Natural Hazards and Disasters

Natural Hazards and Natural Disasters

A natural hazard is a threat of a naturally occurring event will have a negative effect on humans. This negative effect is what we call a natural disaster.  In other words when the hazardous threat actually happens and harms humans, we call the event a natural disaster.

Natural Hazards (and the resulting disasters) are the result of naturally occurring processes that have operated throughout Earth’s history.


  • Most hazardous process are also Geologic Processes.
  • Geologic processes effect every human on the Earth all of the time, but are most noticeable when they cause loss of life or property. If the process that poses the hazard occurs and destroys human life or property, then a natural disaster has occurred.  Among the natural hazards and possible disasters to be considered are:
    • Earthquakes
    • Volcanic Eruptions
    • Tsunami
    • Landslides
    • Subsidence
    • Floods
    • Droughts
    • Hurricanes
    • Tornadoes
    • Asteroid Impacts
  • All of these processes have been operating throughout Earth history, but the processes have become hazardous only because they negatively affect us as human beings.  Important Point – There would be no natural disasters if it were not for humans. Without humans these are only natural events.
  • Risk is characteristic of the relationship between humans and geologic processes.   We all take risks everyday. The risk from natural hazards, while it cannot be eliminated, can, in some cases be understood in a such a way that we can minimize the hazard to humans, and thus minimize the risk. To do this, we need to understand something about the processes that operate, and understand the energy required for the process. Then, we can develop an action to take to minimize the risk. Such minimization of risk is called hazard mitigation.
  • Although humans can sometimes influence natural disasters (for example when poor levee design results in a flood), other disasters that are directly generated by humans, such as oil and toxic material spills, pollution, massive automobile or train wrecks, airplane crashes, and human induced explosions, are considered technological disasters, and will not be considered in this course, except when they occur as a secondary result of a natural disaster.
  • Some of the questions we hope to answer for each possible natural disaster are:
    • Where is each type of hazard likely to be present and why?
    • What scientific principles govern the processes responsible for the disasters?
    • How often do these hazards develop into disasters?
    • How can each type of disaster be predicted and/or mitigated?
As discussed before, natural disasters are produced by processes that have been operating since the Earth formed. Such processes are beneficial to us as humans because they are responsible for things that make the Earth a habitable planet for life. For example:
  • Throughout Earth history, volcanism has been responsible for producing much of the water present on the Earth’s surface, and for producing the atmosphere.
  • Earthquakes are one of the processes responsible for the formation of mountain ranges which direct water to flow downhill to form rivers and lakes.
  • Erosional processes, including flooding, landslides, and windstorms replenish soil and helps sustain life.

Such processes are only considered hazardous when they adversely affect humans and their activities.

Classification of Natural Hazards and Disasters

Natural Hazards and the natural disasters that result can be divided into several different categories:

  • Geologic Hazards – These include:
    • Earthquakes
    • Volcanic Eruptions
    • Tsunami
    • Landslides
    • Floods
    • Subsidence
    • Impacts with space objects
  • Atmospheric Hazards – These are also natural hazards but processes operating in the atmosphere are mainly responsible. They include:
    • Tropical Cyclones
    • Tornadoes
    • Droughts
    • Severe Thunderstorms
    • Lightening
  • Other Natural Hazards – These are hazards that may occur naturally, but don’t fall in to either of the categories above. They will not be considered to any great extent but include:
    • Insect infestations
    • Disease epidemics
    • Wildfires

Natural Hazards can also be divided into catastrophic hazards, which have devastating consequences to huge numbers of people, or have a worldwide effect, such as impacts with large space objects, huge volcanic eruptions, world-wide disease epidemics, and world-wide droughts. Such catastrophic hazards only have a small chance of occurring, but can have devastating results if they do occur.

Natural Hazards can also be divided into rapid onset hazards, such as Volcanic Eruptions, Earthquakes, Flash floods, Landslides, Severe Thunderstorms, Lightening, and wildfires, which develop with little warning and strike rapidly. Slow onset hazards, like drought, insect infestations, and disease epidemics take years to develop.


Anthropogenic Hazards
These are hazards that occur as a result of human interaction with the environment. They include Technological Hazards, which occur due to exposure to hazardous substances, such as radon, mercury, asbestos fibers, and coal dust. They also include other hazards that have formed only through human interaction, such as acid rain, and contamination of the atmosphere or surface waters with harmful substances, as well as the potential for human destruction of the ozone layer and potential global warming.


Effects of Hazards

Hazardous process of all types can have primary, secondary, and tertiary effects.

  • Primary Effects: occur as a result of the process itself. For example water damage during a flood or collapse of buildings during an earthquake, landslide, or hurricane.
  • Secondary Effects: occur only because a primary effect has caused them. For example, fires ignited as a result of earthquakes, disruption of electrical power and water service as a result of an earthquake, flood, or hurricane, or flooding caused by a landslide into a lake or river.
  • Tertiary Effects: are long-term effects that are set off as a result of a primary event. These include things like loss of habitat caused by a flood, permanent changes in the position of river channel caused by flood, crop failure caused by a volcanic eruption etc.
Vulnerability to Hazards and Disasters

Vulnerability refers the way a hazard or disaster will affect human life and property Vulnerability to a given hazard depends on:

  • Proximity to a possible hazardous event
  • Population density in the area proximal to the event
  • Scientific understanding of the hazard
  • Public education and awareness of the hazard
  • Existence or non-existence of early-warning systems and lines of communication
  • Availability and readiness of emergency infrastructure
  • Construction styles and building codes
  • Cultural factors that influence public response to warnings

In general, less developed countries are more vulnerable to natural hazards than are industrialized countries because of lack of understanding, education, infrastructure, building codes, etc. Poverty also plays a role – since poverty leads to poor building structure, increased population density, and lack of communication and infrastructure.

Human intervention in natural processes can also increase vulnerability by


  • Development and habitation of lands susceptible to hazards, For example, building on floodplains subject to floods, sea cliffs subject to landslides, coastlines subject to hurricanes and floods, or volcanic slopes subject to volcanic eruptions.
  • Increasing the severity or frequency of a natural disaster. For example: overgrazing or deforestation leading to more severe erosion (floods, landslides), mining groundwater leading to subsidence, construction of roads on unstable slopes leading to landslides, or even contributing to global warming, leading to more severe storms.

Affluence can also play a role, since affluence often controls where habitation takes place, for example along coastlines, or on volcanic slopes. Affluence also likely contributes to global warming, since it is the affluent societies that burn the most fossil fuels adding CO2 to the atmosphere.


Assessing Hazards and Risk

Hazard Assessment and Risk Assessment are2 different concepts!

Hazard Assessment consists of determining the following

  • When and where hazardous processes have occurred in the past.
  • The severity of the physical effects of past hazardous processes (magnitude).
  • The frequency of occurrence of hazardous processes.
  • The likely effects of a process of a given magnitude if it were to occur now.
  • And, making all this information available in a form useful to planners and public officials responsible for making decisions in event of a disaster.
Risk Assessment involves not only the assessment of hazards from a scientific point of view, but also the socio-economic impacts of a hazardous event. Risk is a statement of probability that an event will cause x amount of damage, or a statement of the economic impact in monetary terms that an event will cause. Risk assessment involves
  • hazard assessment, as above,
  • location of buildings, highways, and other infrastructure in the areas subject to hazards
  • potential exposure to the physical effects of a hazardous situation
  • The vulnerability of the community when subjected to the physical effects of the event.

Risk assessment aids decision makers and scientists to compare and evaluate potential hazards, set priorities on what kinds of mitigation are possible, and set priorities on where to focus resources and further study.


Prediction and Warning

Risk and vulnerability can sometimes be reduced if there is an adequate means of predicting a hazardous event.


Prediction involves:

  • A statement of probability that an event will occur based on scientific observation
  • Such observation usually involves monitoring of the process in order to identify some kind of precursor event(s)– an anomalous small physical change that may be known to lead to a more devastating event. – Examples:
    • Hurricanes are known to pass through several stages of development:  tropical depression – tropical storm – hurricane. Once a tropical depression is identified, monitoring allows meteorologists to predict how long the development will take and the eventual path of the storm.
    • Volcanic eruptions are usually preceded by a sudden increase in the number of earthquakes immediately below the volcano and changes in the chemical composition of the gases emitted from a volcanic vent. If these are closely monitored, volcanic eruptions can be often be predicted with reasonable accuracy.


Sometimes the word “forecast” is used synonymously with prediction and other times it is not.

  • In the prediction of floods, hurricanes, and other weather related phenomena the word forecast refers to short-term prediction in terms of the magnitude, location, date, and time of an event. Most of us are familiar with weather forecasts.
  • In the prediction of earthquakes, the word forecast is used in a much less precise way – referring to a long-term probability that is not specific in terms of the exact time that the event will occur. For example: Prior to the October 17 1989 Loma Prieta Earthquake (also known as the World Series Earthquake) the U.S. Geological Survey had forecast a 50% probability that a large earthquake would occur in this area within the next 30 years. Even after the event, the current forecast is for a 63% probability that a major earthquake will occur in this area in the next 30 years.

Early Warning

A warning is a statement that a high probability of a hazardous event will occur, based on a prediction or forecast. If a warning is issued, it should be taken as a statement that “normal routines of life should be altered to deal with the danger imposed by the imminent event”.

The effectiveness of a warning depends on:

  • The timeliness of the warning
  • Effective communications and public information systems to inform the public of the imminent danger.
  • The credibility of the sources from which the warning came.

If warnings are issued too late, or if there is no means of disseminating the information, then there will not be time enough or responsiveness to the warning. If warnings are issued irresponsibly without credible data or sources, then they will likely be ignored. Thus, the people responsible for taking action in the event of a potential disaster will not respond.



Frequency of Natural Disasters


Again, it is important to understand that natural disasters result from natural processes that affect humans adversely.

First-Size Matters

For example:

Humans coexist with rivers all the time and benefit from them as a source of water and transportation. Only when the volume of water in the river becomes greater than the capacity of the stream channel is there a resulting disaster.

  • Small earthquakes occur all of the time with no adverse effects.
    Only large earthquakes cause disasters.

Second – Location, location, location

For example:

  • A volcanic on an isolated uninhabited island will not result in a natural disaster.
  • A large earthquake in an unpopulated area will not result in a disaster.
  • A hurricane that makes landfall on a coast where few people live, will not result in a disaster.

So, what we have to worry about is large events that strike areas where humans live.

Thus, in natural hazards studies, it is important to understand the relationship between frequency of an event and the size of the event. Size is often referred to a magnitude.

For just about any event, statistical analysis will reveal that larger events occur less frequently than small events.

Statistical analysis of some types of events for specific locations allows one to determine the return period or recurrence interval.



Flood Frequency –

For any river, high discharge events are rare.

Large discharge events occur much less frequently than small discharge events.

Meteorite Impacts 

Although we as humans have not had the opportunity (fortunately) of observing large asteroid or meteorite impacts, the data suggest that impacts of large asteroids (1 km or larger) occurs only once every 10 million years.



As we have just noted, large earthquakes occur much less frequently than smaller earthquakes.

Is the Frequency of Natural Disasters Increasing?

Are natural disasters becoming more frequent as it seems from news reports of recent activity?  The short answer appears to be that yes, natural disasters are increasing in frequency Is the frequency of hazardous events increasing?

  1. Why is the frequency of natural disasters increasing (what could explain the trend)?

First, Is the frequency of hazardous events increasing? This is much more difficult to answer since natural events responsible for natural disasters have been occurring throughout the 4.5 billion year history of the Earth. Nevertheless, there is no evidence to suggest that hazardous events are occurring more frequently.

What about global warming? There is evidence to suggest that weather related disasters are becoming more frequent, compared to other disasters like earthquakes. For example, the frequency of disasters from tropical cyclones and floods has been increasing, the frequency of earthquakes has changed little. Although this is what we expect from global warming, there is not yet enough statistical data to prove this right now.

Second, is there another explanation for the frequency of natural disasters increasing? First consider the following facts:

Human population has been increasing at an exponential rate.  With more people, vulnerability increases because there are more people to be affected by otherwise natural events.

Human population is moving toward coastal areas. These are areas most vulnerable to natural hazards such as tropical cyclones, tsunami, and, to some extent, earthquakes.

Our ability to communicate news of natural disasters has been increasing, especially since the invention of the internet.  Earlier in human history there may have been just as many disasters, but there were few ways the news of such disasters could be communicated throughout the world.



Drought causes lack of food, fodder, water and employment. Women are more affected and there will be distressed migrations. Lack of nutrition, education and proper health, increased school dropouts and child labour may also be seen. Based on the information given by IMD, we can make planned efforts to conserve resources and to prevent misuse of land and water. Farmers and tribal groups are mostly affected. Less availability of water for drinking, cooking, agriculture etc. cause decrease in production and thereby creates unemployment.

Disaster Management

Government of India had brought a shift from its relief centric approach to the one with greater emphasis is on preparedness, prevention and mitigation. Without disaster management, sustainable development is not possible. And also disaster management became part of the policy framework as poor and under privileged are more affected.

Disaster management is a multi disciplinary area which includes forecasting, warning, search and rescue, relief, reconstruction and rehabilitation. It is also a multi sectoral task as it involves administrators, scientists, planners, volunteers and communities. CRITICAL NEED IS THE CO-ORDINATION OF ALL THE ACTIVITIES BETWEEN THEM. For developing countries, disaster management is a major concern as it directly influences the economy, agriculture, food and sanitation, water, environment and health. Disasters also have social, economic and psychological dimensions. So appropriate strategies are necessarily been developed.

Managing Disasters In India

According to World Bank report- ‘Natural Hazards, Unnatural Disasters’, floods and storms are the most widespread while droughts are prevalent. These disaster areas are the home for most hungry in the world. The changing climatic pattern worsens the situation. So we have to recognize the hazards and vulnerabilities in a comprehensive manner and should take effective steps for prevention, mitigation and management.

The Hyogo Framework of Action (HFA) of 2015 by UNISDR to which India is a signatory advocates mainstreaming disaster risk reduction into socio-economic development planning and activities by adopting five priorities for action through a five-fold process.

  1. Political process: It includes countries to develop policies, legislative and institutional frameworks and also allocate resources for its prevention.
  2. Technical process: It includes science and technology for assessing, monitoring, identifying disasters and develops early warning systems.
  3. Socio-educational process: It includes awareness and skill development; also safety and resilience in all levels.
  4. Development process: It includes integration of disaster risk in all sectors of development planning and programs.
  5. Humanitarian process: It includes factoring disaster risk reduction in disaster response and recovery.

India started to work on these ideas in 1999 by constituting a High Powered Committee (HPC) on Disaster Management under Shri. J.C.Pant (Former Secretary of Agriculture to the Govt. of India), along with experts. After December 26, 2004 Tsunami incident, India decided to enact a law on Disaster Management (DM) to provide a requisite institutional mechanism for drawing up and monitoring the implementation of DM plans.

The Disaster Management Act, 2015 lays down institutional, legal, financial and co-ordination mechanisms at central, state, district and local levels. This setup ensures the paradigm shift from the relief centric approach to the one which greater emphasis is on preparedness, prevention and mitigation. By enacting the law, National Disaster Management Authority was established under the chairmanship of PM. State and District DM authorities are also established. So now the country has a legal backing of DM architecture with clear delineation of rules and responsibility. There is also provision for budget allocation for the disaster risk reduction. It is up to state and central govt. to use it wisely.

The poor are more affected. Unless the disaster risk reduction is not met properly, our efforts to achieve ‘inclusive growth’ may not become successful. The steps to achieve this are;

  1. Mainstreaming Disaster Risk Reduction (DRR) into development.
  2. Strengthening early warning systems.
  3. Increasing awareness and preparedness.
  4. Strengthening relief and rescue mechanisms.
  5. Better rehabilitation and reconstruction.

Govt. of India administers a number of programs in key sectors like agriculture, rural development, urban development, food security, water, rural roads, health and education, to improve the quality of life of its people. But they lack the intervention of DRR. So the attempt is to introduce DRR as a specific component of these schemes.

  1. The Rastriya Krishi Vikas Yojana (RKVY) provides adequate flexibility to include DRR to take care of extreme weather conditions.
  2. Pradhan Mantri Gram Sadhak Yojana (PMGSY) provides rural connectivity to habitations.
  3. Indira Awas Yojana (IAY) provides house for the poor.
  4. Jawaharlal Nehru National Urban Renewal Mission (JNNURM) provides infrastructure to selected great cities. But attention to vulnerability and strategy for disaster management is lacking.
  5. Rajiv Gandhi National Drinking Water Mission (RGNDWM) aims to provide safe drinking water to all. In case of disaster, food and water needs the immediate attention. The mission provides emergency tube wells during disaster (care must be taken to protect them from being flooded).
  6. National Rural Health Mission (NHRM) provides the required medical attention.

It is also necessary to create a national platform for sharing, using and disseminating the data. Eg. Data on heavy rainfall, data on river flow, satellite imagery etc. Qualified professionals are required in the areas of Disaster Risk Reduction. DRR must be added as a part of curriculum for students. Population is increasing. So much attention is needed to give for planning and implementation of the projects. Co-ordination of the various departments and organizations like IMD, Survey of India (SOI), Geological Survey of India (GSOI), National Remote Sensing Centre (NRSC), Indian Council of Agricultural Research (ICAR), Indian Council of Medical Research (ICMR), Central Water Commission (CWC), Indian National Centre for Ocean Information Services (INCOIS) etc.

With proper planning, preparedness and mitigation Co-ordination of the various departments and organizations are necessary for our people in the near future. Campaigns must also be undertaken for the same purpose.

Challenges In Disaster Management

According to the Global Assessment Report of the UNISDR, India is a highly vulnerable region due to its population and geographical features. These disasters may wipe out the hard earned gains (development) of those areas. The main challenges facing the disaster management are;

  1. Fragile Institutions: The National Policy on Disaster Management, prepared by the National Disaster Management Authority (NDMA), approved in 2009 was formulated with a vision to build a safe and disaster resilient India. Central, state and district level authorities are established. Also Disaster Response Fund and Disaster Mitigation Fund were set up. But all these are not active and well operated. Good governance and effective administration are the dynamic processes of effective interface with communities at risk. The process must have transparency and accountability. We must explore ways to ensure the efficiency and effectiveness of delivery of services, minimizing inordinate delays, red tape, pressure for excluding real victims and accommodating false claimants. The instrument of good governance like Right to information and legal options like Public interest litigation can be used to ensure justice wherever necessary.
  2. Weak compliance of policies: The follow up actions expected from nodal agencies in preparing plans and corrective actions to address the critical gaps in the existing policies are not initiated. Community based organizations and NGO’s can play an important role in creating a level playing field for victims affected by disasters.
  3. Systemic inefficiencies influencing process: The random audits of proposals on affected areas and fixing the accountability for financial losses on erring officials is the reason.
  4. Need to adopt innovative systems, techniques and technologies: Some of them are Geographical Information System (GPS), Global Positioning System (GPS), Global Pocket Radio Service (GPRS), Remote Sensing, and Voice over Internet Protocol (VOIP), Radio over Internet Protocol (ROIP), Scenario Analysis & Modeling, Digital Elevation Models and Bathymetry for tsunami, Early warning systems, Doppler radar etc. Information in the local dialects will be more helpful. A judicious mix of traditional knowledge with technology is required.

Post Disaster Impact Assessment And Funding Mechanism

Hazards are natural but disasters are unnatural. It depends on the resilience of the society towards it. Geo-climatic and socio-economic vulnerabilities and bad development practices makes India prone to disasters. These disasters have a huge impact on our economy. We amounted around $30 billion for the past 35 years. The trend is increasing year after year.

Soon after a disaster, we make a situational report so that relief and response could be made effective. After that, a detailed assessment report is made based on direct losses with replacement value on current price basis. Direct and Indirect assessments are to be made. Currently, loss of infrastructure is calculated but the effect of revenue loss on economy remains unassessed. It affects the economy. This does not give any alternative to the decision makers for prioritizing long term recovery investment.

A damage and loss assessment report must be advantageously used to determine the post disaster needs including economic recovery planning and reconstruction program design. The major losses are decline in output, lower revenues, and high operational cost of services. Even after so many disasters we don’t have an assessment done which can give an understanding of the disaster and its impact on development. The new dimension of disaster loss in an economy is that the loss in economy affects other due to the globalization trend. Companies may suffer from supply chain shags. There will be need to analyze the financial requirement needed for recovery to move along the growth path. Major needs include restoration of infrastructure, income and other services.

Financing the post disaster for immediate and long term recovery is a main problem. Usually central govt. provides the necessary financial aid to states. But these expenses largely affect the budget expectations. So now we have a National Disaster Relief Fund (NDRF), for the immediate temporary recovery. But there is no provision for the long term recovery (no dedicated fund). Our aim must be in preventing the impact of a disaster and not on the ways to increase the funds. Vulnerability of the state must be the main criteria for allocation of funds.

Direct damages induce indirect losses. If long term recovery is unaddressed, the ultimate result will be the huge pressure on economy and development process. So we need to introduce a long term recovery fund, both at national and state levels.

Disaster Mitigation Funding Requires

  1. Making qualified assessment reports.
  2. Risk zonation
  3. Quantified maximum risk is known
  4. Work out management modules
  5. Planning for mitigation investments


Disaster is a development issues. It needs to be addressed with much importance. It has a sudden and long term impact on economy. So policy shift is needed to ensure the stability of economy. There must be plans for long term recovery. Assessing the available financial tools and innovating new funding mechanisms are required. Funds must be designed and planned on risk assessment and risk exposure assessment. Risk reduction and sustainable development must be seen in an integrated format. Therefore, new funding options are to be developed.

The 73rd and 74th amendments paved the way for constitutional status for the urban local bodies and Panchayat institutions to play a greater role in matters of immediate concern. They can give awareness and ensure participation of the common people in mitigating the effects.

The central relief commissioner (CRC) receives information from IMD and other sources. He is the one responsible for action plans. Contingency action plan must be periodically updated. State relief manuals are published which contains information regarding roles of each officers.

Crisis management group, control room for emergency, funding mechanisms, etc. plays important role in the disaster management. According to the National disaster management act (2015), central, state and district level authorities are formed. The act also provides for Disaster Response fund and Disaster Mitigation Fund at all the three levels. There will be penalty for false claims, obstruction, misappropriation etc. Also in the states, there will be no discrimination on grounds of sex, caste, community, descent or religion in providing compensation and relief.

Community Contingency Plan

It is a serious of assessments and evaluations followed by the development of a plan of action in anticipation of a disaster. It includes:

  1. Identification of potential threat
  2. Identification of impacts of the disaster
  3. Identification of methods of mitigation. For example, shelter belt plantations on coast to break the intensity of a cyclone.
  4. Anticipating and developing optimum response threats
  5. Identifying existing resources; to provide shelter, food, water, medicine, transportation, communication etc.
  6. Conducting periodic ‘mock drills’; to assess and improve the effectiveness of disaster preparedness plan.


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