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A drought is
defined as a prolonged period where little or no rainfall occurs over an
area. Although this definition appears straight forward, understanding
when a drought is developing and how severe the drought will become
involves different factors. These factors include how well the
environment is handling the lack of rainfall, and the time of year that
the event is occurring.
Seasonal
differences are perhaps the most definitive aspects in the development
and intensification of a drought. During the winter, the region may go
several months without any measurable rainfall. However, that does not
mean the area is experiencing a drought. During the winter, the amount
of moisture exchanged between the atmosphere and the soil and plants is
considerably less. The evaporation rate, which is the measure of
moisture dispersed into the atmosphere, decreases during the winter.
Limited sunshine due to the shorter winter days and cooler temperatures
are contributing factors to the lower evaporation rates. Other variables
include wind speed and relative humidity. Typical evaporation rates are
around 0.05 inches per day in the winter, while in the summer, the rate
of water loss per day averages 0.35 inches
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For example, the average rainfall during the month of
June in Lake Charles is around six inches. With a typical
summertime evaporation rate of 0.35 inches per day, the total loss
of water due to evaporation for the month of June would be 10.5
inches. Therefore, given a normal amount of rain for the month, a
deficit of four and a half inches of water will occur. Ideally,
during the winter, the necessary moisture to balance the summer
deficit would be accumulated. Beginning the summer at or above the
normal rainfall is most beneficial.
Finally,
during a drought in the summer, temperatures are typically several
degrees above normal. Increased moisture, via rain, clouds, or wet
ground, allows the temperature to moderate. Without these factors,
temperatures will be warmer. |
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www.nws.noaa.gov 
