Much of the United States has been in
drought during 2002. This has impacted virtually
all segments of our society, from industrial production and jobs to
recreation and tourism.
According to Robin Clarke and Jannet King, The
Water Atlas, ISBN 1-56584-907-8:
"Droughts do not happen overnight; they may
take several years to develop. A drought in one region might be
three weeks without rain; in another it might be no rain for a
year."
They further state "The lives of one billion
people, a sixth of the world's population are threatened by droughts and
desertification. Climate change is making the situation worse."
Since water is not evenly distributed over the
earth's land masses, many people live in areas where water is in short
supply. As the population increases, the likelihood of water shortages
increases.
Drought can be hydrologic, agricultural or
historic. Hydrologic drought is compared to precipitation and runoff
records from the past. Agricultural drought is one where the local
plants get too little rainfall based on their optimum amount. Historic
drought is based on total water records from the past (runoff,
precipitation etc.). These are not the same and have very different
impacts on humans.
For example, an agricultural drought could occur,
where the people have enough to drink, but the local food crops are
dying for lack of precipitation. A hydrologic drought could happen,
where water supplies were adequate for humans, plants and animals.
However, the runoff and precipitation amounts were much less than the
norm.
People normally think of droughts occurring in a
desert. However, rainforests, and temperate regions of the earth are
also prone to drought. For example, the Florida Everglades is
experiencing a drought. This is a semi-tropical to tropical ecosystem.
Droughts in these areas are often more devastating than those in
semi-arid or arid regions, because the plants and animals are not used
to having less water.
To further put things into perspective, I have
included some fresh water estimates below.
Some fresh water estimates
The following are sources of fresh water:
Glaciers, snow, ice and permafrost -
unavailable - 69.3%
Lakes, rivers, soil moisture, air humidity,
plants and animals - available - 0.4%
Groundwater - available - 30.1%
Note that the largest percentage is not available
for human consumption.
Add to this that 97.5% of the Earth's water is
either salt water or briney water, with fresh water being only 2.5% of
the total. It is estimated that 119,000 km3 per year falls on
the land masses, while 458,000 km3 per year falls on salt
water.
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