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Colorado Water
June 2021
C L I M AT E
C H A N G E &
A D A P TAT I O N
Colorado Water » June 2021 I
Table of CONTENTS
Features—Climate Change and Adaptation From Our Cooperators
3 How is Climate Change Impacting Colorado River Flow 32 The Water Problem: Historical Observations on
By Brad Udall and Dr. Jonathan Overpeck Climate Change
8 Evaluating Conserved Consumptive Use on High- By Taylor Schulze
Elevation Pastures in the Upper Colorado Basin 35 How Has Precipitation Changed Over Time Across
By Dr. Perry Cabot, Aaron Derwingson, and Matt Bromley Colorado?
11 The Agriculture Impact Task Force By Dr. Becky Bolinger
By Nora Flynn 40 Climate Change and Forest Regeneration:
12 Embracing Climate Change in the Colorado Water What to Expect and Where to Go
Plan and in Local Communities By Dr. Ethan Bucholz and Dr. Amanda West Fordham
By Russell Sands Also in this Issue
15 Colorado River Basin Climate and Hydrology: State
of Science, A Synthesis Report to Support Water 46 In Memory of John Porter
Planning and Management By Dr. Melissa Mokry
By Elizabeth Payton and Jeff Lukas 47 Faculty Profile: Dr. Jeremy Rugenstein
19 New Research Explores Hard Truths for the Future of 48 Congratulations to the 2021-2022 CSU Competitive
Colorado River Management Grant Program Awardees
By Eric Kuhn and Lael Gilbert 50 Water Research Awards
23 Climate Change Mainstreaming at Denver Water 52 Water Calendar
By Taylor Winchell and Laurna Kaatz
53 Recent USGS Publications
26 The Colorado Water Plan: Past, Present, and Future
By Rebecca Mitchell Colorado Water
June 2021
References can be found in the online version
C L I M AT E
of this newsletter at watercenter.colostate.edu/
29 Dirty Snow: Turning Qualitative Assessments into
CHANGE &
A D A P TAT I O N
water-news
Quantitative Factors for the Effect of Dust on Snow
On the cover— A campfire on the shore of
By Caroline (Rosie) Duncan, Dr. Steven R. Fassnacht, Lake Powell pictured at night. ©iStock.com.
and Jeffrey E. Derry
43 The CSU Climate Adaptation Partnership: Colorado Water » June 2021 I
Connecting Research and Policy to Address the Cooperators include the Colorado State Forest Service, the Colorado Climate
Challenges of Living with Climate Change Center, and CSU’s Water Resources Archive.
By Dr. Courtney Schultz, Dr. Leisl Carr Childers, Dr. Niki The contents do not necessarily reflect the views and policies of these agencies,
nor does mention of trade names or commercial products constitute their
vonHedemann, and Tamera Breidenbach
endorsement by the U.S. Government and Colorado State University. CSU is an
equal opportunity university. Colorado Water. Fort Collins, Colo: Colorado Water
Center, Colorado State University, 2021. Print.
Volume 38, Issue 1 Published by Supported by
Colorado Water Center This publication is financed in
Colorado Water is a publication of
Jennifer Gimbel, Interim Director part by the U.S. Department of
the Colorado Water Center. The
Julie Kallenberger, Associate Director the Interior Geological Survey,
newsletter is devoted to highlighting
through the Colorado Water Center
water research and activities at CSU Editor and CSU’s College of Agriculture,
and throughout Colorado. Melissa Mokry Warner College of Natural
Design Resources, Agricultural Experiment
Colorado Water. (2021).
R. Emmett Jordan Station, and Extension.
Colorado Water Center, watercenter.colostate.edu
Colorado State University Production Director
Nancy Grice
Director’s LETTER
W
elcome to “The thing about Reagan is that he was a
our Spring kind person, above all else. He inspired me
edition of the perhaps the most by showing that a person
Colorado Water Cen- with great intellect and authority can also
ter (CoWC) newsletter nurture positive relationships at every level,
focused on climate from undergraduate students all the way
change and adaptation. to the highest levels of state government.
Jennifer Gimbel, JD It has been over five There are many other things to admire about
years since we focused Reagan, such as his tireless work to improve
on climate change and adaptation. Scientists have the Colorado Water Center, his encyclopedic
continued to research and study climate change and knowledge of water literature, and his
its effects. Thanks to the CoWC’s own Brad Udall and enthusiasm for all forms of water research,
his colleagues for all their work and for sharing that he inspired me the most through his humility.
information in this newsletter. His career will be defined by countless
In December’s edition Dr. Reagan Waskom, former successes and achievements, but I believe
Director of the CoWC, eloquently talked about his 34 that the larger legacy he leaves behind is
years at Colorado State University (CSU), including 20 the standard he set for courtesy and respect,
years at the CoWC. He spearheaded the research, edu- whether things were collegial or controversial.
cation, and outreach of water sustainability and created He never wavered from his belief that
a “safe” environment for discussions on many conten- positive relationships are the foundation for a
tious issues in academia, Colorado, and the western successful and happy career.”
water world. I personally respected Reagan for his kind-
—Perry Cabot,
ness, thoughtfulness, insight, and ability to lead difficult
Research Scientist and Extension Specialist
conversations by speaking softly and making quiet sug-
gestions. Most of our readers interacted with Reagan
in his many years of service. One aspect that has not “The thing Reagan taught me most was to
been shared is what Reagan meant to the people who be unwaveringly committed to the objective
worked for him, or as he would say with him. truth. He was very good at cutting through
the fray and getting to the heart of a matter
to analyze the facts in an objective and
unbiased way. And Reagan was fiercely
committed to the facts.”
—Blake Osborne,
Water Resources Specialist-Southern Region
“Reagan was always a trusted source to
throw ideas and thoughts at and always
gave you great responses back as well as
items to think about. If Reagan knew issues
were coming forward, he always made sure
you were in the loop, so there weren’t any
surprises coming at you.”
—Joel Schneekloth,
Water Resource Specialist-Northern Region.
Colorado Water » June 2021 1
Horsetooth Reservoir, ©iStock.com
“It’s challenging to summarize the influence “As I reflect on the days when Reagan was
Reagan’s leadership and mentorship had on my advisor, I realize how crucial his guidance
both my professional and personal growth impacted and empowered my growth as
in only a few sentences. Reagan provided a scientist and as a person. Reagan is a
invaluable support and inspiration throughout generous mentor, passionate to share his
my graduate studies and our work at CoWC. knowledge, and was always willing to share
Like many others, I am the beneficiary of his valuable insights for building a successful
Reagan’s many talents, including his ability to career. I am grateful for his continued support.”
impart his vast water knowledge and shape —Panagiotis (Takis) Oikonomou,
the next generation of water professionals. I Colorado Water Center Affiliate and
am blessed to have worked with one of our Former Civil and Environmental
community’s most respected and committed Engineering Post-Doctoral Researcher
public servants.”
—Julie Kallenberger,
“What was so valuable for me, working
Associate Director
with Reagan, is that not only is he an
“I really valued and respected that no matter extraordinary listener, he has a holistic
how busy Reagan Waskom’s schedule was, perspective to bring to whatever issue is at
he always made time to meet with faculty, hand. Rather than jump to easy answers,
students, and the public. He was happy he was willing to spend some time with
to mentor students and new faculty, and me, probing, looking for underlying
he enjoyed watching them develop their factors, historical significance, and societal
education and research careers.” implications. I miss having his perspective—
and his wisdom.”
—Nancy Grice,
Assistant to the Director —MaryLou Smith,
Former Water Policy and Collaboration Specialist
Reagan’s legacy can be found in every aspect
of CoWC: students, employees, academia, water
users, western water discussions, and finally, in
his vision of a new Western Water Policy Institute
to be part of the SPUR campus in Denver. Thank
you, Reagan. Your influence has given CoWC a
solid foundation to move forward.
Jennifer Gimbel, JD
Interim Director, and Senior Water Policy Scholar,
Colorado Water Center
2 Colorado Water » June 2021
How is Climate Change
Impacting Colorado
River Flow?
Brad Udall, Climate Scientist and Scholar, Colorado Water Center
Dr. Jonathan Overpeck, Samuel A. Graham Dean and Collegiate Professor,
School of Environment and Sustainability, University of Michigan
S
ince the 1970s, scientists have been interested in how runoff in the Col-
orado River Basin (CR Basin) would change as the climate warms. Many of
these studies strongly suggested that the Colorado River (CR) would lose flow
with warming, but in the last few years, scientists have been able to analyze a de-
clining 22-year flow record, the ongoing 2000-2021 “Millennium Drought”. Multiple
studies since 2016 have now found human fingerprints on the nearly 20% loss in
flow since 2000 and attribute up to half of that loss to the approximately 1.2°C or
more warming that has occurred during the last century. This article summarizes
six key peer-reviewed studies related to the topic of CR flow loss. These studies
have found declines in runoff efficiency, investigated the causes of flow loss, and in
some cases made projections about future flow declines based on the 21st-century
climate model projected temperatures.
A high-water mark or “bathtub ring” is visible at Lake Powell, the second largest reservoir on the Colorado River. The
bathtub ring is white because of the leaching of minerals on previously submerged surfaces. ©iStock.com
Colorado Water » June 2021 3
Lake Granby stores Colorado River water and is the largest storage reservoir in the Colorado-Big Thompson Project and the second largest water
body in Colorado. Water is pumped from Lake Granby via the Farr Pump Plant to the Granby Pump Canal, where it flows to Shadow Mountain
Reservoir through a connecting channel to Grand Lake and into the West Portal of the Alva B. Adams Tunnel on its way to users on the east side of the
Continental Divide. ©iStock.com
In 2016, Connie Woodhouse of the can be a major driver of river flow. In tributed about one-third to one-half of
University of Arizona published “In- addition, the paper reported that warm the flow reduction to higher tempera-
creasing Influence of Air Temperatures temperatures exacerbated the modest tures, approximately 1°C over the 20°C
on upper Colorado Streamflow” in Geo- precipitation drought (see Figure 1). average. Using projected tempera-
physical Research Letters. Woodhouse In 2017, Jonathan Overpeck and I tures from climate models, we then de-
and her team found that since 1988, published “The Colorado River Hot termined that by 2050 the river could
flows at Lees Ferry were less than ex- Drought and Implications for the Fu- lose 20% or more, and by 2100 35% or
pected for a given amount of winter ture” in Water Resources Research. more flow solely from temperature in-
precipitation in both high flow and low We found that a lack of precipitation creases. Were these flow decreases to
flow years. They concluded that tem- could not fully explain the 19% CR flow occur with the same precipitation that
perature, in addition to precipitation, loss between 2000 and 2014. We at- occurred from 2000-2014, flow losses
Figure 1. Declining Runoff Efficiency 1906 to 2012. The black line is the difference between the annual Colorado Lees Ferry flow minus
the October to April precipitation, with both measured as percentiles. When the line is above zero, there is anomalously high runoff
relative to the precipitation and when the line is less than zero there is anomalously low runoff relative to the precipitation. Years
marked with green (higher than median flow) and blue (lower than median flow) represent high runoff efficiency years. Years marked
with orange (higher than median flow), and pink (lower than median flow) represent low efficiency years. Note that the high efficiency
years overwhelmingly occurred in the early part of the 20th century and that low efficiency years are almost always after 1988 with
many clustering after 2000. Low efficiency years are characterized by higher March-July temperatures than high efficiency years.
Source: Woodhouse et al. (2016).
4 Colorado Water » June 2021
Lees Ferry. We then re-ran the model
1950s 2000s
50 a − Mead + Powell Volume
Precipitation Temperature removing the increasing temperature
Dominated
Dominated
Drought Drought trend from 1916 to 2014. In this run, the
40
flows increased by about 10% relative
30 to the historic run. By comparing the
maf
20
two runs, we concluded that approx-
imately half of the 20% flow decline
10 was due to warmer temperatures.
Only Lake Mead L. Powell Fills Both Reservoirs
The remaining 10% flow loss was due
25
b − Upper Basin Natural Flows to shifting precipitation patterns from
mountains to deserts.
20
Marty Hoerling of the National Oce-
anic and Atmospheric Administration
maf
15
(NOAA) and other authors from the
10 University of Colorado wrote “Caus-
es of the Century-Long Decline in
5 Colorado River Flow” in the Journal
20 c − Upper Basin Precipitation of Climate in late 2019. Using a so-
phisticated suite of meteorological
18
and hydrological models, this study
16 attempted to calculate the CR tem-
inches
14 perature sensitivity—the flow loss per
12
1°C rise. Their temperature sensitivity
estimates ranged from -2.5% to -6.5%,
10
lower than many similar studies (e.g.,
48
d − Upper Basin Temperatures Udall and Overpeck reported -3% to
46
-10%). They found that of the approx-
imately 20% decline in flow over the
44 last century, about one-half (i.e., 10%)
°F
was due to human-caused climate
42
change. They attributed about one-
40
Annual Data Average Linear Trend Loess Smooth third of the decline (3% of flow) to
1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020 higher temperatures and two-thirds
Figure 2. Critical Colorado River Basin measurements thru end of the Water Year 2020. of the flow loss to precipitation de-
(a). Combined Contents of Lakes Mead and Powell. (b) Upper Basin Natural Flows at Lees clines (7% of flow). This study is in-
Ferry. (c) Upper Basin Precipitation. (d) Upper Basin Temperatures. Note that Lakes Mead teresting in that it is the first study to
and Powell have lost over half of their contents since 2000. River flows are down sharply in
the ongoing Millennium Drought (since 2000). Precipitation is only down slightly, and Upper attribute the slight decline in precipi-
Basin temperatures are up sharply. After Udall and Overpeck (2017), but extended to end of tation (~3%) to human-caused climate
the water year 2020.
change. While the temperature sensi-
tivity is lower than other studies, the
would be 30% and 45%, respectively. In 2018, the well-known University of attribution of precipitation declines
Higher temperatures increase evapo- California, Los Angeles (UCLA) Hydrol- to human causes is concerning be-
ration of all kinds and thus decrease ogist Dennis Lettenmaier, his graduate cause it implies this could continue
water available for the river. Increases student Mu Xiao, and I published “On or get worse. Additional precipitation
in precipitation could alleviate these the Causes of the Declining Colorado declines combined with tempera-
losses somewhat were they to occur. River Flows” in Water Resources Re- ture-induced flow losses would re-
However, climate models do not agree search. This study used a well-known sult in significant flow declines. They
that precipitation will increase (some hydrology model to first generate his- did not attempt to make predictions
have increases, some decreases), and torical flows from 1916 to 2014 using about future changes in flows.
climate theory suggests that storm historic temperature, precipitation, In March of 2020, longtime U.S.
tracks will move northwards, dimin- and wind. The model reliably gener- Geological Survey (USGS) Hydrolo-
ishing precipitation in more southerly ated these flows to within just a few gist Chris Milly and co-author Krista
parts of the CR Basin (see Figure 2). percent of reconstructed gage flows at Dunne published “Colorado River
Colorado Water » June 2021 5
Flow Dwindles as Warming-Driven
Loss of Reflective Snow Energizes
Evaporation” in the nation’s premier
scientific journal, Science. Milly and
Dunne attempted to reconcile differ-
ent published temperature sensitivity
estimates for the CR. Those estimates
range from -2%/°C to -15%/°C. They
created a high-resolution model of the
river and recreated the historic flow of
the river to within a few percent of the
reported natural flow. Experimenting
with many different model parameters,
they determined that the temperature
sensitivity is -9.3%/°C, among the high-
er sensitivities that have been calcu-
lated. Using projected temperature
increases from climate models, they
predicted that flows could drop by
-14% to -31% at mid-century. Including
Figure 3. Small increases in evapotranspiration (all evaporation + all movement of
temperature and precipitation project-
water through plants into the atmosphere) can lead to large declines in river flow.
ed by climate models, their estimates Independent of the total annual precipitation amount, precipitation in the Colorado
widened to +5% to -40%. As to be River each year can be broken into two components: water that leaves the Basin by (1)
evapotranspiration (‘ET’, red) or by (2) river flow (blue). Measured as a percent of total
expected, increases in precipitation precipitation in the Basin, evapotranspiration used approximately 83% of all precipitation
alleviate the losses while declines in- in the Basin in the 1930s (left axis). River flow is the remainder, 17% (right axis). Note that
numbers on the left and right axis add to 100, as they must if precipitation can only turn
crease them. Their key insight is that into either ET or river flow. By 2018, evapotranspiration increases by what seems to be
as snow declines, the darker surface small amount, 3%, to 86% of all precipitation, leaving 14% for river flow (left and right
of the Earth heats up and drives more axis). Most of the increase occurs from 2000 to 2018 during the very warm Millennium
Drought. As measured by the original 1930s amount, river flow is now 3/17 (18%) less than
evapotranspiration, reducing water in the original amount. Seemingly small increases in evapotranspiration (3%) can lead to
the river (see Figure 3). large declines in river flow (18%). Data from Milly and Dunne (2020).
The Colorado River, as photographed from the Desert View viewpoint in Grand Canyon National Park, drains a 246,000 square-mile basin
that includes parts of seven U.S. and two Mexican states. ©iStock.com
6 Colorado Water » June 2021
Figure 4. Summer soil moisture reconstruction for the American Southwest. The red line is a reconstructed 19-year running mean of summer
soil moisture going back to 800 CE, and the blue time series from 1901 to 2018 represents modeled soil moisture. Gray represents the 95%
confidence interval. The 2000-18 mean soil moisture value is the horizontal blue line. The lowest soil moisture periods are represented by
the pink vertical bars. The 2000-18 period is the 2nd worst period in the last 1200 years, second only to the period before 1600 CE. Source:
Williams et al. (2020).
temperatures reduced river flow in
all basins, but the Colorado was the
A key finding is that temperature most affected. A key finding is that
increases in the summer months temperature increases in the sum-
mer months decreased soil moisture
decreased soil moisture immediately, and immediately, and these soil moisture
losses persisted into the following
these soil moisture losses persisted into year, causing flow losses over an ex-
tended period of time.
the following year, causing flow losses How the flow of the CR will change
as the climate warms in the 21st century
over an extended period of time. has been a topic on intense scientific
interest for decades. Since 2016, five
In April of 2020, Park Williams and directed at the CR, has important different studies have attributed up
co-authors published a “Large Con- implications for water managers be- to half of the almost 20% flow decline
tribution from Anthropogenic Warm- cause soil moisture declines have since 2000 to human-caused climate
ing to an Emerging North American been linked to long-term reductions change. An additional study indicated
Megadrought” in Science. Some of in runoff (see Figure 4). that using soil moisture, the 19-year pe-
these authors have previously pub- A study in 2011 by Tapash Das and riod from 2000-2018 was the 2nd driest
lished warnings about how the like- co-authors provided clues as to why in the last 1,200 years. All of these pa-
lihood of megadrought in the South- reduced soil moisture should concern pers were published in well-regarded,
west will increase substantially in water managers and users. “The Im- peer-reviewed scientific journals, includ-
the 21st century as warming occurs, portance of Warm Season Warming to ing two in the nation’s premier journal,
with the chances as high as 80% or Western U.S. Streamflow Changes” in Science. The July to August period in
more by some measures. This study Geophysical Research Letters inves- 2020 in the Four Corners states was the
said that 2000-2018 was the 2nd dri- tigated how increasing temperatures warmest in the last 126 years, according
est 19-year period since 800 AD as would affect the Colorado, Columbia, to the National Weather Service (NWS).
measured by reconstructed July to Northern Sierra, and the Southern Si- This comes on the heels of record-set-
August soil moisture. The drought erra Rivers. Using a hydrology mod- ting temperatures in 2018 in large parts
was caused by both natural variability el that produced streamflow when of Colorado. Warm temperatures from
and humans, with 50% of the cause driven by temperature, precipitation, human causes have already decreased
attributed to higher temperatures. and wind speed, they explored how the flow of the CR, and additional signif-
Without anthropogenic heating and small temperature changes in a single icant losses should be expected as the
drying, the drought would be mod- month affected flows throughout the Earth continues to warm from human
est. This study, while not expressly rest of the year. Changes in summer greenhouse gas emissions.
Colorado Water » June 2021 7
Research Technician Martin Schroeder
(Utah State University) performing routine
maintenance and data collection on eddy
covariance instrumentation in Kremmling,
Colorado. This instrumentation is located in a
field where irrigation has been fully curtailed
for an entire season, in order to perform
intercomparisons with the OpenET ensemble
modeling approach. Professor Larry Hipps and
Professor Alfonso Torres (Utah State University)
collaborate to interpret the data from this
portion of the project.
Evaluating Conserved
Consumptive Use on
High-Elevation
Pastures in the Upper
Colorado Basin
Dr. Perry Cabot, Research Scientist, Colorado Water Center, Colorado
State University Extension and Colorado State University Agricultural
Experiment Station; Aaron Derwingson, Water Projects Director, The Nature
Conservancy; Matt Bromley, Research Scientist, Desert Research Institute
S
ince 2000, the Colorado River The CR Basin states and Congress
Basin (CR Basin) has experi- recently approved a Drought Contin-
enced significant drought con- gency Plan that outlines the actions
ditions and warming temperatures. It that water users will take to address
is estimated that climate change will the threat of declining water supplies
likely reduce flows in the Colorado (CR Drought Contingency Plan Autho-
River (CR) by a range of 5% to 20% rization Act, P.L. 116-14). For the Upper
by 2050 (Udall and Overpeck, 2017). Basin states of Colorado, New Mexico,
Lakes Powell and Mead have also wit- Utah, and Wyoming, this plan includes
nessed declines in the past two de- exploring the feasibility arrangements
cades and are facing historically low that enroll landowners and water
levels. This trend is alarming for an rights holders on a voluntary, tempo-
economic engine as critical as the CR, rary, and compensated basis to reduce
which supplies drinking water to over consumptive water use to leave more
40 million people, irrigates over 5 mil- water in the river. Over the past sev-
lion agricultural acres, and has 4,200 eral years, several high-profile efforts
megawatts of hydropower generating in the Upper Basin have investigated
capacity. It also fuels a multi-billion-dol- how such a program could work ad-
lar recreational economy and supports ministratively and legally to assure
a diversity of wildlife and fish. Without compliance with the CR Compact and
determination and collaborative action improve water security (Grand Valley
to mitigate the impacts of aridification, Water Users Association and J-U-B En-
persistent drought, and the effects of gineers, 2017). Building on the success
a changing climate on the CR Basin, all of these efforts, the Colorado Water
economic sectors are at risk. Conservation Board (CWCB) estab-
8 Colorado Water » June 2021lished workgroups to address addi- serves as vice-chair of the CBRT, who sidered in any future judicial quanti-
tional questions regarding drought advocates a paradigm shift in attitudes. fication of the historical CU (HCU) of
contingency, further educate and in- “Instead of seeing agriculture and new the water rights for a maximum of five
volve stakeholders on water-sharing suburbanites as locked in a zero-sum years out of the ten-year period.
arrangements and promote larger struggle over who gets the West’s di- This project presents a unique op-
statewide discussions. minishing water,” Ms. Snider highlights portunity for researchers from Colora-
In its capacity to direct research and the insistence on collaboration that Mr. do State University (CSU), Utah State
outreach to inform these workgroups, Bruchez advocates, “having spent the University (USU), and OpenET (openet-
the Colorado Basin Roundtable (CBRT) past two decades hatching a series of data.org/) to model evapotranspiration
expressed their need to understand the projects to help ranchers by making (ET)—often used interchangeably with
scientific concerns, measurement and common cause with sportsmen, en- CU in these discussions—over a con-
verification technology, and agronomic vironmental groups and even some siderably large land area subjected to
viability associated with programs that big city water officials and lawyers.” irrigation curtailment. While there are
conserve consumptive use (CU). Irrigat- Encouraged by the broad support for multiple aspects of this project, includ-
This project presents a unique opportunity for researchers from
Colorado State University (CSU), Utah State University (USU),
and OpenET to model evapotranspiration (ET)—often used
interchangeably with CU in these discussions—over a considerably
large land area subjected to irrigation curtailment.
ed pastures, particularly in the higher this research and outreach, a project ing evaluation of impacts on forages
elevation regions of the CR Basin, to evaluate conserved CU (CCU) on subjected to irrigation curtailment,
comprise approximately 80% of total high-elevation pastures was initiated understanding of biomass yields and
irrigated land and consume significant in April 2020 in Grand County, Colora- forage quality relative to CU rates,
amounts of agricultural irrigation water do with funding provided by American carbohydrate and nutrient carryover
in Colorado Water Divisions 4-7 that Rivers, The Nature Conservancy, Trout on stressed pastures, and of course,
ultimately drain to the CR. The CBRT Unlimited, and the CWCB. economic impacts, a primary goal of
agreed that these irrigated pastures the project is the use of remote sens-
represent a dominant source of poten- Research Implementation and ing technology to estimate heteroge-
tially conservable CU, but questions Approach neous ET patterns across the large
still exist regarding the measurability Multiple landowners who operate field sizes common to high-elevation
of actually conserved water, transfer- irrigated parcels throughout Grand irrigated pastures. Participating fields
ability of techniques to other regions, County signed up to support the proj- are characterized by various grasses,
and most importantly, the impacts of ect and were compensated for their forbs, and sedges, as well as differing
reducing CU on the widely recognized participation in the project entitled soil and groundwater, representing
importance of livestock producers that “Evaluating Conserved Consumptive conditions typical to these types of
own this land. While this idea has been Use on High-Elevation Pastures in fields across the Western Slope.
part of the drought contingency portfo- the Upper Colorado Basin.” Irrigation Remote sensing data analysis meth-
lio for decades in some form or anoth- was intentionally cut back on a total of ods have been advocated as an alter-
er, a recent article published in Politico, 1,117.4 acres during the 2020 season, native method for estimating actual
entitled “The Rancher Trying to Solve including 958.7 acres of full-season CU where diversion records are too
the West’s Water Crisis,” captured curtailment (no water applied) and coarse to make estimates at the parcel
what may be recognized as an inflec- 158.7 acres of split-season curtailment scale (URS, 2014). Similarly, empirical
tion point in the development of wa- (irrigation cessation after June 15). The methods (Blaney, Criddle, Hargreaves,
ter-sharing arrangements. In the piece, parcels were also granted SB13-019 Penman-Monteith, 1962) can be used
journalist Annie Snider focuses on the protection status, which provides that to estimate HCU with local weather
leadership of Paul Bruchez, a 5th gen- any decrease in CU resulting from re- data to calculate water balances for
eration rancher, fly-fishing guide who duced irrigation rates will not be con- individual parcels but may not be suf-
Colorado Water » June 2021 9ficiently specific for regional business lite overpass by using the fraction of
transactions and program monitoring reference ET (EToF) values to linearly
The partnership (Cuenca et al., 2013). In some cases, interpolate to a daily timestep.
these methods have exhibited estima-
with OpenET has tion errors in semi-arid, high-altitude Preliminary Results and Analysis
allowed the project environments (Smith, 2008). Further-
more, point-based measurements
The 4-year period of data studied
between 2016-2019 for these fields
to integrate with their obtainable from field sites equipped
with lysimeter, eddy covariance, and
indicated a relatively stable pattern
of annual ET for all sites in previous
intercomparison soil monitoring instrumentation, are years. Not unexpectedly, the sites
very effective but may be too costly to that experienced irrigation curtailment
and accuracy implement for multiple parcels across exhibited a reduction in ET rates for
broad areas (Walter et al., 1990; Carl- 2020. These reductions ranged from a
assessment protocol, son et al., 1991; Tang et al., 2009). The -18.37% to -49.29% change in compar-
importance of improving methods to ison to the baseline average for 2016-
strengthened by evaluate CU is a major impetus behind 2019. This wide range in reduction is
the work of OpenET, which brands it- likely attributable to whether the par-
the installation of self as a platform for “Filling the Big- ticular study site was subjected to a
an eddy covariance gest Data Gap in Water Management.”
Using remotely sensed data for the
full-season or split-season treatment.
The fields used as companion refer-
tower at one of the study area, ET rates were estimated at ences maintained 2020 annual rates
the monthly timescale for years 2016- of ET that were very similar to those
Grand County field 2020, which included the year of the observed in 2016-2019, exhibiting a
irrigation curtailments. The OpenET percent change that ranged between
sites, along with soil platform (openetdata.org/) uses Land- -5.85% and 1.55%.
sat as the primary satellite dataset to It is important to note that at the time
moisture sensing produce an average ET estimate using of this report, the ET data are prelim-
an “ensemble” of four separate and inary in nature, and a larger compre-
instrumentation at diverse ET models: EEMETRIC (Allen hensive report is being developed for
nine locations across et al., 2005; Allen et al., 2007), PT-
JPL (Fisher et al., 2008), SIMS (Melton
review during 2021. The partnership
with OpenET has allowed the project
the study area. et al., 2012; Pereira et al., 2020), and
SSEBop (Senay et al., 2014; Senay et
to integrate with their intercomparison
and accuracy assessment protocol,
al., 2018). The EEMETRIC, PT-JPL, and strengthened by the installation of an
SSEBop models are based on the sur- eddy covariance tower at one of the
face energy balance approach, which Grand County field sites, along with
relies on satellite measurements of soil moisture sensing instrumenta-
surface temperature and surface re- tion at nine locations across the study
flectance combined with other key land area. The intercomparison between
surface and weather variables to esti- field and remote sensing will allow the
mate ET. In contrast, the SIMS model team to perform a valuable “use case
relies on surface reflectance data and study” to test the regional scalability
crop type information to compute ET and transferability of this technique
using a crop coefficient approach for to irrigated pastures under what is
agricultural lands. Reference ET (ETo) expected to be an ongoing challenge
was accounted for using the GridMET of changing climate conditions across
gridded meteorological product (Abat- the Western Slope.
zoglou, 2013) and calculated ETo using
the American Society of Civil Engineers This project is supported with funding
Penman-Montieth equation (Walter, from The Nature Conservancy, Trout
2000). This makes possible a more Unlimited, American Rivers, and the Col-
detailed calculation of daily actual ET orado Water Conservation Board Alter-
in between every 8-day Landsat satel- native Transfer Methods (ATM) program.
10 Colorado Water » June 2021The Agriculture Impact Task Force
©iStock.com
Nora Flynn, Agriculture Water Specialist, Colorado Water Center
T
he Agriculture Impact Task Force (AITF), convened by put together a virtual drought tour. This provided the op-
Governor Polis in June 2020, is a coalition of state, portunity to share 50 stories about agricultural drought in
federal, and agricultural association partners working Colorado and the influences it has for farmers in a virtual
together for the future of agriculture in Colorado. Co-led by format. This platform is readily available to policy mak-
Kate Greenberg, Commissioner of Agriculture, and Megan ers and the general public. To check out the Colorado
Holcomb, Senior Climate Scientist and Interagency Climate drought stories and information visit the following website:
Coordinator at Colorado Water Conservation Board, the bit.ly/3a043qT
AITF’s responsibility is to identify problems and potential Most recently, the AITF created a briefing for the Colora-
threats to agriculture, assess impacts of drought, and coor- do legislative session that highlights recommendations that
dinate across agencies and stakeholders for the greatest precipitated from AITF reflections on important avenues
mutual benefit. for supporting resilience in the agricultural sector. Recom-
One of the first actions of the AITF was to create a com- mendations include providing drought adaptation support,
prehensive list of drought-related financial assistance to mental health resources, and creating market opportunities
ensure producers experiencing challenges due to drought for new and diverse revenue streams. The briefing can be
had a one-stop access point to explore available aid. The found on CWCB’s Agriculture Drought Response webpage
AITF members helped to ensure the distribution of this or at bit.ly/3uBe31z.
resource to producers. A list of drought-related financial The AITF has remained active over the winter of 2020-
assistance programs can be located here: bit.ly/3dI3liY 2021 to prepare for continued drought conditions expect-
Throughout the growing season, members of AITF com- ed during the upcoming growing season. The AITF is also
pile data and information about drought impacts around planning beyond this upcoming season because the effects
the state. In previous years, this information was utilized of drought are widespread across the state, long-lasting,
to coordinate drought tours for state legislators and policy and increasing in severity. The AITF’s efforts in the future
leaders, providing the opportunity for them to witness the will continue to elevate the innovation and resilience of
challenges of drought firsthand. However, this year, due to Colorado’s farmers and ranchers while promoting the many
travel limitations during the COVID-19 pandemic, the AITF benefits agriculture creates for all Coloradans.
Green Mountain Reservoir, located near Kremmling, Colorado on the Blue River has seen reduced water levels due to low snowpack. ©iStock.com
Colorado Water » June 2021 11Embracing Climate Change in
the Colorado Water Plan and
in Local Communities
Russell Sands, Water Supply Planning Section Chief, Colorado Water Conservation Board
C
olorado climate leaders are work- temperatures may rise a 2.5°F to 5°F by Water Center once stated, “climate
ing to guide diverse communities 2050, it is important to remember that change is water change;” and while
and economies toward a resilient the plan also notes that Colorado has climate impacts are broad for Colora-
future by embracing climate action, already warmed 2°F in just the last 30 do, water is certainly on the frontlines
and the Colorado Water Conservation years. This effectively means we are not of the climate discussion. This is why
Board (CWCB) is helping to spearhead just planning for some distant climate fu- the Colorado Water Plan and its 2022
that effort. Adaptive planning is critical to ture—in many ways, the future is here. update will continue to focus on cli-
support a vibrant future, but the CWCB mate challenges and climate-related
or even the state as a whole cannot opportunities for adaptive planning.
do it alone. Meeting our future climate
challenges, which includes climate’s
impact on water, will take leadership at RE
local, state, and regional levels, as well
FU TU
TE R
’S WA
LO RA DO
ON CO
TIN G
BO RA
CO LLA
as public and private involvement. To-
gether, Colorado can work to minimize
future climate risks and recognize new
economic opportunities.
CWCB online Future Avoided Cost Explorer
(FACE) Hazards Tool
Understanding the Cost of Doing
The Colorado Water Plan, which Nothing
uses the same underlying climate A common barrier to climate action is
modeling as the Colorado Climate cost. One way the CWCB is hoping to
Plan, envisions that a much warmer help remove that barrier is by helping
climate may have cascading impacts local planners better make the financial
on cities, farms, streams, and the state case for climate action. In a partnership
as a whole. While climate modeling is with other state agencies and the Fed-
less clear about whether the future eral Emergency Management Agency
will be wetter or dryer, most models (FEMA), the CWCB recently developed
show increasing warming trends, the Future Avoided Cost Explorer
Current Climate Trends and which certainly seems to be playing (FACE) Hazards Tool (cwcb.colorado.
Resilience out. That warming stands to shift the gov/FACE). The tool helps frame-up
This past year was hot and dry—2020 runoff season up further, decrease the sector-specific impacts and provides
was the eighth warmest year and sec- snowpack, and increase the chances future estimated costs from increased
ond, driest calendar year on record, of drought, wildfires, and floods. natural hazards that may result from cli-
trailing only 2002. While the Colorado Brad Udall, Senior Water and Cli- mate change. The result is a tool that
Climate Plan (bit.ly/3amaVz1) projects mate Scientist and Scholar, Colorado puts a cost to inaction, helping local
12 Colorado Water » June 2021Changes in global climate patterns show Colorado faces more frequent and intense natural hazards such as wildfires, droughts, and floods. The
Grizzly Creek fire, above, burned more than 30,000 acres in Glenwood Canyon in 2021. Photo courtesy of the U.S. Forest Service.
communities make the case for why structure, agricultural viability, and While this sounds logical, the discus-
climate action actually pays dividends. seasonal-dependent tourism such as sion is often followed by questions like
At the state level, climate science skiing and rafting. “where do I start?” and “who do I en-
is increasingly leading policy discus- Coupled with steady increases in gage”? Sometimes the answers come
sions and planning resources such as state population means Colorado fac- in learning from other’s stories and part-
guiding frameworks, technical tools, es constant pressure to decide how nering to replicate that success.
and assistance programs. While Col- and where to develop communities. Stories that demonstrate resilience
orado’s climate leaders have made Combined all with other driving fac- in real-time provide exceedingly helpful
great strides in responding to, recov- tors (e.g., economy), Colorado faces lessons in action. When those stories
ering from, and mitigating the impacts increased vulnerabilities. But we can offer local, “neighbor to neighbor” ex-
of hazards, the state’s risk profile will work together to adapt and meet the amples, they also hit home by offering
continue to increase in the coming de- challenge by implementing tangible, actionable priorities with clear behavior
cades. Putting more science, data, and on-the-ground solutions. That work changes attached to them. During the
tools in the hands of local planners starts by highlighting the impacts in 2020-2021 drought, CWCB launched
and community leaders can help build documents like the Colorado Water a “virtual drought tour” where local
a ground-swell of the kinds of actions Plan and supporting and helping fund community members could share their
needed for Colorado to collectively local projects that can build solutions. experience. Those stories were put into
meet its climate challenges. an online story map (bit.ly/3dpqMPc)
Changes in global climate patterns Local Efforts Support Climate Action that allows anyone to look by region at
show Colorado faces more frequent Because resilient systems can respond local stories of impact and resilience.
and intense natural hazards such as to and recover quickly from distur- Some of these stories certainly speak
wildfires, droughts, and floods—each bances, local efforts to build resilience to economic struggle and devastating
with its cascading impacts to water should be focused on minimizing risk climate impacts. But there are also sto-
availability, energy demands, public and increasing preparedness to help ries of creative adaptation, reimagined
health threats, transportation infra- lessen the impacts of future challenges. management, and resilience.
Colorado Water » June 2021 13In both disaster and non-disaster years, water users, at the end of 2022) and the creation of the FACE Hazards
stakeholders, and concerned citizens work tirelessly tool, there are many state documents and tools that collec-
through Colorado’s unique policy engagement structures, tively plot a path forward to greater preparedness. Some
such as the state’s nine basin roundtables and Interbasin examples of recent efforts follow:
Compact Committee—legislatively created water stake- » In January 2021, Colorado set a path towards
holder groups across the state. These groups are commit- ambitious, multi-industry greenhouse gas mitigation
ted to truly adaptive solutions.
(bit.ly/2QdebFZ) solidifying a commitment to climate
Planning for the future means changing how we think,
action and clean air.
resetting expectations, and being increasingly adaptive.
However, planning also needs to be increasingly integrated » The Colorado Energy Office developed a Rebuild and
to maximize benefits, avoid unintended consequences and Re-energize Local Government Toolkit (bit.ly/3efcekm)
work towards greater synergies in planning. to help empower communities with on the ground
examples of innovative programs and policies
throughout Colorado.
Climate Change
» The Colorado Department of Local Affairs’ Resiliency
s
Office updated its Resilience Plan (bit.ly/3gladWK)
ed
ity
Ne Community Ec
on continues to host a climate adaptation webinar series
o
un
(coresiliency.com/webinars) focused on real-time
m
m
ic
om
Vi
topics and actionable advice from communities
eC
br
Economic
an
iqu
around the state.
cy
Un
&
Watersheds
ty &
Dive
& Natural
» The Colorado Department of Public Health and
i
Social Equ
rs
Resources
ity
Colorado Health & Environment is beta-testing the Climate Equity Data
Resiliency Social
Framework Viewer (bit.ly/32oAzPf), which uses data to prioritize
equitable community engagement efforts.
Infrastructure
Housing
Other plans and initiatives include efforts for resilient
ge
Clim
forests (csfs.colostate.edu/forest-action-plan/), resilient
h an
at e
eC
local governments (bit.ly/2RAn7FM), economic transi-
at
Ch
im
an
tion (bit.ly/3dprgF0), renewable energy (bit.ly/32rWgy1),
Cl
ge
Ris rds
ks from
Natural & Other H
aza reimagined infrastructure (bit.ly/2Qzpo3s), regenerative
agriculture (ag.colorado.gov/conservation/soil-health), and
frameworks that address racial equity and economic justice
(bit.ly/3mXwhYP).
An infographic from the the Colorado Department of Local
Affairs’ Resilience Plan illustrsates risks and vulernabuilites in a
Many of these guides expand upon the formative Colo-
holisitic framework. rado Climate Plan, which developed a multi-sector policy
vision to adapt our state to the realities of climate impacts
State Climate Planning is Increasingly Integrated and shifting ecosystem conditions. What made that effort
Since the 2015 Colorado Water Plan, a flurry of climate-in- successful was getting public buy-in through a robust pub-
formed state plans and roadmaps have emerged. Doc- lic process (the Water Plan received 30,000 public com-
uments like The Analysis and Technical Update to the ments) and a commitment to implementation after the Plan
Colorado Water Plan aim to strike a balance between un- was released.
derstanding risk, embracing opportunities, and setting ac- Local project development is essential. Plans and frame-
tionable paths toward increased climate resilience. Climate works can help lead the way, our ability to minimize future
mitigation is the primary approach (i.e., reducing green- climate risks and embrace new economic opportunities
house gas emissions) to prevent the planet from warming largely depends on the collective action of communities
to more extreme temperatures, but climate adaptation is who feel empowered and resourced (financially, technically,
the primary approach to respond to climate impacts and to and in human capacity) to try something new.
build resilience. The reality is both are necessary to meet- As CWCB Director Rebecca Mitchell noted, “Resilient
ing future climate needs. planning must recognize the impacts that are felt across
While CWCB focuses on climate adaptation, staff also our communities and are disproportionately felt in our poor-
work to help to support an array of planning efforts, includ- est communities. Understanding and supporting adaptive
ing a forthcoming climate action hub (climate.colorado.gov). measures that mitigate risk and maximize benefits through
Beyond the Colorado Water Plan update (slated for release projects that support all Coloradans is critical.”
14 Colorado Water » June 2021Colorado River Basin Climate and Hydrology
State of the Science
A Synthesis Report to Support Water Planning and Management
Elizabeth Payton, Water Resources Specialist, Western Water Assessment,
Cooperative Institute for Research in Environmental Sciences, University of Colorado,
Boulder; Jeff Lukas, Principal, Lukas Climate Research and Consulting
Figure 1. Annually averaged temperature for the Colorado River Basin, 1895–2019, shown as
C
departures from a 1970–1999 average. (Data: NOAA NCEI)
olorado River (CR) water man-
agers and water users are fac-
ing the most challenging water The overall goal of the report was to Current Understanding of Basin
supply conditions on record at a time produce a broadly accepted and shared Climate and Hydrology
when CR Basin (Basin) demand has reference that managers, practitioners, The Basin’s hydrology is snow-
risen to where it matches or exceeds and researchers could use to inform melt-driven, and 85% of the annual
the supply. Naturally, those manag- both near-term operations and long- Basin-wide runoff comes from 15%
ers and users are looking for scientif- term planning for an increasingly uncer- of the Basin’s area located in the
ic and technical guidance to navigate tain water supply future, including the mountain headwaters. There is high
the future of the CR, but the vast ar- upcoming renegotiations of the 2007 year-to-year variability in headwaters
ray of complex climate and hydrolo- Interim Guidelines. To that end, the re- precipitation and thus in runoff. Over
gy datasets and models presents its port conveys not only what is currently the past 40 years, there has been a
own challenges. The CR Climate and known and being implemented in each substantial warming trend (2ºF) across
Hydrology Work Group, a consortium area of science and technical practice the Basin (Figure 1). Some important
of major water agencies in the Basin, but also knowledge gaps and opportu- changes in the Basin’s hydrology have
including the Bureau of Reclamation nities in those areas, which in turn also been linked to this warming, including
(Reclamation), Southern Nevada Wa- informs priorities for new research and decreasing spring snowpacks, shifts
ter Authority, Colorado Water Con- research-to-operations activities. to earlier runoff timing, and declin-
servation Board (CWCB), CR District, The report is oriented around the ing runoff efficiency. The most recent
and Denver Water, initiated an effort hydroclimatic knowledge, data, and studies indicate that the warming is
to capture the current state of the modeling that produces inputs to the partly responsible for the cumulative
science and technical practice in a three primary Reclamation operations streamflow deficit since 2000 in the
form that would be more accessible and planning models for the Basin. Be- Upper Basin.
to stakeholders. In 2018, the Work low, we have distilled a brief narrative
Group approached Western Water from three of the main sections of the Primary Data and Models
Assessment (WWA) to develop the report, with the hope of encouraging Guidance for water operations
CR Basin Climate and Hydrology: you to explore these topics at greater and planning in the Basin depends
State of the Science report. length in the full report. on high-quality observations and
Colorado Water » June 2021 15rate across all grid cells, especially at
the highest elevations where observa-
tions are sparse.
Short- and Mid-Term Forecast Tools
Forecasts for the Basin hydrologic
and water system outcomes over the
mid-term (1 month to 2 years) dictate
critical Basin-wide water management
decisions, such as the operating tier in
Reclamation’s Annual Operating Plan.
They also inform individual decisions
by many other water managers and
water users.
Figure 2. The SnowView map tool showing spatial snow-water equivalent (SWE) estimates for The relatively high skill of the sea-
the Colorado River headwaters and portions of adjacent basins for April 1, 2018. The white
sonal streamflow forecasts from NOAA
circles show the individual NRCS SNOTEL sites that are used as the basis for the spatial
estimates. (Source: SnowView, University of Arizona; climate.arizona.edu/snowview/). CR Basin Forecast Center (CBRFC) and
NRCS arises from knowing the water-
shed moisture conditions at the time of
the forecast, i.e., the relative state of the
snowpack and, to a lesser extent, soil
moisture. The quantification of these
watershed moisture conditions has im-
proved and will continue to improve as
remote sensing, and spatial modeling of
snowpack and soil moisture augment
the point observations.
A key source of error in seasonal
streamflow forecasts remains the large
uncertainty in upcoming precipitation
and temperature at timescales beyond
about ten days (Figure 3). Climate fore-
casts for the upcoming month and sea-
son have relatively low skill but are
Figure 3. Schematic of typical forecast skill vs. forecast time horizon for three main types of
weather and climate forecasts. The relatively low skill of sub-seasonal and seasonal forecasts improving, if slowly, and hydrologic
limits their ability to inform streamflow forecasts. (Source: Adapted from a figure by Elisabeth forecasters may use them to “nudge”
Gawthrop and Tony Barnston, International Research Institute for Climate and Society). the seasonal streamflow forecasts in
the near future. The seasonal precipi-
historical records of weather, climate, works are being augmented by remote tation outlooks in the Basin have more
and hydrology variables, including sensing data and spatial modeling, skill in winter and spring and during El
temperature, precipitation, snowpack, filling in gaps in observations in both Niño and La Niña events.
streamflow, soil moisture, and evap- space and time (Figure 2). This en-
oration. The backbone of this obser- hancement provides a more detailed Hydrology Scenarios for Long-Term
vational capacity in the Basin remains view of the Basin’s hydroclimatic vari- Planning
the long-standing, on-the-ground mea- ability and allows more sophisticated To guide long-term water planning at
surement networks, such as the Co- spatial analysis, but it does not lessen the Reclamation and many other water
operative Observer Program (COOP) the importance of the on-the-ground agencies, plausible hydrologic futures
and other weather stations, USGS and networks. These new datasets also put are run through system models to
cooperator streamflow gages, and some additional burden on data users evaluate potential outcomes over the
Natural Resources Conservation Ser- when selecting and interpreting them; next 5 to 50 years. Traditional planning
vice (NRCS) Snow Telemetry (SNOTEL) gridded, spatial climate, and hydrolo- approaches have assumed hydrolog-
snow observing sites. gy products that interpolate between ic stationarity, i.e., that future stream-
Increasingly, data from these net- measurements are not equally accu- flows will have characteristics (e.g.,
16 Colorado Water » June 2021The Colorado River Basin
The Green River pictured in Dinosaur National Monument.
©iStock.com
Colorado Water » June 2021 17Figure 4. Three complementary sources of guidance for long-term basin planning: historical hydrology, paleohydrology, and climate-change
informed hydrology. Annual streamflows for the Colorado River at Lees Ferry, Arizona, representing total Upper Basin natural runoff. (Data:
Historical: Reclamation, usbr.gov/lc/region/g4000/NaturalFlow/; Paleo: Meko et al. 2007, treeflow.info/upper-colorado-basin; Climate change:
Reclamation et al., CMIP5 LOCA, gdo-dcp.ucllnl.org/)
average, variance, extremes) similar due to the impacts of warming. The sin-specific activities are in progress,
to past streamflows; accordingly, the GCM-based future projections indicate and in most cases, Basin water agen-
historical hydrology was the primary a much warmer future that will likely cies and other stakeholders are collab-
basis for planning. impact water supply—smaller spring orating with researchers to carry out
The historically unprecedented snowpacks, earlier runoff, lower sum- studies and implement technical ad-
streamflow deficits of 2000—2004 mer flows, and reduced annual runoff— vances. In other areas, such as climate
pointed to the need to consider addi- and also lead to increased water use by forecasting, progress will also depend
tional sources of guidance. Tree-ring re- crops and urban vegetation. on work by the scientific community
constructions of Basin streamflows ex- well outside of the Basin.
tend the observed natural flow record Challenges and Opportunities Past scientific advances have led to
up to 1,200 years and show a broader A critical aspect of synthesizing the improvements in the various links in the
range of hydrologic variability and ex- current state of the science and tech- chain of data and models, and to more
tremes, including multi-decadal mega- nical practice in the report was identi- accurate and actionable information
droughts. The reconstructed record re- fying persistent knowledge gaps and for decision making. The ongoing ef-
veals that early 20th century high-flow uncertainties, and then describing on- forts documented in the report strongly
years (1905—1930) may have been the going, planned, or potential activities suggest that this progress will continue,
wettest period in 500—1,000 years. and research directions for closing especially at shorter timescales. At lon-
Since the early 2000s, studies using those gaps. ger timescales, the increasing impact of
global climate models (GCMs) to proj- Opportunities to close knowledge climate change means that Basin water
ect the future impacts of human-caused gaps and reduce uncertainties exist planners will have to prepare for climatic
climate change on CR hydrology have across all of the areas of research and and hydrologic futures never seen be-
consistently shown that annual flows technical practice represented in the fore, which is a more difficult challenge
are likely to decline by mid-century report. In many of these areas, Ba- than preparing only for the past.
18 Colorado Water » June 2021You can also read
