations. We have begun to present ALOS World 3D (AW3D) data and data acquired by Unmanned Aerial Vehicles (UAV) to residents and use them for disaster prevention and evacuation drills. This mapping process is called Communication Based Evacuation Mapping (CBEM). Despite Japan’s long history of using maps to prevent disasters, it is rare for residents to use them actively, as having an engineer make and publish a map will not lead to its use by the residents. This paper introduces a series of measures taken from the creation of maps to the engagement of residents in slope disaster risk reduction.

1 Introduction: Necessity of Mountainous Slope Disaster Prevention in Mountainous Areas of Vietnam

Vietnam is located in the northern part of Southeast Asia, on the central coastal region of the Indochina Peninsula. It is long in the north-to-south direction, from 8 degrees north latitude to 23.5 degrees north latitude. The Annan Mountains run parallel to the coast. Southern China and Laos border northwestern to the central part of the country. The border area is steep and mountainous, with an average altitude of more than 2000 m. The mountainous region has a tropical monsoon climate and is influenced by northeast trade winds and typhoons. It receives a large amount of precipitation during the rainy season, with the annual rainfall reaching 4000 mm in some areas. From the Annan Mountains, the backbone of the Indochina Peninsula, to China in the north and west to Myanmar, the geology of the Mesozoic to Paleozoic Erases is widely distributed. The Paleozoic zone suffers from large-scale fold deformation (Nam 1995). Many ethnic groups live in these mountainous areas of Vietnam. Ethnic minorities generally retain their traditional lifestyles, and many make their living by farming in mountainous areas. While income levels appear typically low, the survey sites often provide glimpses of self-sufficient living styles. Survey sites indicate that basic infrastructure, such as roads and electric power, are often inadequately developed, and the living and working conditions are poor.

In recent years, there has been concern that natural disasters caused by global warming and climate change are becoming increasingly severe, associated with heavy rainfalls, particularly in mountainous areas of Vietnam (MONRE 2021). The study areas have a long geological history of folding and faults. Moreover, chemical weathering during tropical rain has strongly affected the areas.

According to data on the risk of global disaster fatalities compiled by UNDRR (2009), South and Southeast Asia, from India and Nepal to the Philippines and Indonesia, are considered the world’s largest high-risk regions.

2 Regional Overview and Vietnam’s Disaster Prevention System

2.1 Slope Disaster Risk in Northwestern Vietnam’s Mountain Region

A sizable tectonic region (Red River Fault) runs from northwest to southeast through the central part, along which flows the Red River. The area has elevations over 1000 m above sea level, containing Phan Xi Pang (3143 m above sea level), Vietnam’s highest peak, which rises on the border of Lao Cai Province and Lai Chau Province. In these mountainous areas, unstable slopes are widespread, with active sediment movement associated with landslides and debris flows. There were 946 landslides in 15 northern provinces between 2001 and 2019, according to the Ministry of Agriculture and Rural Development (MARD) (2020). There have been 590 flash floods. These disasters resulted in the deaths of 748 residents and damaged 52,000 homes. One of the most striking aspects is that nearly 4000 houses were relocated due to the disasters.

In our preliminary survey, we noted that the mass relocation in villages was an early sign of the occurrence of landslides. Although relocations were in progress in other villages, some families reportedly returned to their old homes. Residents of North Vietnam are generally well aware of the high risk posed by landslides due to the prevalence of factors such as topography, geology, and climate conditions. It can be inferred that such awareness was a driving force behind the Vietnamese government-sponsored relocation program.

2.2 Disaster Risk Characteristics from the Humanities and Living Environment Perspectives

The area around the northern mountain provinces serves as the residence of various hill minorities. Although the life and land use tendencies of each ethnic group are diverse, the Thai, Tay, Hmong, and Dao tribes have a population greater than 1 million (Dang 2002). Generally, they make a living by cultivating rice terraces on the slopes, paddy fields, and pastoring buffaloes. Rice terraces are an excellent way to use the landscape in this area, but this requires that the natural forests be cut down. Thus, there are concerns that the risk of slope collapses and debris flows will increase during heavy rains. We believe it is necessary to understand the relationship between the risk of slope disaster occurrences and land use. However, quantitative assessments of the relationship between the two have not been examined.

2.3 Vietnamese Government’s Disaster Risk Reduction Policy and Regional Disaster Risk Reduction Policy Initiatives and Challenges

Efforts to tackle slope disasters in Vietnam began with the enactment of the Disaster Prevention Law (Vietnam’s National Assembly 2013). Tachi, a JICA expert from the Ministry of Agriculture and Rural Development (MARD), and Sakai, a JICA expert from the National Research Institute, took further steps (Tachi and Sakai 2019). Based on these references, we submitted a proposal for a slope project outlined by Disaster Risk Reduction. We will outline slope disaster prevention in particular.

Government Policy

The Disaster Prevention Law sets out five basic principles for preventing and managing natural disasters. These are: (1) In extreme weather, the Vietnamese government must make proactive plans for the prevention and timely response to take prompt and effective corrective measures. (2) The prevention and control of natural disasters is the responsibility of the State, organizations, and individuals. The State plays a leading role, organizations, and individuals take the initiative, and local communities help each other. The prevention and control of natural disasters are carried out according to four maxims on the spot: command the local army for the organization of households or individuals in an area at risk of the natural disaster/s, vehicles and materials, and onsite logistics. (3) Natural disaster prevention and management content should be integrated into national and local socio-economic development master plans. Sectoral development master plans must ensure humanity, fairness, transparency, and gender equality. (4) For to prevent and control natural disasters, actions taken by the State must be based on science. Combine traditional experiences with the progress made through science and technology. A combination of structural and non-structural solutions; environmental protection, ecosystems, and adaptation to climate change. (5) Prevention and control of natural disasters will be decentralized with close coordination between armed forces and natural disaster risk levels (National Assembly of Vietnam 2013). An organizational chart of disaster prevention measures to be constructed at the local people’s committees level is also presented. It clearly states that this mechanism assists with disaster prevention through the cooperation of each organization in the region.

Needless to say, natural disasters in Vietnam may also be related to social factors. In Southeast Asia, such as Vietnam, paddy field cultivation and slash-and-burn cultivation using slopes have been practiced since ancient times. This practice suggests that many people live on mountainous slopes, with a high possibility of landslide disasters and soil erosion due to land use. In a social environment where mountain slopes are both a place of land use and a residence, it suggests the necessity of measures to mitigate disasters (Fig. 1).

Fig. 1

Diagram shows the relationship between slope disasters, objects, and management tools. (a) Management level pyramid from National to community. (b) Disaster management tools

Especially in areas with moist tropical mountains, such as Vietnam, slope disasters are repeatedly disrupting the lives of residents. However, residents in mountainous areas lack the practical knowledge and skills to avoid disasters. Although government officials are concerned about this, adequate measures are not easy to take. Disaster prevention organizations are established at all levels, from the center to the local level, including the provincial, district, and communal levels. The ability to understand landslides at the actual administrative level varies from program to program, plan, or project. At the regional level, and in villages, it is necessary to formulate appropriate response plans, taking into account the level of knowledge related to individuals involved the disaster prevention.

We need to educate the residents to raise awareness of landslides, such as what they are, what their causes are, when they occur, and pointing out landslides and safe locations. Maintaining a map with appropriate accuracy will be necessary to satisfy the above requirements. Examples include (1) an integrated map of landslide risk assessment, (2) a landslide distribution map at an appropriate scale, and (3) a map that can help locals identify the extent of the landslide area and the features associated with the topography in the area in which they reside.

At the national level, the Ministry of Natural Resources and the Environment has prepared a slope-disaster risk assessment map at a scale of 1:50,000 for use in community-scale development (Hung et al. 2017). However, this is not easy to apply to the scale of local communities such as communes and houses. For their benefit, further creation of applicable disaster prevention maps is required.

3 Significance and Framework of the Project Outline and Aim of the Technical Support Project

3.1 Background to Building Relations and Identifying Issues Between Vietnam and Japan

In the past, the project “Development of Landslide Risk Assessment Technology along Transport Arteries in Vietnam” (Project leader: Kyoji Sassa, Academic Representative of the International Consortium on Landslide, ICL) was implemented as a project of the joint JICA/JST Planning Project (SATREPS) between 2011 and 2016 (Tien et al. 2017). As part of this project, “Extraction of Landslide Danger Slopes by Wide-Area Landslide Mapping” was established, and the authors of this paper (Miyagi, Hamasaki, DV. Tien, N.K. Thanh, etc.) are core members, leading to the cultivation of important technology, knowledge, and relationships. These elements proved to be foundational to the subsequent project. In 2017–2018, a science program was adopted as one of the JST’s Sakura Science Programs, which allowed the authors to invite young engineers from Vietnam to introduce the current situation of landslide disasters and response measures in various parts of Japan. In 2018, an international symposium entitled “The Reality of Slope Disasters Caused by Earthquakes and Ways to Overcome Them” was held in Kurihara City. This event commemorated the tenth anniversary of the Iwate Miyagi Inland Earthquake, which caused the largest known landslide in Japan, the Aratozawa Landslide. Five years later, the Kurikoma Geopark was established in the wake of the landslide disaster. Kurihara City was the proposed municipality for this project but has had a history of academic exchange between Japan and Vietnam since 2011.

This project is implemented as JICA’s grassroots technical cooperation. The project is organized into two parts. The Japanese side consists of Kurihara City as the implementing body of the proposed municipality and Advantechnology Co., Ltd., and the Vietnamese counterpart Department of Agriculture Rural and Development (DARD) of Lao Cai Province. ITST of the Ministry of Transport (MOT) is a support organization.

In 2015, the Third United Nations World Conference on Disaster Risk Reduction was held in Sendai. Here, the natural disaster response policy from 2015 to 2030 was adopted as the Sendai Framework for Disaster Risk Reduction 2015–2030 (UNDRR 2015). In 2015, the Third United Nations World Conference on Disaster Risk Reduction was held in Sendai. The natural disaster response policy from 2015 to 2030 was adopted as the Sendai Framework for Disaster Risk Reduction 2015–2030 (UNDRR 2015). Four of the seven action guidelines presented in the Sendai Framework focused on communities and residents relating to establishing early warning measures.

3.2 Outline of Technical Support Project

Based on the background described above, this project aims to expand the experience and mitigation technology in Vietnam (cultivated over more than ten years) to the residential areas of hill tribes, which are considered to be one of the most challenging areas to reach and yet the most in need of such assistance. The intention is stated in the project title, “Capacity Building of local Community for Slope Disaster Risk Reduction - SLOPE DRR.”

The overall goal of this project is for residents to work together to grasp disaster risks better and build disaster-resilient communities. The immediate goal is for residents to take the lead in formulating and implementing disaster prevention, mitigation, and evacuation plans. To that end, (1) It will be necessary to grasp the characteristics and disaster risks in the community areas. (2) On the Japanese side, administrative authorities and regional disaster prevention officials will work together to implement an awareness program focused on understanding disaster risks and evacuation. (3) Community-level organizations will formulate evacuation plans autonomously based on the materials and experience cultivated in (1) and (2). (4) Through pioneering activities, we will foster disaster avoidance capabilities in local communities. As already stated, it is challenging to establish regional disaster prevention works in which residents take the lead. However, it is also true that in recent years, the development of various notable technologies and social systems in sensing has progressed. We are consciously utilizing UAV, AW3D data, and Google Earth. In this project, as a mechanism to foster a common understanding between engineers and residents through visualization and exchange of opinions, we are using technologies such as UAVs that can easily acquire images of the region at a low cost to construct precise maps using digital information through research. With the help of UAV-related technology, it is possible to assess a site with residents immediately after a disaster. This approach may have been different in conventional disaster research and disaster prevention planning. Residents can be victims of a disaster, in essence. We feel that the use of UAVs has the potential to foster collaboration among these individuals. In addition, using AW3D can pave the way for the region and the government to understand the disaster potential by developing regional topographic landslide distribution maps. Data can be created on digital topographic maps of wide areas that can supply much useful information regarding geography and geomorphology at a much lower cost than aerial photographs and the like. The AW3D JAXA/RESTEC/NTT DATA uses four million photos acquired by the Japanese satellite Daichi. This developed technology can build Digital Surface Model (DSM) data with a 2.5 ~ 5 m resolution anywhere in the world.

In parallel with developing high-precision local land information using advanced technologies, we will conduct a questionnaire survey of residents. Although the questionnaire is simple in terms of disasters and the necessity of disaster prevention, it will be possible to grasp the level of awareness of the residents themselves and the necessity of preparing basic materials for disaster prevention in the region. Some specific questions include: (1) To what extent do you grasp the status of disasters occurring in the region? (2) How much basic knowledge do you have about disasters in general? (3) How strong is the awareness of promoting regional disaster prevention? We believe that combining the local land information and the survey results will lead to constructing a technical and organizational system that contributes to regional disaster prevention.

In this project, three communes of two districts of Sapa and Baxat Districts in Lao Cai Province have been selected as pilot communes. In these areas, we collaborate with residents and the local government to promote initiatives that contribute to mapping, regional surveys, disaster avoidance, etc. In the following section, we report on the status of initiatives in Trung Chai Commune, Sapa District, Lao Cai Province, where progress is clear at this time.

4 Various Initiatives for Mapping in Trung Chai Commune, Lao Cai Province

4.1 Hypothesis of Communication Base Evacuation/Risk Mapping

Main Premise

The importance and difficulty of regional disaster prevention is the development of an evacuation map among community residents. Disaster mitigation must formulate a disaster response map that balances disaster risk and regional safety and has been improved over and over for decades in Japan. This need is also clearly stated in the Natural Disaster Prevention Law enacted in Vietnam in 2013 (Vietnam Government 2013). The Red Dao ethnic group resides in the pilot area of the Trung Chai commune. According to interviews conducted in this study, their awareness of disaster prevention is very high (detailed interview survey in Sect. 4.5 in this paper). This study focuses on the necessity and possibility of creating a “communication-based evacuation map to realize slope disaster prevention.”

Two hypotheses have been established, as explained in the following two sections. We propose to select three local communities to serve as pilot communes. The goal is to create a more disaster-resilient commune by developing disaster prevention measures through interactive evacuation maps. Why is it necessary to “conduct two-way communication between engineers and residents and jointly create disaster prevention and evacuation maps” mentioned above?

• Hypothesis 1: Using hazard maps can reduce disasters.

In reality, hazard maps are not currently utilized by residents. There are four main reasons for the lack of utilization of such maps, the first being that residents feel there is no prospect of a disaster. Every time a disaster occurs, a common sentiment from victims is that they never thought it would happen to them. This mentality is based on their assumption that since they were not affected by previous disasters, they will remain unharmed. The second reason is that residents do not put forth the effort to use hazard maps. If a person knew to read such maps, disaster response would be fast. Another reason hazard maps are not implemented is that the responsibility is often left to a government entity. Lastly, it’s hard to predict how and where a disaster will occur, leaving evacuation maps obsolete. To summarize, reasons for hazard maps to be effectively useless are low awareness, shifting of the responsibility of implementation, the unpredictability of disasters, and a general sense of apathy.

Incompleteness Among the Hazard Map Maker

A Hazard Map Maker wants to make an advanced map. It is developed with this specific use in mind. Hazard maps are often created mainly through contracts between the government and the contractor. Inevitably, the map is made considering the administration’s thinking and budget. On the other hand, the target areas have extremely individual circumstances leaving a wide range of aspects for which the disaster prevention maps created are difficult for residents to utilize.

• Hypothesis 2: If you make it yourself, you want to use it daily.

In general, residents have a vague sense of uneasiness about the possibility of disasters in the area, whether they make a map or not. With the following factors in mind, communities can use hazard maps: (1) Give subjectivity to maps created. (2) Since the community makes this map, it is more personal and will accommodate their interests and needs. (3) Learn from examples of disasters in surrounding areas, and use that to inform how to avoid similar problems, and evacuate effectively. (4) In addition to disaster prevention, it can also be used to understand the regions’ characteristics.

Past Examples and Cartographers’ Perspectives

The above hypothesis is based on one of the authors’ experiences with the effects of tsunami evacuation plans during the Great East Japan Earthquake in 2011 (Miyagi 2016). Since 2006, the author has been engaged in initiatives to evacuate residents in the event of a tsunami in some areas of Miyagi Prefecture in Japan. The region had already anticipated a significant earthquake and tsunami during the short earthquake. To this end, we have been conducting evacuation-related field checks and making maps. This work was carried out so that “the authors and residents exchanged opinions” (Miyagi 2016). The region’s conditions, related knowledge, and information change over time. For this reason, updating the map almost every year was necessary. There were two ways to create maps: My Evacuation Map for family members to evacuate and Community Evacuation Map to manage the area. Three months after the sixth upgrade was made and the version distributed to all households, the M.9.0 East Japan Earthquake occurred, and a massive tsunami with a maximum wave height of 10 m struck the area. It was on a scale far beyond expectations.

As soon as the earthquake struck, most residents fled to evacuation sites according to plan. However, we realized that the evacuation site could not be safe. Based on the mutual agreement of the evacuees, we made a second evacuation to a higher place. As a result, the number of victims in the community that had previously prepared evacuation maps was overwhelmingly small compared to others.

Here, we realized the greatest role of hazard maps. The residents learned the importance of cultivating disaster response skills through map-making. A resident said, “The tsunami did not come as you said. But I was studying, so I was saved by the second evacuation.” To summarize this experience, the authors set the concept of cartography as follows.

“Communication Base Evacuation Mapping (CBEM)”.

Integration of hypotheses: The two hypotheses above suggest that a hazard map will more likely be used when residents make it voluntarily.

4.2 Mapping Steps

We have been working on mapping actual information in three communities to create a two-way slope disaster prevention map as a Communication Base Evacuation Map (CBEM) and figure out how to utilize it effectively. The steps for this map are as follows:

• Step 1: Development and improvement of the printing version AW3D and site map.

• Step 2: Listen to residents’ experiences of natural disasters, unwritten rules, etc.

• Step 3: Hold workshops with residents.

• Step 4: Recognize trends in spatial perception.

The above steps will be implemented for each community. By repeating these four steps, the disaster prevention capabilities of the region will gradually improve.

The target area belongs to an ethnic minority called the Red Dao. Since these people have distinct characteristics peculiar to the region (Dang 2002), discretion is necessary. As assumed here, the Dao people in the mountainous areas surveyed have yet to see an accurate map. Part of them may not speak Vietnamese. The illiteracy rate also seems to be high. On the other hand, many locals have recently mastered using smartphones despite many difficulties. With a smartphone, they can use open-source images like Google Earth. The current situation allows us to feel that there is a potential to dispel many of the concerns mentioned at the beginning of this article.

4.3 Disaster Experiences of Residents

According to statistics for the past ten years (2010 to 2020) in Lao Cai Province (Table 1), many damage cases have been recorded, including 128 deaths and missing persons, 179 injuries, and damages to 3464 houses. As shown in Table 2, 103 people were recorded dead or missing in the flash flood in 2008.

Table 1 Natural disasters result in Lao Cai Province Vietnam 2010 to 2020 (Lao Cai DARD 2021)

Table 2 Major natural disasters and the damage from 2008 to 2020 in Lao Cai Province, Vietnam (Lao Cai DARD 2021)

There are 13 provinces in the northern mountainous region, not limited to Lao Cai Province. In addition, various slope disasters and flood damage occur in the mountainous provinces of central China almost every year (Lao Cai DARD 2021).

Case Study of Slope Disaster at Trung Chai Commune

The commune is located halfway between Lao Cai City and Sapa City. The Mong Sen River flows south of the area and is paralleled by National Road 4D. The construction of expressways is currently ongoing. The Mong Sen area can be cited as a major landslide-disaster-prone area (Fig. 2). Landslides have been recorded in the Mong Sen region during heavy rains in 1998, 2002, and 2004. On May 9, 2004, a series of disasters occurred, including a large-scale landslide near the Mong Sen Bridge, frequent debris flow throughout the surrounding area, and large-scale debris flows blocking the Mong Sen River (Yem et al. 2006; Duan et al. 2011). In the region, surface landslides and debris flows have repeatedly occurred. Our visits confirmed micro features of secondary landslide deformation in Posingai and Mong Sen villages, which are part of a significant landslide topography. Many residents seem to have a grasp of where these disasters are located and the signs of disasters. They were also confirmed in a joint survey conducted by Vietnamese and Japanese engineers and residents, as shown in Fig. 6.

Fig. 2

Landslide and debris flow at Mong Sen Bridge, SaPa district Lao Cai in September 2004 (Left, Yem et al. 2006); Recent Mong Sen Aeras (Right, Thanh N.K., on March first, 2020)

4.4 Difficulty of Community Disaster Prevention

The provincial disaster prevention authorities (Lao Cai DARD), in charge of regional disaster risk management, have faced various difficulties unique to the field. According to the impression of community-level disaster prevention officers, efforts at disaster risk reduction on the community level seem to face various difficulties (Fig. 3). Specifically, more concrete measures are needed to improve the capabilities of people in charge of disaster management in a community. Experience in assessing disaster risks, the response to the risks, examples of what it means to have expertise in disaster management, and improvements to the abilities of the personnel in charge can occur immediately. Vietnam’s community disaster prevention policy was recently launched (Vietnam’s National Assembly 2013). However, organized guidelines on the importance and purpose of reducing disaster risks through the voluntary actions of residents and specific means have yet to be developed.

Fig. 3

Difficulties in disaster prevention at the community level

Each region is unique, with diverse disaster characteristics, infrastructure, and land use. Even if a national government or other super-authority sets uniform guidelines, it will be accompanied by difficulties applying them to the region mechanically. Furthermore, in the Vietnamese general society, the custom of using maps as essential information to accurately grasp the region seems limited. In addition, there are difficulties, such as not speaking Vietnamese and having a high illiteracy rate among ethnic minorities.

To summarize, the following five points should be improved. (1) Poor systematic knowledge of the disaster itself. Disaster prevention personnel at the regional level need to be equipped with the skills to assess the disasters experienced by the region and to examine the disaster prevention measures. (2) More concrete disaster prevention and disaster prevention scenarios must be implemented. Specifically, more than precipitation information that is thought to lead to the prediction of disasters is required. (3) Insufficient development of voluntary disaster prevention organizations has occurred. Organizations to tackle disaster prevention and mitigation are being developed in the region. However, the role that the members of these organizations should play needs to be clarified. In addition, the development of voluntary disaster prevention organizations with on-site response capabilities to address the issues in the individual local communities is an issue for the future. (4) More human resources are necessary. Both community and planning personnel are few. The number of trained people is further limited. (5) Extreme weather and disaster forecasting in recent years have been complex. The complexity of these projections makes the previous four efforts difficult.

4.5 Interview Survey on the Necessity of Slope DRR

Characteristics of Residents in the Pilot Interview

The interviews were conducted in Posingai Village in Trung Chai Commune and Lao Vang Village in Phin Ngan Commune, where the risk of landslide disasters is high. The inhabitants of the villages are ethnic minorities known as the “Red Dao.” They have a history of seeing natural disasters that occur in their region in a day in 2016. After several days of heavy rains, the risk of landslides and debris flows increased, they thought. In light of this situation, the residents decided to relocate to an upstream land about 1 km away. In cooperation with the local government, they moved and settled there. Residents and the local government worked together to develop various infrastructures such as the maintenance road, schools, cultural facilities, and electrical machinery. However, to maintain their daily routines, they have to continue using their original farming fields, which are susceptible to landslides and debris flows.

Perception of the Current State of Slope DRR in Local Communities

Local Communities: The interview was intended to increase the local people’s awareness about slope disasters’ impacts. This interview is believed to be a pivotal component of the direct approach to preventing slope disasters. Here, direct sensing is a technology that visually interprets land information acquired through a sensing tool. A typical example of this is aerial photo interpretation. In particular, UAVs can engage residents in work processes such as data acquisition, imaging, and three-dimensional processing. The data and interpretation results obtained in this process are expected to be independent natural sources for a common understanding. We can consider the significance of visual interpretation together with residents as highly significant. The UAV initiative is an attempt based on our hypothesis that the situation in which the residents are involved in the creation of materials will be directly linked to the revitalization of the use of data. From there, we can make an image from which it is feasible to evaluate the challenges to overcome in the short and long term and examine the feasibility of building a society that understands the most appropriate response solutions.

This study has five to six questions about the basic knowledge of slope disasters, involvement with local communities, and experience with disasters. These questions and the result are summarized in Tables 3 and 4.

Table 3 Results of the interview study related to the basic knowledge of slope disasters in the Trung Chai Commune and Phin Ngan Commune, Lao Cai Province, Vietnam

Table 4 Result of the interview study related to residents’ basic knowledge of the community in the Trung Chai Commune and Phin Ngan Commune, Lao Cai Province, Vietnam

The response from the residents in the surveys indicated a need to reduce the risk of landslide disasters. They are often direct victims of disasters. In recent years, slope disasters have occurred frequently in the pilot area from 2016 to 2020, and large-scale slope disasters occurred in 2002 and 2004. Experience history proves that disaster prevention measures alone cannot protect the local communities and people’s lives. Therefore, residents must formulate voluntary disaster mitigation measures to reduce slope disasters. To realize the residents’ understanding of regional disaster risks, we will build a communication-based disaster prevention map that residents and engineers jointly implement.

4.6 Arrangement of the Base Maps and Validity

Data Mapping in Trung Chai Commune (AW3D and Layer Structure

Contour lines generated from the AW3D 2.5 m DSM data covering the Trung Chai area can be used to understand the primary land conditions of the area. In addition, land cover, roads, and building system information could be obtained from Google Earth. This information can be superimposed on AW3D maps by simple ortho-processing (Figs. 4, 5, 6, and 7). This data will be the basis for creating a communication-based evacuation map (CBRM) that can be edited to be easy for local people to use. It is also necessary for the residents to understand the engineers’ intentions to prevent regional disasters.

Fig. 4

Series of maps of a portion of the Trung Chai Commune, Lao Cai Province, Vietnam. Based on the 2.5 m DSM, and 5 m DSM from AW3D (ALOS World 3 Digital Data: created by JAXA, RESTEC, and NTT Data). (1) Contour map at a 10 m interval. (2) Ortho-image for the section in 1. Houses, colonies, and roads are overlain to direct identify within the image. (3) Slope angle classification map created by GIS. Landslide topographic area developing the slope angle primarily between 15° and 35°. Surface failure primarily developed on 25° to 40° slopes. (4) Main scarp and the body of the landslide topographic area are marked based on visual identification. The debris flow and slope failure are also marked in blue as identified from the ortho and Google Earth images. (5) Ridge system and stream network system identified by the contour patterns. (6) Overlapping of the slope disaster results on the contour map

Fig. 5

Variety of the autochthonous rock facies compared with landslide materials at Trung Chai Commune, Lao Cai Province, Vietnam. (1) Fresh rock identified as “Granitic gneiss.” (2) Fresh hard rock facies exposed at channel and waterfall. (3) Slightly weathered rock with joint systems. (4) Deeply weathered rock mostly changed to a clayey texture with an identifiable grain pattern structure

Fig. 6

Field evidence based on the collaborative investigation with community residents at Trung Chai Commune, Lao Cai Province, Vietnam. (1) Recent overview of the Mong Seng Landslide (Taken on 28th Feb. 2022). The same landslide was mentioned in Fig. 2. (2): Vertical dislocation observed (between the two arrows) one year ago by the resident. It is located at the top of Mong Sen Landslide. (3) The large crack stretching near the step (No. 6) that is getting wider annually. We suggest placing a marker set. (4) Exposed huge boulder and accumulated at the landslide body. (5, 6, 7, 8, and 9) There are apparent differences between landslide materials and bedrock. The landslide body consists of deeply weathered clayey soil and crushed angular to subrounded gravel. Huge boulders are also present. (10) The slip surface of a part of the landslide material. The surface is about 7 cm thick and consists of clay to sandy loam with a thin foliated structure. (11) Buried wood fragments under the slip surface (No. 10) subject to C-14 dating in a laboratory. 12: A large wood stem (4 m long, 30 cm in width) is exposed nearby the images in No. 10 and 11

Fig. 7

Landslide topography and the field evidence collection sites at Trung Chai commune

To put it simply, as mentioned previously, no matter how precise a map for disaster response is created and provided, it will only be meaningful if the residents can understand and use it. More is needed to provide and visualize information. Instead, engineers will also need to deepen their understanding of the region through the exchange of opinion and be required to have the flexibility to make corrections for a more user-friendly map.

4.7 Verification of the Landslide Topographic Area Distribution Maps

In this research, contour lines are formed from AW3D DSM data acquired with a grid size of 2.5 m to 5 m as primary data for the mapping, including the landslide topography. Therefore, the accuracy of the terrain information is controlled by the grid size of the data. Also, since it is a DSM, it does not reproduce the terrain but often reproduces the surface of the vegetation cover layers. It seems unreasonable to use this as a source for topographic classification. However, if the contour line data generated from DSM is observed based on its accuracy, it is possible to grasp the topographic characteristics. From this viewpoint, reading the pattern of contour lines does not make any difference from conventional aerial photo interpretation. From the generated contour lines, it is not possible to grasp small-scale terrain features such as surface failures. On the other hand, it is possible to decipher the morphological characteristics of large-scale landslide phenomena on a spatial scale exceeding several hectares.

AW3D data is used as the source material to grasp the disaster risk in the area to prepare the landslide topographic distribution map. At the same time, we used high-resolution image information such as ortho and Google Earth images to identify superficial and small-scale disaster phenomena such as surface slope failure and debris flow. The disaster risk is obtained by superimposing both pieces of information in a particular area.

There is a slight gap in the understanding of slope disasters between the authors and the administrative authorities. It is necessary to devise ways to reconcile this understanding. Tachi and Sakai (2019) highlighted the following regarding recognizing slope disasters in Vietnam. Vietnam’s Disaster Prevention Law (2013) defines slope disasters differently from Japan. Two categories of landslides and debris flows are defined in the broad classification. “Landslides” are a combination of landslide topography and surface landslides, as depicted in this paper. On the other hand, “debris flows” collectively cover everything from surface landslides to debris flows. It is unrealistic for large-scale phenomena like landslides to be categorized together with surface landslides. In addition, categorizing debris flows and surface landslides together as debris flows is also very different from the classification used in Japan and is controversial.

Field Evidence and Mapping Validity

In this research, a distribution map of landslide topography is created using only contour information. Landslide topographic distribution maps have traditionally been created by interpreting aerial photographs. From aerial photographs, it is possible to decipher the morphological characteristics and related information such as vegetation, land use, small steps, and cracks in the ground. Aerial photo interpretation engineers have also considered this relevant information to determine the landslide terrain area. Based on this point, it was judged that when mapping using only contour lines, it would be necessary to evaluate the validity of the interpretation results through confirmation through field surveys.

We clarify the validity of landslide topographic mapping. In general, it is known that variations in landslide properties produce several characteristic shapes and material structures. Among these characteristics, the geology of the landslides, the microtopography, the sediment characteristics of the landslide body, etc., were confirmed. At the same time, on-site interviews were also conducted (Fig. 6).

Geology

The study area comprises granite gneiss of the Ordovician period of the Paleozoic Era. However, the study site is located in the humid tropics, suffers strong chemical weathering, and is expected to have significant weathering and viscous soiling. The stratigraphic phase of sediments disturbed by landslide action may be similar to that of weathered rocks. Here, to distinguish the determination of landslides from the rocks, the characteristics of the rocks were confirmed in the rock phase series from fresh rocks to strongly weathered rocks (Fig. 5). Even weathered primordial rocks often show crystalline particle structure and quartz veins. Using this as a clue, we checked to see if a landslide was deforming the mapped area.

Landslide Body Properties

The landslide body that constitutes the area for the landslide terrain differs from the rock phase of the original position described above and is composed of disturbed and crushed sediment (Figs. 6, 7, 8, 9). In rare cases, the slip surface and typical landslide sediments can also be confirmed (Figs. 6, 7, 8, 9, 10). Even today, it fluctuates slowly, and buried wood was found in the mobile body of the landslide when anchoring was installed (Figs. 6, 7, 8, 9, 10, 11, 12). The Japan Accelerator Measurement Laboratory collected and commissioned a portion of this to the C-14 date using the AMS method. An age of IAAA-212510 40,204;/−284 cal. BP. (Calendar year correction) was obtained. In addition, huge boulders with diameters exceeding several meters in many landslide areas are also noteworthy (Fig. 6). In landslide movement, thick, fragile, viscous weathered soil layers also cause fluctuations in fresh rocks and deeply weathered core stones during landslides. Megaliths that are resistant to surface erosion are selectively left.

Fig. 8

The simple mapping with UAV data (All data has been reported by Thanh et al. 2021)

Fig. 9

Landslide recognition using UAV data for Site A (Thanh et al. 2021)

Fig. 10

Landslide recognition using UAV data for Site B (Thanh et al. 2021)

Fig. 11

UAV Mapping at Site C (New Posingai Village) in March 2022 (by Thanh N.K)

Fig. 12

Explain the Slope DRR and CBEM. (1) A Lao Cai DARD officer representative presents the significance of promoting community-based disaster risk reduction (Trung Chai Commune). (2) Explain the meaning and contents of this activity (Trung Chai Commune). (3) Discussion with the village leader at Posingai (Trung Chai Commune). (4) Presentation of the significance (Thanh Binh Commune). (5) Luncheon meeting at the resident’s house (Thanh Binh Commune). (6) Explanation of a mapping sample (Phin Ngan Commune)

Microtopography Indicating Landslide Variation

Steep horseshoe-shaped slopes dominate typical landslide terrain through a distinct slope transformation line with the surrounding non-landslide slopes. This forward-expanding mobile body forms a gentle slope. If such a topographic composition can be observed at the site, it can be judged as a landslide terrain. In addition, if a small deformation such as a step or a crack can be confirmed in part of the terrain, and the deformation is harmonious with the assumed change in landslide movement, it can be judged as a sign of a landslide (Figs. 3 and 6).

Resident Information

Red Dao, whose residents live in the area, has been cultivating paddy fields for hundreds of years. The landscape of the rice terraces has cultural and tourist value. The residents have agreed to an evident division of land ownership, and once landslide features develop, they work together to address them. Therefore, the landslide movement might be remembered for several decades. For example, the Monsen landslide introduced earlier seems to have repeatedly been moving over the past few decades (Fig. 6).

Figure 7 shows the distribution of landslide topography drawn through contour interpretation, overlaid with evidence of landslide variation confirmed at the site. The distribution map of the landslide terrain drawn from the contour lines and the confirmation at the site are generally harmonious.

4.8 UAV Data Collection Study for Site Map and the Validity at Trung Chai Commune

4.8.1 Overview of UAV Data Acquisition and Mapping

Many image data sets were acquired using UAV and converted into a three-dimensional digital information model using SfM’s technique, resulting in multi-viewpoint photogrammetry. From image acquisition to generation and analysis of contour information, we worked together with residents. This collaborative work will significantly deepen the residents’ understanding of the map and give impetus to understanding disaster risks and formulating evacuation plans. The technology to visualize dimensionally is the Structure from motion (SfM) (Westby et al. 2012; Saito et al. 2018). This technology is used in various fields. Paradoxically, various small local changes can be captured by repeatedly acquiring images. At the same time, the operation skill of the UAVs will be deepened.

UAVs are capable of responding to the needs of small-scale study areas, especially within a limited budget, and are easy to use. These characteristics will be a powerful weapon to pave the way for the mitigation of slope disasters by understanding the living conditions of the residents in tropical mountainous regions, expanding disaster prevention knowledge, and understanding disaster risk.

Data Collection and Mapping by UAV in Trung Chai Commune

UAV data collection and detailed mapping have been carried out in Posingai Village, Trung Chai Commune, Sapa Town, Lao Cai Province. The first flight area of 3.6 square kilometers was flown in 2019 using DJI Phantom-4 Pro equipment. A series of photo images were analyzed automatically using Pix4D Mapper software with the output Ortho-mosaic images and DSMs. The simple map of this area is presented in Fig. 12. We worked with the residents to check and confirm the landslides and debris flows in the field. A topographic map with 5 m contours was built (Fig. 4). Landslide identification (Miyagi 2013; Hamasaki and Miyagi 2013a, 2013b) was implemented to identify and transfer an inventory map using the UAV data.

Within a 5 km long stretch of National Road No. 4 and its branch line running through the part of Posingai Village, 40 slope disasters were identified. They varied in size and type. Landslides, slope failures, debris flows, rockfalls, etc., could be identified. In addition, we also found places that showed unstable rocks.

From Fig. 12, we created a detailed site map for three places that we judged particularly noteworthy.

Site A (Monsen Landslide Site): A massive landslide hits Route 4 and has been plagued repeatedly for years.

Site B (formerly Posingai Village): Formerly the center of the village. In 2016, a large-scale debris flow occurred. In 2017, residents gave up on living in the area and relocated. Currently, only two households are in this area.

Site C (New Posingai Village Relocation Site): This is a new area for the relocation from Site B, where roads have been improved, and many houses have been relocated. This area is a district that expects to conduct evacuation drills.

This map shows the Mong Sen Area - a typical landslide with a width of 250 m and a height of 200 m. Referring to LS-MS 001, the slip surface depth is estimated to be about 10–20 m deep. The landslide body has been moved and changed into multiple landslide blocks. In pictures nos. 1, 2, 3, and 4, a field check was carried out, and the marked landslide sites were recorded in March 2022.

Figure 10 shows the details of site B, where in August 2016, a debris flow appeared on the natural slopes from the impact of typhoon No. 2. The initial appearance of gullies on the weathered granite surface of the natural slope is shown. The depth of the gullies is from 1 m to 3 m. According to the terrain’s natural Slope, the gullies gradually expanded and gathered to form a fan shape. The main scarps of debris flows are visible on the ortho-mosaic, for example, at the LF 010 location.

Recent UAV data of Site C (New Posingai Village), in March 2022

It was foggy when we flew a UAV to shoot the area, a common feature in the Sapa Lao Cai, but we could finish the flight. Using just about 20 minutes of automatic flight at an altitude of 300 m over a flight area of 400 m by 400 m, UAV imaging data at the center of Posingai village was collected. The accuracy results from quick data analyses with an average ground sampling distance (GSD) equal to 11.1 cm/pixel were carried out shortly afterward. The contour map from DSM makes it easy to recognize the slope stability. The created DSM and ortho-mosaic resolution data are useful for situations that need data quickly, such as training local people to evacuate.

5 Discussion of Map Adaptability and the Validity for Community-Level Slope DRR

5.1 Community-Level Disaster Prevention and Evacuation Map

A map identifies a study area and appropriately visualizes the facts in that range. The purpose of this study is to use maps for community-level disaster prevention. The community can be broken down into several scales. In addition, each community is unique. The following viewpoints are set: (1) A map to help residents implement the evacuation plans appropriately, and (2) A map to visualize the area’s characteristics, a place of daily use. To achieve these viewpoints, it was necessary to identify a suitable scale, the range to examine, and the methods of expression, among other factors. However, many different stakeholders are involved in a community-level disaster prevention program. There are several hierarchies, such as the ministry, which has jurisdiction over disaster prevention; the county, which oversees disaster prevention of the region; the commune, which will confront the disaster, the village, the home, and the individual. The contents represented on the maps should be decided with their needs in mind.

On the other hand, the cost of creation and technical difficulty should also be considered. In this study, the landslide map at a scale of 1/25,000 had already been developed. When the slope disaster danger at the province level and the county was depicted, an exchange of opinions was undertaken to find a suitable scale. The scale was agreed to be between 1/5000 and 1/10,000 for specific areas (ex., Trung Chai, Phin Ngan, and Thanh Binh Commune). A map of commune-level disaster management was also prepared. For these maps, we used 5 m DEM and 2.5 m DSM data from AW3D, which covers the entire world at a lower cost when compared with aerial photography. It may also target a specific village like Trung Chai and other communities. UAV data was taken and used for this section. The maps created by UAVs are named “Site maps.” For concrete mapping, it is necessary to consider the purpose and means of the stakeholders’ intentions. Here, we considered the ideal way for the appropriate maintenance of maps, mainly in Trung Chai Commune Posingai Village, where the most information was collected as an example.

5.2 Case Study of Site Mapping at Posingai Village in Trung Chai Commune

Trung Chai Commune is a county with an area of about 30 km² and consists of four villages. Therefore, we mapped about 25 km² using the AW3D as the base map (Fig. 4). Although the evacuation plan of Posingai village was made in that, Posingai village is about one-third of the area of the mapped region. The densely populated area is a much smaller part of the map. The current main settlement of the village is located on more complex mountain slopes. There is a history that all houses were consulted several years ago and moved to a place that was assumed to be safer because signs of a landslide appeared in the old village. Specifically, dozens of houses were moved to an area with several narrow ridges and valleys in about 20 ha only.

Based on the two viewpoints outlined at the beginning of this section, we proposed an effective map communicating the evacuation plan for Posingai Village. Suppose a community-based disaster management map is to be produced on a village-by-village basis. In that case, it will be necessary to show the main portions of the village and the relevant adjacent areas in one figure. On the other hand, it is necessary to understand and visualize the situation in further detail, such as areas with the population scattered in the village and places with high disaster risk. With this in mind, a photographic map was prepared based on images taken with a UAV. In addition, we tried to express the slope characteristics and locations of villages, including those relocated on a three-dimensional map, to make it easier to understand.

In this paragraph, we discuss the effectiveness of UAV-based mapping. The site map data obtained by flying a UAV has significant advantages and some limitations. There are limits to the range of maps. Suppose the area over which data is acquired is large. In that case, it will take a considerably long time and technical skills in various points of the acquisition time, data processing, and representation as figures. It becomes complicated even if corresponding figures are created. As a result, it is extremely difficult for an end user, such as the residents, to understand the map. The UAV data is a point to map the necessary range. When the community realizes the necessity by themself, sometimes the resident and the engineer call the data collection and develop the map together.

The initial site maps (acquired in 2019), which were created for Posingai Village, are a brief indication of the regional conditions immediately after the disaster that occurred in 2016. The effectiveness of the site map is further increased by combining it with photographic evidence on site. In addition, we introduced the site map acquired in March 2022. It provided the state of the whole village three years after the site map was acquired. The Structure of the village has almost become clear. Based on this map, the villager exchanges opinions on selecting evacuation sites and routes during heavy rains. A site map can show the disaster risk and strengths of each house block in a village, with a tentative name like “Disaster strengths and weaknesses around us. With this map, it might be possible to maintain a medical record to prevent disasters in each house. Figure 17 shows a possible example.

As mentioned above, creating and presenting disaster prevention maps according to the actual regional conditions on multiple scales over different ranges with accuracy and periodic improvements with the assistance of residents will lead to improvements in the effectiveness of disaster prevention.

5.3 Workshop for Creating the Communication Base Evacuation Map “CBEM”

To succeed in CBEM, a mutual understanding between the engineers and the residents is necessary. We already described the steps to develop a CBEM. Next, we will consider the actions that can be taken.

Explain the Slope DRR and CBEM

As introduced, the Vietnamese government’s policy promotes community-level disaster prevention. Therefore, the region carried out a series of activities described below. First, a person in charge of The Laocai Department of Agriculture and Rural Development (Laocai DARD) of the local government, which is the promotion base, will explain the purpose, set the goals, and points to emphasize for regional disaster prevention promotion to the management sector through the community officer. Next, we explain the importance of materializing CBEM and the associated creation procedure. The project has three pilot communes: Trung Chai, Thanh Binh, and Phin Ngan. We carried out the work in the same way in each commune, as shown in Fig. 16.

Initiate the Interest (Case study/Picture Story Show)

Residents need to understand the significance of disaster prevention and mapping to ensure that the effectiveness of community-level disaster prevention, primarily evacuation actions, can be guaranteed, as described earlier in this paper. Above all, the inhabitants of this area are ethnic minorities called the Dao people.

Various difficulties hamper community-level disaster prevention efforts. For example, in Vietnam, which is a multiethnic nation, mountain minorities do not necessarily understand Vietnamese. It is not necessarily understood that disaster prevention is accompanied by concrete action. In other words, there is currently a common sentiment that this topic is viewed and heard through public relations from the administrative authorities. However, as detailed in part 4.5, residents seem to believe that merely recognizing the need for disaster prevention is enough. Community-level disaster prevention begins when residents understand their significance and the specifics of disaster prevention and evacuation. If the residents are conscious of the significance of implementing the specifics independently, the actual prevention and evacuation may be attained. Thus, it is naturally necessary to emphasize the importance of disaster prevention and evacuation and to arouse interest. We introduced the case of Japan as an approach to attention. Next, we performed a disaster-prevention picture story show, “Kamishibai,” based on the community characteristics of the Dao people.

Base Map Present and Workshop for Developing CBEM

We explained the base maps developed using AW3D data for community-level disaster prevention management. These maps will become the materials for the foundation of CBEM. We also created a UAV-based site map. At the workshops, the district-disaster-prevention infrastructure map was introduced to the residents. Next, a map is distributed to each resident, and individual data, such as names, roads, residential zones, etc., are filled in. Through these processes, it was possible to make clear the community images and disaster risks among the residents. The maps were assumed to be the first experience for ethnic minorities in Vietnam to see detailed and systematic community-level maps. In addition, developing a map based on the actual understanding of the residents is an essential step to completing CBEM. Many community-level disaster prevention personnel and district residents participated in the workshops. There was no extreme bias in the age groups or genders of the participants. To widely grasp the ideal way of map understanding, which presents each district by changing the description items and the description range little by little, it was more rational for all stakeholders (Fig. 13).

Fig. 13

Workshop communication, explaining the Slope DRR and CBEM in Trung Chai Commune. (1) Explain the outline of the base map and related Images in the commune. (2) Explain the enlarged base map on the blackboard. (3) Group leader reports their recognition and their description to others. (4) Write while talking the knowledge through the engineer. (5, 6) Write through the advice

5.4 Data Analysis of the Spatial Cognition of the Residents

Results and Suggestions for Easy Use in the Community Through CBEM

Creating a disaster prevention map that the residents want to use is essential for disaster risk management. We applied the method of making CBEM, which Miyagi (2016) successfully implemented in Japan, to the mountainous ethnic groups in Vietnam. In CBEM, a mutual understanding was the starting point for establishing a dialogue. As a result, CBEM proposed to create a map that clearly describes the main characteristics of the region, primarily using AW3D data. The important buildings related to the social environment, especially educational facilities, and life-related information are to be shown. They include the people’s committee hall, school, hospital, and other social environments; topographical water system; disaster-related information such as landslide topography and debris flows; and life-related information such as roads and dwellings.

The Dao Ethnic Group area is too sparse to identify a specific location. The sphere of the daily life of the resident is limited to the village. Fellow villagers can identify the individuals and houses concerned. On the other hand, interest in neighboring villages was extremely scarce. It was realistic to prepare a regional disaster prevention management map based on this background. The above basic information was posted on the CBEM, but some blank items were always included in the legend for personal necessity. For adding the necessary information, the proposed regional disaster prevention management map had a column describing agreed-upon essential places in the region. They include temporary evacuation sites, evacuation facilities, expected secondary evacuation routes, individual houses, and neighbors’ homes with close relationships. By marking this while discussing with the family, the residents will be able to complete their own customized CBEM. On the other hand, more detailed map information was also required for the region.

The process of making the map called for the residents to use their experiences. To develop an easy-to-use map, it was necessary to include such information. The presentation of the photo map and the images from UAVs showing traces of past natural disasters was indispensable for regional understanding and disaster prevention. In addition, 3D information extracted from UAV photographs using Adcalc3D is also presented. Some actual residents, for example, routinely viewed open-source image data, such as Google Earth. Future developments in the residents’ understanding of open-source image data are expected (Fig. 14).

Fig. 14

UAV data of Posingai village Trung Chai Commune and 3D image extracted using ADCALC 3D

5.5 Discussion with the Residents for More Understanding of the Evacuation Drill Planning at Posingai Village, Trung Chai Commune

For the evacuation drill plans, maps usually have a suitable scale for the purpose. The mapping by AW3D was suitable the set up the general orientation of evaluation. UAV mapping was effective in direct and exact site imaging among the residents. These maps were suitable for identifying the exact locations. Residents need to recognize their homes on the series of maps.

Given our previous experiences at Posingai Village in 2021, when using UAV maps, the ability to see residents’ houses and the surrounding features was much easier. With a trial UAV map, almost every resident could confirm the location of their home and nearby features along the evacuation route. A discussion on the evacuation drill plans at Posingai Village, Trung Chai Commune, was conducted in April 2022 between us and the experienced residents of the village, the former village chief, and reputable people in the community. The steps of the discussion process are shown in Figs. 15 and 17.

Fig. 15

UAV site map after discussion with the community residents at Site C: Posingai Village, Trung Chai Commune

These figures showed the final result of the discussion. The five locations (A to E) in Fig. 16 were considered safer by the people. They decided on an evacuation shelter at a higher place deemed relatively stable. The remaining four locations are areas with high, smooth, and flat shapes and sufficiently stable to save each person. However, the areas risk isolation when debris flow and surface failure occur along the road.

Fig. 16

Modified Village SLOPE DRR Management Map based on discussion with residents and engineer

Since the date and conditions at the occurrence of a disaster can not be selected, evacuation plans should be made for multiple conditions. For example, in the case of Posingai Village, the location of the inhabitants is completely different during the daytime versus the night. The presence of elderly, disabled family members, and pregnant women also change over time. It is also necessary to develop a new system to respond to such situations and promptly advance discussions on what conditions make this district the most vulnerable to disasters. We summarized the steps of the scenario of the evacuation drill in Fig. 17.

Fig. 17

Flow chart for the discussions with residents

The most important things are evaluation meetings for the next. Assessment of safety after a landslide occurs through people’s observations of the area’s topography after the landslide. This assessment is the first step when discussing using maps and evacuation drills with residents.

5.6 The Evacuation Drill at Posingai Village, Trung Chai Commune

The evacuation drill was carried out between the people of Posingai Village in Trung Chai Commune in June 2022 and us. With nearly 100 participants, five locations assessed as safe by residents were identified for evacuation drill purposes, as discussed in part 5.5. It was raining during the evacuation drill, which is a realistic simulation condition for when a natural disaster might occur. The evacuation drill is divided into two phases. The first phase is to get the locals used to the alarm signal. When the alarm sound is triggered, people move quickly from the village hall (point O) to the elementary school area (point A) in Fig. 18. The request is that people move quickly, support volunteer forces and the elderly, and leave heavy properties such as corn bags, rice bags, etc. As a result, three minutes were required to move all people to a safe location with a travel distance of 300 m.

Fig. 18

Evacuation Drill at Posingai Village, Trung Chai Commune, Laocai Province on June 2022

The second phase of the evacuation drill is carried out when people are in their houses under the assumption that a slope disaster divides the residential areas. When the warning sounded, people from clusters of houses moved to five safe areas (A, B, C, D, and E) in Fig. 18. The head of each residential cluster was responsible for guiding people to move along the route defined on the maps. During the exercise, UAV was used to re-record the entire process. People were moved to safe areas within about five minutes.

6 Remark: How about Realizing Autonomous Disaster Risk Reduction in the Community by Aiming for a Usable Slope Disaster Prevention Map?

To reduce slope disaster risks for ethnic groups living in mountainous provinces of northern Vietnam, we prepared maps and improved them through dialogues with local organizations trying to utilize their experiences for disaster risk reduction and evacuation drills. Three pilot communes in Lao Cai Province were designated, and the implementation status of the program was reported.

In the last decade, the progress of sensing tools and technology has been remarkable. In addition, the expansion of open-source images and GIS data has also been remarkable, along with discussions on the environment and disaster prevention. This project is aimed at the living areas of mountain minority ethnic groups that are generally considered to be far from investment in technology and limited in the budget to alleviate disasters. These groups live in poverty and remote areas where infrastructure development is still inadequate and traditional lifestyle habits are present. Because of this, we thought that utilizing the latest sensing, which is now considered easy, would open the way to free efforts in regional disaster prevention. Mountain minorities do not usually speak Vietnamese. However, most residents use a smartphone. Initially, we imagined that the project would be challenging. However, in actuality, we, the engineering side, and the residents understood each other the contour lines on the map as an image, and we understood the difference between a large-scale landslide and a surface landslide. In their daily life, the residents had a rough grasp of the topography, the local space, and the risk of disasters. The mapping of regional information is now easy to understand for residents. What was once considered difficult to read and not worthwhile has now been organized into an easy-to-read map. Based on this experience, we may be able to reconsider the use of Communication Base Evacuation Mapping (CBEM).