Natural Hazards and Disasters: Mitigation Strategies

A hazard is a potentially damaging physical event, phenomenon or human activity, such as an earthquake, a cyclone or a chemical leak. Exposure is the presence of people, property and systems in the path of a hazard, vulnerability is the degree to which they are likely to be harmed, and capacity is the strength and resources available to cope. A disaster occurs when a hazard strikes a vulnerable and exposed community that cannot cope with its own resources. This is summarized as Risk = Hazard x Vulnerability / Capacity, which shows that risk can be reduced even when hazards cannot be prevented, by reducing vulnerability and increasing capacity. That is the logic of mitigation and of disaster risk reduction (DRR): the same cyclone kills far fewer people in a place with warning systems, shelters and strong houses than in a place without them.

Hazards are classified as geophysical (earthquake, volcano, tsunami, landslide), hydro-meteorological (cyclone, flood, drought, heat wave, cold wave, lightning, hailstorm, avalanche), climatological (wildfire), biological (epidemic, pest attacks), and human-made or technological (industrial and chemical accidents, nuclear accidents, oil spills, fires, stampedes). Disaster management is described as a cycle of four phases: mitigation (reducing or limiting adverse effects, before the event), preparedness (plans, training, early warning, stockpiles), response (rescue, relief, first aid) and recovery (rehabilitation and reconstruction, ideally 'build back better').

• Focus (hypocentre) is the point of origin inside the Earth; epicentre is the point on the surface directly above it; instrument is the seismograph

• Seismic waves: P waves (primary, fastest, compressional), S waves (secondary, shear, cannot pass through liquids), surface waves (slowest, cause most damage)

• Richter scale measures magnitude and is logarithmic; Modified Mercalli scale measures intensity (I to XII) from observed effects

• India's seismic zones: Zones II, III, IV and V, with Zone V the most hazardous (Himalaya, north-east, Rann of Kachchh); the Himalaya is earthquake-prone because the Indian plate is colliding with the Eurasian plate

• Notable Indian earthquakes: Uttarkashi 1991, Latur (Killari) 1993, Bhuj 2001 (26 January), Kashmir 2005

• Indian standards: IS 1893 for earthquake-resistant design, with IS 4326 and IS 13920 for construction and ductile detailing

• Tsunami: sea waves generated mostly by submarine earthquakes (also landslides and volcanoes); the 26 December 2004 Indian Ocean tsunami followed an earthquake off Sumatra; the Indian Tsunami Early Warning Centre is at INCOIS, Hyderabad

• Ring of Fire is the volcanic and seismic belt around the Pacific; Barren Island in the Andaman Sea is India's only active volcano

• Tropical cyclones are called hurricanes in the Atlantic, typhoons in the north-west Pacific and cyclones in the Indian Ocean; in India warnings come from the India Meteorological Department

• The main killer in cyclones is the storm surge, a rise in sea level caused by strong winds and low pressure; the Odisha Super Cyclone occurred in October 1999

• Floods: the Kosi is called the Sorrow of Bihar and the Brahmaputra causes yearly floods in Assam; flash floods are rapid-onset floods; Glacial Lake Outburst Floods (GLOF) occur when glacial lake dams fail; Kedarnath (2013, Uttarakhand) combined heavy rain, flash floods and landslides

• Drought types: meteorological (rainfall deficiency), hydrological (low streamflow and groundwater), agricultural (soil moisture and crop failure), socio-economic

• Landslides occur mostly in the Himalaya, north-east and Western Ghats; human triggers include slope cutting for roads, deforestation and blocking of natural drainage

• Heat waves: Ahmedabad's Heat Action Plan (2013) was the first in South Asia; forest fires are controlled by fire lines and firebreaks

The Sendai Framework for Disaster Risk Reduction (adopted March 2015 in Sendai, Japan) has four priorities for action and seven global targets:

1. Understanding disaster risk

2. Strengthening disaster risk governance to manage disaster risk

3. Investing in disaster risk reduction for resilience

4. Enhancing disaster preparedness for effective response and to Build Back Better in recovery, rehabilitation and reconstruction

The seven targets aim to reduce disaster mortality, the number of affected people, direct economic loss and damage to critical infrastructure by 2030, and to increase the number of countries with national and local DRR strategies, international cooperation and availability of multi-hazard early warning systems.