BOARD01080

• Board Meeting Date: 1/27/2004
• Description: WSP Section - Native Species Trust Fund, Recommendations for FY 2004-05
• Board Meetings - Doc Type: Memo

~olorado Watu Resoun:es Resean:h Institute.

What is drought?

Drought is unique among natural hal..ards because it is not
a clear event. like a flood. earthquake. hurricane or tornado.
These events strikc. lea\'c their mark. and arc gone. A
drought. however. sneaks up on us quietly disguised as
lovely. sunny weather. Unlike a hurricane......e cannot
follow ils course on a map. We are never sure when a
drought began until after it is already .....ell undcrn'ay, and
.....e are oftcn unsure .....hen it cnds. Any day when it
doesn.t......in or sno..... (which describes the majority of day'>
here in Colorado) could be the beginmng of the next
drought.

\Vhich still does not answer our question: what is
drought?

Drought is a concept that is both simple and complex.
Drought is a shonage of water. usually associated with a
deficiency of precipitation. Drought occurs .....hen the
demand for water exceeds the supply of water.

Simple. right"~

Yes. except that differenlty~s of demands require
different amounts of water in different fonns at different
times of the year. Droughts arc often defined by their
impacts. e.g. on crops or on reservoir water levels and
power availability. Thus. there i!'. no universal definition of
a drought. The more diverse the economy and the climate
of a region are, the harder it is to define drought. Drought
means different things to different people; one person's
drought can be another person's "!'.unny day."

Several definilions of droughl have
been proposed by various agencies.
The figure. which is from a publication
by the National Drought Mitigation
Center (http://enso.un I.edulndmcl),
iIIustrales a set of definilions that show
both causes and impacls of droughl
over lime. namely: meleorological
drought. agricultural drought. hydrologi-
cal drought. and socioeconomic <and
em-ironmcntall drought. Another
important definilion of drought con-
cerns wildfire risk. This paper deals
primarily' wilh TTlCleorological drought
and lhe hislory of wet and dry periods
in ColorJdo. However, the impacts of
droughts of different durations. levels
of se\'erity. and areal extent. are also
discussed.

i Preclpltatlon dsflclency
{ (amount. Intllnsrty,uIJung)
,
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I

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Drought is also "relative" and must be defined in tcrms of
what is "nonnal" for a panicular region or time of year. To
someone .....ho has lived in Nevada or Arizona. Colorado
looks mighty green and lush. Folks who just moved here
from the easlern half of the United States. however, may
think that Colorado e.'(periences perpelUal drought. In fact.
for mas! locations east of Omaha or Kansas CiIY. the driest
year on record may still Ix wetter than the wettest year on
record for most of Colorado's lower elevations. Coloradans
have adapted to thie; dry regime.

One important measure of drought is (he impacts of waleI'
shonage on nature and society. These impacts may
change o....er time as new mitigation measures are de....el-
oped. Forexample, many water users in Colorado are able
to store Water o....er time. or transpon water from other parts
of the state, or uc;e groundwater recharge to re-regula!e
streamflows, or make artificial "snow" for ski areas. Since
Colorado receive!'. new .....ater supplies only one way - as
rain. snow. or other precipitation - some fonn ofprecipita-
tion is necessary to provide water to Colorado's population
and economy. That precipitation. however, does not
necessarily fall on the population!'. that use the waler mos(
or at the times when it is mml needed.

Understanding - and thus preparing for - a severe drought
in Colorado requires an appreciation of how Colorado
receives its water supply and how different water demands
U'>C that supply. This paper presents a discussion of
Colorado's water supplies and demands, and an analysis of
the hislory of wet and dry periods in Colorado.

N3tlJfat Clmate va. lability

Hgh llilmp" high wind.. 10....
relotJve humidly, ",r:der
....n..In..I... cloud co.....

jj
~-
.fi.
~~
,0

Reduc8d InntU'allon, runoH,
deep percOlaUoo. and
gfOllfld water recharge

Inaus8d hapCll"ation
and Ir'atlon

--------------

SaJl'Wst8r deficiency

..1
h
a2S
. I
-------I~J
h'
e ~.
1'.0
':

Plant water strssa, reckiC8d
biOmsSA atld Isld

Reduced streamftaw, Inflow to
re!I8fVOirS, lat", and palM:
reduced Wtltll!lnds,
....ildll!'aMbllBt

--------- ---- --------- ------.

ECOf'Iomic Impacts.

Soelallmpacts EnvirOrlmantallmpacts.

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