Tuesday, December 10, 2013

Disaster Management & Mitigation - UNIT-II


NATURAL DISASTERS

HYDRO-METEOROLOGICAL DISASTERS
Hydrometeorology is a branch of meteorology and hydrology that studies the transfer of water and energy between the land surface and the lower atmosphere. UNESCO [1] has several programmes and activities in place that deal with the study of natural hazards of hydrometeorological origin and the mitigation of their effects. Among these hazards, the results of natural processes or phenomena of atmospheric, hydrological or oceanographic nature, are floods, tropical cyclones, drought and desertification. Many countries have established an operational hydrometeorological capability to assist with forecasting, warning and informing the public of these developing hazards.

TROPICAL CYCLONES
A tropical cyclone is a rapidly-rotating storm system characterized by a low-pressure center, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain. The term "tropical" refers to the geographical origin of these systems, which usually form over the tropical oceans. The term "cyclone" refers to their cyclonic nature, with wind blowing counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. The opposite direction of circulation is due to the Coriolis force. Depending on its location and strength, a tropical cyclone is referred to by names such as hurricane, typhoon, tropical storm, cyclonic storm, tropical depression, and simply cyclone. In addition to strong winds and rain, tropical cyclones are capable of generating high waves, damaging storm surge, and tornadoes. They typically weaken rapidly over land. Therefore, coastal regions are particularly vulnerable to damage from a tropical cyclone as compared to inland regions. Though their effects on human populations are often devastating, tropical cyclones can relieve drought conditions. They also carry heat energy away from the tropics and transport it toward temperate latitudes, which plays an important role in modulating regional and global climate. 

 FLOODS
A flood is an overflow of water that submerges land which is usually dry. Flooding may occur as an overflow of water from water bodies, such as ariver or lake, in which the water overtops or breaks levees, resulting in some of that water escaping its usual boundaries,[3] or it may occur due to an accumulation of rainwater on saturated ground in an areal flood. Floods can also occur in rivers when the flow rate exceeds the capacity of the river channel, particularly at bends or meanders in the waterway. Floods often cause damage to homes and businesses if they are in the natural flood plains of rivers. Some floods develop slowly, while others such as flash floods, can develop in just a few minutes and without visible signs of rain. 
Areal Flood

  1. Floods can happen on flat or low-lying areas when the ground is saturated and water either cannot run off or cannot run off quickly enough to stop accumulating. 
  2. Floods can also occur if water falls on an impermeable surface, such as concrete, paving or frozen ground, and cannot rapidly dissipate into the ground.
  3. Localized heavy rain from a series of storms moving over the same area can cause areal flash flooding when the rate of rainfall exceeds the drainage capacity of the area. This can sometimes result in a muddy flood.
Riverine Flood
  1. Slow rising floods most commonly occur in large rivers with large catchment areas. The increase in flow may be the result of sustained rainfall, rapid snow melt, monsoons, or tropical cyclones. Localised flooding may be caused or worsened due to drainage obstructions such as landslides, ice, or debris.
  2. Rapid flooding events, including flash floods, occur on smaller rivers, rivers with steep valleys or rivers that flow for a long distance over impermeable terrain. The cause may be localized precipitation or sudden release from an upstream impoundment created behind a dam, landslide, or glacier.
Estuarine and coastal
  1. Flooding in estuaries is commonly caused by a combination of sea tidal surges caused bywinds and low barometric pressure, and they may be worsened by high upstream river flow.
  2. Coastal areas may be flooded by storm events at sea
  3. Urban flooding is the inundation of land or property in a built environment, particularly in more densely populated areas, caused by rainfall overwhelming the capacity of drainage systems, such as storm sewers
  4. Catastrophic flooding is usually associated with major infrastructure failures such as the collapse of a dam, but they may also be caused by damage sustained in an earthquake or volcanic eruption.


DROUGHT & DESERTIFICATION
Drought is an extended period when a region notes a deficiency in its water supply whether surface or underground water. A drought can last for months or years, or may be declared after as few as 15 days. Generally, this occurs when a region receives consistently below average precipitation. It can have a substantial impact on the ecosystem and agriculture of the affected region. This global phenomenon has a widespread impact on agriculture. 
Periods of droughts can have significant environmental, agricultural, health, economic and social consequences. The effect varies according to vulnerability. For example, subsistence farmers are more likely to migrate during drought because they do not have alternative food sources. Areas with populations that depend on as a major food source are more vulnerable to famine.
Drought can also reduce water quality, because lower water flows reduce dilution of pollutants and increase contamination of remaining water sources. Common consequences of drought include:

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