DROUGHT

Drought is a period or condition of unusually dry weather within a geographic area where rainfall is normally present. Droughts occur in all climatic zones. However, its characteristics vary significantly from one region to another. Drought usually results in a water shortage that seriously interferes with human activity. Water-supply reservoirs empty, wells dry up, and crop damage ensues. Its seriousness depends on the degree of the water shortage, size of area affected, and the duration and warmth of the dry period.

CAUSES

      1. Water vapor condenses only if air rises into the colder regions of the atmosphere. If the air doesn’t rise, then no rain will form. When there is high air pressure, air falls instead of rising. With the air pressing down in a high pressure zone, no currents of water vapor are carried upward. As a result, no condensation occurs, and little rain falls to earth.

      2. Most precipitation depends on water vapor carried by winds from an ocean or other source of moisture. If these moisture-carrying winds are replaced by winds from a dry region or flow in different directions, the weather is abnormally dry and often persistently cloudless.

      3. Mountains can prevent wind from blowing moisture to needed regions. As air is moving past a mountain range, it is forced to rise in order to pass over the peaks. However, as the air rises, it becomes colder and the vapor condenses into rain or snow. The rain then falls on that side of the mountain, known as the windward side (the side that is turned toward the wind). When the air mass finally makes it over the mountain, it has lost much of its vapor. This is another reason why many deserts are found on the side of a mountain facing away from the ocean. This phenomenon is known as the rain shadow effect.

IMPACTS 


a) Environmental: - Some direct impacts of drought are reduced crop and forest productivity, reduced ground water levels, increased fire hazard, increased livestock and wildlife death rates, and damage to wildlife and fish habitat. Drought is also associated with increases in insect infestations and plant disease. Forest fires increase dramatically during periods of droughts. 
b) Economic: - A reduction in crop productivity usually results in less income for farmers, increased prices for food, unemployment, and migration. 
c) Social: - Social impacts include health, public safety, conflicts between water users, and reduced quality of life. During droughts many people migrate to areas outside the drought-affected location. When this happens, the area loses a great deal of its population, and thus the area has less financial support. Between 1950 and 1980 the drought of Brazil had a loss of 5.5 million people. This continues to be a significant problem in the economic development of Brazil.

WARNING AND DISSEMINATION

There is a "Weather-Watch-Group" in the Ministry of Agriculture, which meets every week to take stock of the rainfall progress, its effects on the crops from sowing to harvesting, during the kharif season. Weekly input gives an early warning about the impending drought as and when symptoms arise in this regard and the states are warned accordingly. The drought assessment is based on a comparative evaluation of satellite observed green vegetation cover (both area and greenness) of a district in any specific time period, with that of any similar period in previous years.

PREVENTION

Although drought cannot be reliably predicted, certain precautions can be taken in drought-risk areas. It is important to develop strategies to protect from drought. Strategies for drought protection, mitigation or relief include:

1. Construction of Dams:

The construction of dams is a better choice to avoid drought. Dams work by storing the extra water when it is available, so that during a time of drought, it can be released. It is done both to prevent drought and to prevent flooding. The main purpose of most dams is to create a permanent reservoir of water for use at a later time. The dam must be watertight (i.e. impermeable or impervious to water) so that water does not leak out of the dam and escape downstream. An essential part of a dam is therefore the "impermeable membrane", i.e. the watertight part of the dam that prevents water leaking out.

2. Cloud seeding:

Cloud seeding is the process of spreading either dry ice, or more commonly, silver iodide aerosols, into the upper part of clouds to try to stimulate the precipitation process and form rain. Since most rainfall starts through the growth of ice crystals from super-cooled cloud droplets (droplets colder than the freezing point, 32 deg. F or 0 deg. C) in the upper parts of clouds, the silver iodide particles are meant to encourage the growth of new ice particles. The history of cloud seeding has experienced uncertain results because it can never be known whether a cloud that rains after seeding might have rained anyway. This is because seeding is performed on clouds that look like they have some potential for producing rain.

3. Desalination:

It is the process of removing soluble salts from water to render it suitable for drinking, irrigation, or industrial uses. The principal methods used for desalination include distillation (or evaporation), electro dialysis, freezing, ion exchange, and reverse osmosis.

4. Rainwater Harvesting:

Broadly rainwater can be harvested for two purposes

·                   Storing rainwater for ready use in containers above and below ground.

·                   Charged into soil for withdrawal later.

Rainwater harvesting can be harvested from the following surfaces 
               Roofftops.

                   Paved and unpaved areas.

·                  Water bodies.

                   Storm water drains.

The decision whether to store or recharge water depends on the rainfall pattern and the potential to do so, in a particular region. The sub-surface geology also plays an important role in making this decision.

5. Recycled water:

The use of recycled water in horticulture (urban and rural) and industry, as well as in residential areas has grown considerably over the past decade. Recycled water is water from the city or sewage that is then treated and reused. No potable water, not suited for drinking, is reused on a daily basis in some cities. It can be used for such things as car washes, laundry facilities, road cleaning, firefighting and toilet flushing. No potable water reuse is most beneficial in cities when irrigation is in full swing at ball fields, golf courses, parks, schoolyards and residential lawns. Using reclaimed water for irrigation has a marked difference on potable water levels during these months.

6. Other small scale methods:

a. Mulching

Mulches like UV stabilized poly-sheets have become the major input for growing crops. Such sheets reflect the sunlight and causes minimum soil moisture evaporation. Israel is the leading country adopting this method with very high productivity.

b. Coconut Compost

India has plenty of resources to tackle soil moisture retention like the coconut compost. When the coconut husk is composted and added to soil, the coconut fibre absorbs moisture from the soil and retails for a long period releasing moisture gradually to crops. This technology has made farming in drought prone areas very simple. Many coconut husk processing units in Tamil Nadu like Pollachi is taking advantage and exports several thousand tons of coconut compost to countries like Israel which uses as a media in green houses for growing roses, vegetables and fruits.

c. Water Aquifers

Water aquifers are made to recharge the ground water without wasting the rain water. Aquifers are simple methods of percolation by which small bore wells are dug and the inner surface is perforated and filled with gravel to absorb the rain water. The rain water percolates deep into the ground and recharges the ground water.

FAMOUS DROUGHTS

      
      1. When pione­ers headed west in the late 19th century, many couldn't resist the lure of the tall gras­sy land in the semiarid midwestern and southern plains of the United States. They settled there to farm. They were prosperous in the decades that followed, but when the 1930s rolled in, so did strong winds, drought and clouds of dust that plagued nearly 75 percent of the United States between 1931 and 1939 [source: PBS]. The era became known as the legendary Dust Bowl. The Dust Bowl brought ecological, economical and human misery to America during a time when it was already suffering under the Great Depression.

      
      2. There was a major drought in the Sahel, Africa in 1914, caused by annual rains far below average that caused a large-scale famine. As another long drought-period from 1968 through 1974 began, the grazing quickly became unsustainable, and large-scale denuding of the terrain followed. Like the drought in 1914, this led to a large-scale famine, but this time it was somewhat tempered by international visibility and an outpouring of aid. This catastrophe led to the founding of the International Fund for Agricultural Development. In June to August, 2010, famine struck the Sahel again. Niger's crops failed to mature in the heat, and famine occurred. 350,000 faced starvation, and 1,200,000 were at risk of famine.