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EDITORIAL 14 ET Estimates in the New West
<br />The term `New West' has been
<br />used in recent years to refer to
<br />developments that are redefining the
<br />social, cultural and environmental
<br />character of the western United States.
<br />Many of the changes bring with them
<br />pressures to allocate water, via will-
<br />ing buyer and willing seller and other
<br />means, to water uses that are different
<br />from those traditionally supported in
<br />the `Old West.' These include a shift
<br />in water resources from traditional
<br />irrigated agriculture to new urban,
<br />recreational and environmental uses.
<br />As with most changes, there are
<br />unintended consequences associated
<br />with new water uses in the New West.
<br />In some places, irrigated agriculture
<br />is being greatly reduced with corre-
<br />sponding landscape, social, and cul-
<br />tural changes to the Old West — chang-
<br />es that are increasingly viewed with
<br />concern, not only in local communities
<br />bearing the brunt of the impact, but
<br />also by the larger population. Is there
<br />a way to meet emerging New West
<br />water needs while not eliminating, or
<br />damaging, the economic viability of
<br />the Old West uses of water?
<br />To begin to answer the question, it
<br />may be helpful to step back from the
<br />immediate water shifts and conse-
<br />quences and examine the total water
<br />use picture in Colorado; and then,
<br />point out the needs for new water
<br />knowledge to move toward a better
<br />water balance between the New and
<br />Old West.
<br />The water resources available for use
<br />in Colorado are derived, almost exclu-
<br />sively, from precipitation that falls on
<br />the Colorado's land mass — Colorado,
<br />truly, is a `headwaters' state. As noted
<br />in the article on page 5 of this issue of
<br />Colorado Water, Colorado receives an
<br />average 95 million acre -feet of water
<br />by Robert Ward and Reagan Waskom
<br />each year in the form of precipitation
<br />falling on the land surface. Yet, most
<br />water experts tend to talk of only the
<br />15.6 million acre -feet of water that
<br />flows in our streams, and the 2 million
<br />acre feet of ground water pumped an-
<br />nually, as the sum total of water used in
<br />Colorado. These numbers suggest that
<br />before humans have an opportunity to
<br />access the 95 million acre -feet of water
<br />falling on Colorado, the environment
<br />utilizes roughly 78 percent of the total
<br />water, on average. How does the en-
<br />vironment access this water? -- largely
<br />through transpiration from plant com-
<br />munities and evaporation from land and
<br />water surfaces (collectively referred to
<br />as evapotranspiration).
<br />Furthermore, irrigated agriculture uti-
<br />lizes 84 percent of the water consumed
<br />by human activity in the state each year
<br />(i.e., 5.5 million acre - feet). As with
<br />nature's use of water, agricultural water
<br />is consumed by evapotranspiration.
<br />The above view of water availability
<br />and use reveals that evapotranspira-
<br />tion, be it by the environment or by
<br />agriculture, consumes a lot of the water
<br />that falls on our state. Unfortunately,
<br />measuring the exact amount of water
<br />consumed by evapotranspiration is not
<br />nearly as easy as measuring the amount
<br />of water diverted from a stream or the
<br />amount pumped from a well.
<br />Estimating evapotranspiration is not a
<br />new research subject in Colorado. In
<br />fact, the State Agricultural College's
<br />Bulletin Number 1, published in 1887
<br />and authored by Professor Elwood
<br />Mead, is titled: "Experiments in Irriga-
<br />tion and Meteorology" - an early study
<br />of evaporation measurements near
<br />irrigated fields. CWRRI alone, over
<br />the past 39 years, has published the
<br />results of a number of studies that ad-
<br />dress evapotranspiration - related topics
<br />(the list of reports is presented on the
<br />CWRRI website located at www.cwrri
<br />.colostate.edu).
<br />While there has been a considerable
<br />amount of effort in the distant past
<br />to develop scientifically sound ET
<br />estimates in Colorado, there has been
<br />a drop off of effort in recent years.
<br />As a result, when ET estimates are
<br />needed today to settle disputes, they
<br />are computed using crop coefficients
<br />determined in Kimberly, Idaho and
<br />Bushland, Texas (sites of long -term
<br />USDA Agricultural Research Service
<br />measurement programs). Data from
<br />existing weather stations are also re-
<br />quired in the estimates. Are these esti-
<br />mates the best we can obtain? Should
<br />we be doing more to refine Colorado's
<br />ET estimates?
<br />This issue of Colorado Water exam-
<br />ines efforts to estimate evapotranspira-
<br />tion (or ET) in Colorado and explores
<br />issues that should be considered in
<br />any effort to refine ET estimates in the
<br />future.
<br />First, to examine why ET estimates are
<br />currently important to Colorado, the
<br />reader is referred to Dennis Montgom-
<br />ery's South Platte Forum keynote ad-
<br />dress, presented on page 19. Dennis,
<br />using his experience in legal proceed-
<br />ings surrounding compact compliance
<br />in the Arkansas River Basin, makes a
<br />strong case for improving the science
<br />behind today's efforts to estimate ET
<br />in Colorado.
<br />Reagan Waskom presents a large
<br />overview of water use in Colorado,
<br />including the water consumed by
<br />Colorado's native landscape. Dan
<br />Smith and Grant Cardon, on page 7,
<br />explain how plants use water and the
<br />effect increased levels of water salinity
<br />have on plants' ability to use water
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