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Drought
by Dave Beste
The importance of water is obvious enough, but what frequently goes
unappreciated is it's frequent accessibility. It is an element that
exists as a solid one minute and within a matter of seconds can
change to a liquid and then a gas. It exists everywhere; as water
vapor in the atmosphere, miles of packed ice at the Poles, a nearby
river, or pouring out of the faucet.
Popular opinion as to how water maintains it's balance in the environment
is unfortunately cluttered with half truths and misunderstandings.
Even less is understood about it's fragile state and how easily
a natural disaster; such as a drought, can occur.
About 97.5% of all water exists in the oceans, while amazingly only
.001% exists at any given time in the atmosphere. The constant transfer
of water among the land, oceans, and atmosphere is called the hydrologic
cycle.
 The
cycle is an example of nature, yet again, working in true harmony.
It is a well orchestrated process that works to maintain balance
in the environment and helps to sustain a world that depends largely
on water for survival.
The hydrologic cycle begins with evaporation, which is the changing
of water from a liquid to a gas. A large majority of evaporated
water comes from the ocean, while about one-fifth comes from plants
and smaller inland water sources.
While the water ascends into the atmosphere as water vapor it begins
to cool in a process called condensation and again takes on a liquid
form, producing cloud droplets.
Although some water is found in clouds, a majority of it still exists
as water vapor that is carried through the atmosphere by strong
winds; such as the jet stream. This step is called transport and
is responsible for moving water throughout the atmosphere and across
the country.
Water returns to the Earth through precipitation, which can occur
in various forms from rain, sleet, snow, etc.. The yearly amount
of precipitation released on a region may vary greatly with the
amount in another nearby region depending on the topography of the
area. A natural wonder; such as, the Rocky Mountains may trap and
prevent the movement of precipitation from one place to another.
This can result in a huge discrepancy in precipitation totals between
locations separated by only a couple hundred miles.
Once it has fallen to the ground, and thus become groundwater, there
are a few different possibilities as to where it could go. Groundwater
could continue moving downward, below the surface, until it hits
a layer of impermeable rock and then travel laterally along this
rock layer until it is deposited into a lake, river, or other large
body of water. The location where this lateral movement takes place
is called an aquifer and is an extremely slow process usually measured
in meters or even centimeters for an entire year.
 As
the groundwater seeps through the surface it must move through two
major sections before reaching the layer of impermeable rock: the
zone of aeration and the zone of saturation. The zone of aeration
is closer to the surface has crevices filled with a mixture of both
water and air; while the crevices in the zone of saturation are
filled only with water. Dividing the two layers is the water table.
As precipitation increases in an area and the ground becomes more
saturated the water table climbs nearer to the surface. Once the
water table meets the surface flooding occurs since there is no
room for the excess groundwater.
Not all precipitation that falls on land becomes groundwater. The
water which does not make it's way into the soil or evaporate becomes
runoff. This water is carried along the land in search of one larger
body of water after another, until it eventually empties out into
the ocean and evaporates; continuing the cycle.
Groundwater may also undergo transpiration, which is a function
used by plants to reintroduce water into the atmosphere. The plants
move the water up through their roots and release it in a gaseous
form through stomata located on their leaves. This process can account
for as much as ten percent of all evaporated water.
The water cycle is constant, but still very fragile. It does not
require much for the cycle to be disrupted and the desired water
supply becomes dramatically reduced. There are multiple reasons
as to why a drought may occur. Poor land use, deforestation, wars,
cash cropping, unprovoked climate changes, and an ever increasing
demand for water from an ever increasing population are a few of
the many variables that can help to enhance the severity of a drought.
 Droughts
are not random occurrences, although they cannot be definitively
forecasted, and result from a combination of specific conditions
the same as any natural disaster. According to the PDSI, Palmer
Drought Severity Index, from 1895-1995 every area of the continental
United States had experienced a "severe and extreme drought"
at one time. Some areas have been devastated more than others, but
it is important to remember that droughts are not prone only in
arid desert-like areas. There are definitive reasons why droughts
occur when they do and although some parts of the country have a
reputation for attracting every rain cloud in the sky, almost every
place on the planet is susceptible to the damaging affects of a
drought.
There are basically four types of droughts, which depending on the
droughts severity eventually will affect the community at large.
It begins as a meteorological drought, which is simply a large deficiency
in precipitation over an allotted amount of time. As this type of
drought progresses it lends itself to an agricultural drought, which
incapacitates crop growth due to insufficient soil moisture. A hydrological
drought is noticed well after an agricultural drought and can be
recognized by a noticeable reduction in the water levels of rivers,
lakes, and other large bodies of water. Beyond a hydrological drought
is a socioeconomic drought; wherein the massive depletion of water
can have catastrophic consequences, affecting society in almost
every aspect.
Of course not all droughts are so destabilizing that they have a
crushing impact on the local community. But many do and their affects
can be far reaching, directly pervading not only the environment,
but also social and economic areas.
Landscapes are ravaged by fire and erosion. While plant and animal
species suffer disease and depletion of numbers. Malnutrition results
from food shortages and illness becomes more prevalent. In many
nations the duress experienced from living in a drought stricken
area has instigated social unrest and conflicts. In addition, large
amounts of profits are lost to people who depend on agriculture
and farming, which can have serious repercussions to the economy.
Scientists have determined that there have been periods in history
when a drought has sustained itself for one hundred years or more.
Such a prolonged drought would have unthinkable consequences today.
The most horrific drought on U.S. soil in recent times was the Dust
Bowl of the 1930's. Lasting over ten years the Dust Bowl was a lethal
combination of intense heat, wind, and a severe lack of precipitation.
Farmers helped to worsen the drought by overworking fields and letting
animals graze over huge areas of land. The area that constitutes
the Dust Bowl is more subject to drought like conditions because
of increased water evaporation, resulting from the same types of
strong winds along the Plains and low levels of precipitation that
helped create the hardships of the 1930's.
Droughts are not preventable natural occurrences, but the harshness
of their impact can be reduced by recognizing the consequences of
not conserving. Water is a precious element vital to our existence,
and it is important to understand how it is constantly moving and
working to continue it's cycle.
For More Information:
National
Drought Mitigation Center
DEP
Drought Information Center- Pennsylvania
The
Hydrologic Cycle
About
the Dust Bowl
Surviving
the Dust Bowl
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See past topics of National Watersheds here!
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