Keywords

1 Introduction

India has been adversely affected by frequent, sudden, swift and widespread landslides in the hilly terrains of the country. Landslides occur as primary hazards due to high intensity or prolonged low intensity rainfall, toe erosion by the rivers, anthropogenic interventions like construction, explosion, mining and so on. The landslides have also been witnessed as secondary hazards due to earthquakes, flash floods, forest fires, glacial lake outburst floods, dam burst/breaching and so on. Geological Survey of India (GSI), Ministry of Mines, Government of India, is the nodal agency for landslides studies and management in the country. It has carried out landslides mapping in 1:50,000 scale as part of its initiatives under National Landslides Susceptibility Mapping in the affected areas. According to Geological Survey of India (please refer to Fig. 1), about 12.6% (0.42 million km2) of the country’s land territory is affected by landslides to varying extents (National Disaster Management Guidelines 2009). The landslides data collected during the mapping has an inventory of approximately 70,000 landslide events at present, spread across more than 65,000 villages of about 19 states and union territories. However, this data is still not complete and need more efforts to incorporate all existing and past landslides.

Fig. 1
figure 1

(Source Geological Survey of India)

National landslide susceptibility mapping

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The landslide susceptibility maps are also indicative of the potential landslide zones as well. The areas have been divided into different zones according to the propensity of the landslide disaster. Efforts are also being made to create maps that offer even greater accuracy in high hazard areas. The maps, however, need to be localized to give a more magnified view of the locality to be more useful. This would help building plans and local construction activities. “These maps at 1:50,000 scale can be used to regulate land use in hilly/mountainous areas. For instance, areas with higher landslide probability can be spared big infrastructure”.

In the present study, the author has made an attempt to segregate the data and information related to socio-economically and environmentally significant landslides within the country from the year 1867 to 2021. But there is a limitation in the study as such data is not well recorded and lacks any systematic formatted structured information due to ad-hoc casual piece-meal approach in the past, except in few events where detailed studies have been carried out by relevant scientific or academic organizations.

2 Terminology for Defining Socio-economically and Environmentally Significant Landslides

The term socio-economic comprises the two words “socio” and “economics”. The consequences of any landslide event which either causes death/injury of human life, homeless people, the population affected, livestock, disrupts/changes in the pattern of livelihood like a way of people living, working, and spending their time, cultural ethics and social networks of the affected families can be classified as a “Social Impact”.

The majority of incidents of serious injuries and deaths occur during the event (disaster) only, while disease outbreaks and food shortages often occur much later, depending on the nature and duration of the disaster.

Other than killing the people and animals (both livestock and wildlife), landslides destroy or damage residential and industrial development as well as agriculture and negatively affect water quality in forest land and rivers and streams.

In addition, the “Economic Effects” of the occurrence of a landslide disaster can be described as direct and indirect losses.

According to the United Nations Office for Disaster Risk Reduction (UNISDR): “Direct losses refer to damage to human lives, buildings, infrastructure, and natural resources. Indirect disaster losses are declines in output or revenue, as a consequence of direct losses or owing to impacts on a supply chain”.

Direct Losses are the most visible consequences of landslides. They may be comparatively easy to measure but they are not always the most significant outcome. They are caused by the immediate damage done to humans, resources, and the environment. On the other hand, the indirect losses rise mainly through the second-order consequences of landslides, such as disruption of economic and social activities in a community or onset of ill-health amongst disaster victims. These effects often outlast those of direct losses by months or even years and can be highly intangible. Generally, indirect costs can exceed direct costs, unfortunately, the former is difficult to assess, and thus are often overlooked or, when estimated, are too conservative.

Although most of the physical, environmental and economic impacts are noticeable, damages caused through physical destruction can be assessed in monetary terms. But the assessment of social impact is a comparatively difficult task because some of the losses are invisible. Thus, despite the absence of serious injuries and fatalities, landslides can also be recognized in terms of the significant landslides concerning their impact on the socio-economic elements.

The determination of the cost of individual and small landslides is often possible but the total cost of landslides of large geographic bodies is usually very difficult to obtain. There seems to be a clear lack of a landslide catalog database in terms of socio-economic importance in India. In this context, evaluation methodology needs to be defined.

The environmental impact of landslides are often evaluated in terms of damage and loss to biodiversity and ecosystem. Damage and loss of land is one of the most commonly affected natural element affected in every landslide and is often measures in terms of the area affected. However, in the present approach, the environmental impacts have been considered primarily in terms of loss of trees that have been damaged or uprooted by the landslide.

The author has attempted to define and classify socio-economic and environmental criteria as shown in Table 1 on significant landslides in India. The Socio-economic and environmentally significant landslides are classified broadly into three categories i.e., Low, Moderate, and High based on the range of the socio-economic and environmental damages incurred. The color codes normally used for low, moderate and high socio-economic and environmental significance are green, orange and red colors.

Table 1 Criteria for classifying socio-economically and environmentally significant landslides in India
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As the landslide data from different sources did not have any proper or pre-formatted structure, the author devised a new structured format for gathering the relevant data and information for the purpose of the present study.

3 Data Analysis and Criteria for Categorization

Extreme landslide events are frequent and sudden which directly or indirectly cause huge loss of human life, livestock, destruction of property, financial resources in a cumulative manner. However, landslide events can have significant socio-economic and environmental impacts even in the absence of fatalities and serious injuries. This paper discusses landslides in the context of the perspectives on socio-economic and environmentally significant landslides. It presents the criteria for defining socio-economic significant landslides in India, and finally summarizes 412 significant landslide incidences with respect to the above-said point of view. The present work will not be exhaustive, but will provide a criteria for classifying landslides on the basis of information on their socio-economic and environmental impacts. The said data has been gathered from the various sources including Geological Survey of India reports and Geology and Mines Department from the States, State Emergency Operations Centres, records of Revenue and Disaster Management Departments in hill states, Border Roads Organization, Public Works Department, Soil and Water Conservation Department, Irrigation and Flood Control Department, Disaster Management Authority, Planning Department, Statistics, Space Application Centre, Media Reports and News Archives, Research Publications of Universities and Research Organizations etc. The author has tried to compile relevant data on landslide disasters from the year 1868 to 2022 from all the above information/data sources.

Landslides can be caused by either natural processes or anthropogenic activity, but their socioeconomic significance is usually the result of the human-landslide interface. Landslides are usually not isolated from other natural hazards, such as excessive rainfall, earthquakes, floods and avalanches, leading to underestimation of the socio-economic and environmental impact of landslides. This underestimation is one factor in reducing the awareness and concern of both the authorities and the general public about landslide risk.

The socio-economic significance of landslides in India is a function of the country’s unique geographical landscape in terms of geology, lithology, rainfall distribution, land use/land cover, soil properties, and road and stream networks.

It’s impossible to achieve a complete accounting of the significance of landslides. Direct costs are often imprecisely recorded. However, there is ample notable research’s that attempts to study and characterize the landslide but none of the literature discusses the criteria for classifying the socio-economic impact of landslide hazard. Landslides are one of the most widespread hazards on Earth and cause thousands of deaths and injuries and billions of dollars in damage worldwide each year. Statistics from The Centre for Research on the Epidemiology of Disasters (CRED, http://www.cred.be/) show that landslides contribute to about 17% of the fatalities due to natural hazards.

During the 2004–16 period, one of the most affected countries by human-triggered fatal landslides was India. After analysis of approximately 5041 fatal landslides worldwide, from 829 landslides, India registered around 10,900 deaths, which made up 18% of the total global casualties. 28% of construction-triggered landslide events were reported for India, followed by China (9%), and Pakistan (6%), whereas rainfall accounted for 16% of the total landslides and mining for 12% in India, followed by Indonesia (11.7%) and China (10%).

The subsequent sections highlight the perspectives and criteria for defining socio-economic and environmentally significant landslides in India along with a brief discussion on the history of past landslides and their impact. However, in the present study the information related to socio-economic significant landslides have been confined to those events where either human life is lost or affected either in terms of injury, homelessness, evacuation, damage to their habitant and many more. This also includes some cases of landslides on highways where traffic connectivity was affected. The metadata of 412 significant landslides has been collected from various sources (Surya et al. 2022).

4 Discussions and Conclusions

Out of 412 landslides, 179 landslides have been classified as of low socio-economic impact, 91 as moderate and 141 as high impact landslides (please refer to Table 2).

Table 2 Number of landslides in different categories of socio-economically and environmentally significant landslides
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In order to understand the nature of socio-economically and environmentally significant events along with their impacts, the data listed above (Table 1) are spatially and temporally analyzed.

Apart from the fatalities as mentioned above, many incidences either resulted in economic loss or a combination of both socio and economic loss. As per the published report by National Crime Records Bureau on accidental deaths and suicides in 2019, 264 persons died in landslides. Over 65% of these fatalities happened in the Himalayas and the Western Ghats.

To the end, it can be said that the Western Himalaya, which includes the regions of Kumaun, Garhwal, Himachal, Jammu and Kashmir and the Northwest Himalaya is more prone to fatal landslides and higher human casualties followed by East and Northeast India which is followed by the South India including Maharashtra. The significant socio-economic and environmental effects of landslides in India will continue, as they do elsewhere in the world. In India, landslides disrupt lives, injure people, livelihoods, roads, natural resources, power, energy and communication infrastructure. This paper documented a few significant landslides from the year 1868 to 2022, which are estimated to have resulted in direct and indirect costs, killed many individuals, and destroyed or buried homes, roads and highways, bridges, rivers, pipelines and other infrastructure vital to the well-being of the affected population. But it should be kept in mind that the landslide data presented and discussed in this paper is neither complete nor fully authentic.

Damaging landslides occur where the natural landscape intersects a socio-economic landscape, and most historical landslides of significance have occurred at the human-landslide interface. However, as people continue to expand settlement into less stable areas, one need to be ever more cognizant of the landscape in which one live, and carefully manage our exposure to unnecessary risks that threaten the livelihood, lives, and the infrastructure.

5 Key Lessons Learned

The following key lessons have been learned from the brief study of 412 socio-economically and environmentally significant landslides in India.

  • Traditional investigation and remediation works may not be able to control complex chronic landslides.

  • The threshold of movements, movement rates, piezometric pressures, ground subsidence and heaves etc., need to be fixed in relation to the mode of failure and elements at risk.

  • It is not enough to predict potential landslide susceptibility spatially but also assess the run-out distance, spread and damage potential of the expected landslides.

  • Landslides hotspots must be identified and inventions prioritized.

  • Drastic changes in the river water levels must be timely informed to concerned authorities and communities.

  • Thunderous sound of rolling boulders along with dust storm have often been observed during falls and slides.

  • Landslides can lead to blockade of river or its tributary, thereby forming temporary lakes/dams. Bursting of such lakes and transitory dams may cause flash floods and debris flows in the downstream areas and result in destruction and devastation.

  • Population pressure has perhaps compelled masses to undertake cultivation on slopes that are otherwise considered unfit for such an activity. There may be a need to devise alternate or new agricultural practices to reduce slope stability risks.

  • Selection of proper grazing sites, particularly in eco-fragile and sensitive zones, to reduce soil erosion, water seepages and landsides.

  • Disaster Impact Assessment besides the Environmental Impact Assessment, should be made mandatory for all projects in ecologically sensitive unstable slope areas.

  • In the Himalayan region, most of the landslide prone areas fall in seismic zone V and IV, that also receive heavy precipitation and high intensity rainfalls.

  • Stability evaluation of debris/waste dumps and provisions for adequate drainage measures. Suitable precautionary, preventive and protection measures should be taken up to stabilize the unstable slope mass.

  • Development activities should be executed only after the detailed investigation by specialists.

  • Mushrooming of shops and buildings close to roadsides near river or tributaries, could be threatening.

  • A dense network of rain measuring stations should be installed, particularly in areas with known history of cloudbursts and landslides. Dissemination of rain data along with landslide warning, may be disseminated to people living in high risk prone areas.

  • Better weather forecasts are the need of the hour. Prepared for climate change.

  • Risk informed building codes are imperative. Information related to landslides should be disseminated to every person in the households and made available to the public in a form that is accessible to all and understood by everyone. Anyone, who is planning to buy plot or building house or hotel, should consult large scale hazard zonation maps.

  • Every stratum of society should have basic understanding and should undergo a basic curriculum for civil defence, first aid and response to landslide.

  • Power supply gets disrupted, following continuous torrential rains along with thunder storms and lightning.

  • Process of exhuming bodies from the landslide debris is mostly manual.

  • Unscientific and unplanned Quarrying, mining, use of explosives, deforestation, desiltation in landslide prone areas, can lead to landslides.

  • Wire created retaining walls or concrete slabs to prevent toe erosion or cutting by the river.

  • Educational buildings must be carefully located to avoid landslide impacts.

  • Encroachment over river channels and steep unstable slopes may be removed through a legal framework.

  • Curriculum on DRR, mock drills for safety, network schools to share experiences and resolve challenges for landslides RR&R. Remnant risks must be mapped and monitored at the community/school levels.

  • Appropriate legislative interventions desired.

  • UAVs (Unmanned Aerial Vehicles) may be deployed for observation, mapping and monitoring, particularly in the inaccessible areas.

  • A mechanism to alert and evacuate local communities at short notice through early warning systems. Sometimes, the instruments are vandalized by the local people.

  • The existing emergency communication system must be reviewed regularly to ensure last mile connectivity during disasters.

  • Recommend development of landuse zoning regulations in the landslide prone areas. Tourism related development should not be allowed along the vulnerable river banks.

  • Community based disaster risk management at the local levels must be given utmost importance and strengthened through capacity enhancement programmes.

  • Incident Response System may be established and dovetailed into the disaster management plans.

  • The aspects of psycho-social support should be integrated into medical plans for disaster affected population.

  • Waste water from hotels and local inhabitants being released into the slopes, should be diverted through lined drainage channels. Temporary phreatic surfaces within the debris, overburden and unsupported slopes, causing slope instability and eventually landslides, should be regulated and controlled.

  • Drainage in the uphill area of the landslide should be channelized and diverted away from the slide to prevent water infiltration and rise in pore water pressure of slope mass. All drainage courses need to be kept clear of the runoff debris to enable smooth channelized flow of water.

  • Precarious boulders above the crest and on the body of the slide, should be carefully removed. Immediate filling of tension cracks with suitable impervious materials on the top and permeable materials underground using appropriate techniques must be carried out to avoid infiltration of water and building up of pore water pressure within the slope mass.

  • Incorporate lessons learned from the past events into future planning, policies, strategies and actions. Analyse past experiences to know what went well and what went wrong and what could have been done better for risk reduction and emergency response. Document these lessons annually after every disaster.

  • Develop a minimum inventory list of instruments, sensors and field observation checklists required to understand the efficacy of remedial works in order to achieve the desired performance standards and develop an appropriate plan to monitor it regularly or periodically.

  • Create a mechanism for regular inspection and maintenance of equipment and acquisition of new equipment for DRR & R.

  • The failure of law enforcing agencies and local authorities to enforce building codes and standards/norms to reduce landslide risks, seems to be very apparent in these studies. Illegally raised additional floors and the owners’ practices of using the basements for residential purposes (which are meant to be non-habitable) are some of the observations supporting the above argument. Some hotel owners even dug up basements while others have put the closed basement to inappropriate use. It also includes the constructions on drains to pave the way for multi-storey structures, which cause seepage and make the foundations weak. Illegal domestic water and electric connections in such buildings indicate lackadaisical attitude of the local officials in dealing with such violations.

  • Forest serves not only as property markers but also as ecological barriers. Forest should be kept thick in places where it is “too steep to plant:”

  • Continuous rainfall and decades of weathering of the slope mass deteriorates the slope stability through a gradual process that may take several years to culminate in a landslides

  • Hefty use of pesticides, chemicals and herbicides, may also degrade the soil mass quality and stability

  • Relocate settlements and infrastructure that fall in landslide prone zones. Microlevel mapping of geotechnical parameters should be done for extensive landuse planning. Construction in dormant or passive landslide areas should be discouraged for human settlements

  • Construction of buildings in areas with critical slope stability conditions should be prohibited or permitted with adequate prevention and mitigation measures. Constructions in very high and high landslide hazard zones should be preferably avoided. Shift settlements away from hazardous slopes and rebuild at safe sites in less hazardous zone.

  • Launch a landslide campaign in the villages/habitats located in fragile landslide prone environment. Conduct regular contact programmes for public awareness on landslides and related hazards, particularly during the pre-monsoon season. Implement safe and scientific methods of slope modification and stabilization.

  • Identify stable ground for safe construction and urbanization with proper drainage measures and protection structures.

  • Rock/Debris Deflectors to protect important infrastructures like bridges

  • During rainy season, the traffic movements should be managed under strict onsite and offsite slope monitoring. Sign boards/banners at appropriately identified vulnerable locations for cautioning the commuters.

  • Altering the geometry of unstable slopes by flattening and benching along with drainage to prevent ingress of water into the slopes

  • Widespread advance communication/warning to dwellers/visitors regarding potential landslides should be done during expected landslide periods.

  • Mainstream disaster risk reduction (DRR) into new development programmes and regularly monitor DRR actions to minimize future risks

  • The stability of dams near the crash zones, should be properly monitored. Any evidence of piping erosion from the debris dams also need to be closely monitored. Monitoring of rivers for floods in the area should also be considered in view of secondary landslides.

  • The roots play an important role in the stability of slopes through penetration and holding of soil particles together

  • Though the local authority was prompt in response to landslides yet they are not well aware about mitigation funds and schemes that can be used to mitigate landslide risks.

  • All terraced slopes should have weeping holes along the terrace walls that would partly prevent the occurrence and persistence of high perched water levels

  • Overhanging regolith material should be terraced, covered with coir geotextiles and planted with deep rooting native grass and shrubs like Vetiver grass (Chrysopogon Zizanioides), lemon grass (Cymbopogon Citrates) that may be used to offer significant root reinforcement to ensure stability

  • Establish demonstrative best practices of landslides management. Environment friendly human settlements with least potential landslide hazards, must be encouraged. Rethink policies from an environmental perspectives to preserve nature and protect lives and livelihoods. Afforestation should be taken up to restore the ecological balance.

  • Better regulations and enforcement for landuse, construction and development, including policy, advocacy, implementation, monitoring and management. Stringent laws must be enacted for construction, development, maintenance and management of infrastructure in the landslide affected areas.

  • Training and Capacity Enhancement in the field of landslides risk reduction and resilience at local levels is very much required. There is a dire need for coordination, networking and linkage among different stakeholders (National Landslide Risk Management Strategy 2019) working on landslides management including public works department, irrigation and flood control, department of geology and mines, Geological Survey of India, Disaster Management Authorities at district, state and national levels etc.