PUB00106

• Year: 2000
• Title: A History of Drought in Colorado: Lessons Learned and What Lies Ahead
• CWCB Section: Water Conservation & Drought Planning
• Author: Colorado State University
• Description: Lessons learned and what lies ahead
• Publications - Doc Type: Tech Report

How Colorado Gets its Water

Colorado gets new water suppliesl from only one source:
precipitation, in the fonn of rain, hail, or snow. Colorado
gets all of its water from precipitation because there are no
major rivers that flow INTO Colorado.2 There are several
m<:tior river basins. originating in the Colorado Rockies, that
flow OUT of the state, providing water to much of the
southwestern United States, and contributing to the
Missouri and Mississippi rivers as well. Thus, Colorado
earns its title as "the Mother of Rivers."

Although the main source of Colorado's water supplies is
precipitation, Coloradans typically do not use water
directly in the form of precipitation. Usually, water comes
to Colorado as precipitation but is then stoTed in one of
five forms of usable water:

snowpack (SN), used directly for recreation, although
it also serves as a storage of water supplies;
streamflow (ST), used for recreation, habitat, irrigation
and municipal water supplies, as well as to meet
interstate compact obligations~
reservoir water (RW), used similarly to streamflow;
soil moisture (SM), used for natural vegetation and
agriculture; and
groundwater (aW), used for irrigation and municipal
water supplies.

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Thus, some of the brief summer rains that fal) in Colorado
will add little or no water to the usable water supply. Water
can also be stored as snowpack for months before melting
to become streamflow, then reservoir water or groundwater.

There are two natural pathways by which water from
precipitation become a usable source of water supply:

Pathway #1
(esp.lowerelev.)

Pathway #2
(esp. higher elev.)

Precipitation

Precipitation

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SM GW
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Snowpack
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ST RW SM GW

ST RW

The first pathway is that precipitation falls on the ground
and becomes soil moisture (SM) and groundwater (GW) to
support vegetation and other uses locally where it occurs.
A portion may also become streamflow (ST) and reservoir
water (RW). This is the dominant pathway for all lower
elevations of the state and for the higher elevations in the
summer season.

The second pathway is that precipitation falls as snow at
The amount of time it takes for precipitation to turn into a higher elevations in the winter season to become snow-
usable form of water can vary greatly. Precipitation can pack (SN), and later becomes available as streamflow (ST),
add to soil moisture or snowpack almost immediately. reservoir water (RW), soil moisture (SM) and groundwater
However, there can be delays of several days or weeks caW) during the following spring and summer. This is the
before precipitation adds to the water levels in streams, primary pathway by which mountain snows provide
reservoirs. or groundwater aquifers. During those time surface water resources for the state, and results in peak
delays, some precipitation can be lost to evaporation. streamflows occurring from April through July.

I Not including ancient aquifers, such as in the Denver basin, which receive little or no recharge and are being "mined,"
2 Well, OK, there's Little Snake River, which starts in Wyoming, enters Colorado briefly to join the Yampa before leaving for Utah. The
Green River also starts in Wyoming, flows to Utah, then comes into Colorado briefly to join the Yampa before leaving the state again.

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