Visualizing a Safer Planet
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What is drought?
Sometimes, a natural hazard is a shortage of something, such as water in the case of drought. A drought is an extended period of depleted soil water. Usually, a drought occurs when more water is taken out of the soil than is added to it. This is often the result of a combination of many days without rain and excessive use of water for human activities. One of the greatest threats to people from a drought occurs when agricultural regions receive unusually low amounts of rain, causing vegetation to become dry. When this happens, crop yields can decrease dramatically, often resulting in increased food prices, food shortages, and even famine. At the same time, decreased drinking water quality and availability puts additional strains on our health. In developing countries, the ensuing malnutrition and famine can lead to outbreaks of disease and political conflict. As population and affluence increase, the demand for food and water increases, thereby increasing the probability of drought. Additionally, when vegetation becomes dry during a drought, wildland fire risk increases, threatening homes, crops, and the lives of people and wildlife. Wind can reduce visibility during a drought by blowing loose, dry soil into the air, causing transportation delays and accidents. Droughts can last from days to years. Their duration is controlled by the amount of precipitation received, how much evaporation occurs after precipitation, and how much water is diverted for human consumption.
Where does drought occur?
In North America, several major droughts have occurred in the northern
Rocky Mountain region including Montana, Idaho, Wyoming, southern
Alberta, eastern Washington, eastern Oregon, and the northern portions
of Utah, Colorado, and Nevada. Northern and central Mexico has also
experienced many droughts. Perhaps the greatest area of concern is the
Great Plains of the United States, which plays a vital role in
agricultural production. Parts of Nebraska, Oklahoma, Kansas, Iowa,
Missouri, and Illinois have all experienced several major droughts,
each of which had noticeable impacts on food costs and food supplies
throughout the United States. Most agricultural crops are grown in the
semi-arid and humid regions of the world. Droughts in either of these
regions can pose an immediate threat to agricultural productivity and
threaten human health. With global
warming, droughts are expected to become a major problem for
several agricultural regions. Droughts caused at least $1 billion in
crop damage per year in the U.S. for nine of the 25 years between 1980
and 2005. In semi-arid and arid regions, droughts frequently result in
decreases in drinking water quality and drinking water availability.
When does drought occur?
In areas where most of the winter
precipitation falls in the form of snow, the winter season is
effectively a drought. Water at the surface, and just below the
surface, is frozen for a long period of time and is therefore
unavailable to plants. Many plant species drop their leaves and reduce
growth rates in response to winter drought. From spring through early
fall, plants require water for growth. During this time in arid,
semi-arid, and temperate regions, irrigation is often required to
supplement inadequate rainfall. Also during this time, increased
temperatures cause human water consumption to rise markedly for such
uses as drinking water and cooling. If precipitation remains below
normal for an extended period of time and there is not enough water in
stored in the ground for plant growth, a drought ensues. In general,
droughts present the greatest threat from March through September for
most of North America.
Anywhere in the world, droughts
occurring during the growing season are the greatest threat to people.
In sub-tropical and tropical climates, the growing season is often
determined by precipitation, since temperature is usually high enough
for plant growth all year. Monsoon failures, sometimes related to El
Nino events, can cause extensive crop failures, resulting in drastic
food shortages in regions such as South Asia.
How do we cope with drought?
Coping with water shortages requires a
basic understanding of how the Earth's water cycle operates. There are
usually many inputs and outputs for any reservoir. When too much water
is removed from a reservoir relative to how much is added, a drought
may soon follow. Water conservation is the most effective method for
mitigating droughts. In the United States, water conservation involves
reducing the amount of water used for non-essential activities such as
watering lawns and washing cars. Xeriscaping, which involves planting
drought-tolerant species, is becoming increasingly popular in the dry
western United States. In some regions of the world, water conservation
is a way of life due to typically low rainfall and the absence of a
need for certain non-essential activities (green lawns, etc.). In the
long-term, successful drought mitigation requires assessing the amount
of water available in a region and then adopting a plan of development
that provides for ample reservoir water during dry periods.