Denver Water
Tree-Ring reconstructions being used:
South Platte River at South Platte (1634-2002), Colorado River
at Kremmling (1440-2002)
Description of application:
Denver Water has used the flow reconstructions to help model the
yield of their system under a broader range of conditions than those
seen in their 45-year model period (1947-1991). Denver Water took
the annual flow values reconstructed from the tree rings, then used
a “model year-analog” method to derive a plausible daily hydrology
for these years. For example, if the reconstructed annual flow value
for 1717 was closest to that for 1951, among the 45 model years,
then the daily hydrology for 1951 was used for 1717. If a reconstructed
year (like 1685) was beyond the range of the model period, then
the daily hydrology for the closest gage year (2002) was scaled
up or down to match the reconstructed annual flow. Then, the daily
flows were input into a modified version of their water supply model,
PACSM (Platte and Colorado Simulation Model). PACSM was then used
to simulate the entire period (1634-2005) using the tree-ring data
(1634-1946) and gage data (1947-2005), to determine what level of
demand could be met through all years, and determine what level
of demand could be met during various dry sequences. The modeling
results indicated that the reconstructed drought of 1845-1848 (critical
period: summer 1844-spring 1848) would cause Denver Water to deplete
its storage down to its strategic reserve, even with the progressive
application of water use restrictions. This is a greater depletion
than was produced in the same modeling run by either the recent
2000-2004 drought, or the 1953-1956 drought (critical period: summer
1953-spring 1957), which is the design drought for Denver Water.
Presentation: Denver
Water’s use of tree ring-based stream flow reconstructions in
water resources management - Steve Schmitzer, Denver Water (Boulder,
CO, May 9, 2006)
Contact Person:
Steve Schmitzer, steve.schmitzer@denverwater.org
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City of Boulder
with AMEC Earth & Environmental (formerly Hydrosphere Resource
Consultants) and Stratus Consulting
Tree-Ring reconstructions used:
Boulder Creek at Orodell (1703-1987), Boulder Creek at Orodell
(1566-2002), Platte Basin Climate Division summer temperature (NE
Colorado; 1566-1983)
Description of applications:
With Hydrosphere Resource Consultants, the City of Boulder developed
a Drought Plan to identify impending droughts and respond with appropriate
management strategies. The Drought Plan was based on an analysis
of the climatic and hydrologic aspects of droughts that have affected
Boulder’s water supply, which mainly comes from the Boulder Creek
watershed, with the rest coming from the upper Colorado River watershed.
The 95-year gaged record of streamflow was extended using a 300-year
tree-ring reconstruction of Boulder Creek annual streamflow. The
reconstructed flows were then run through a model of Boulder’s
water supply system to test the effectiveness of various combinations
of drought recognition triggers and drought response strategies
over the 300 years of tree-ring based hydrology. As the Drought
Plan was being completed, extreme drought conditions were unfolding,
resulting in record-low streamflows in 2002. The Drought Plan allowed
Boulder to respond effectively to this drought.
This work for the Drought Plan was built on for a recently completed
(2009) study led by Stratus Consulting, along with Hydrosphere and
scientists from the University of Colorado and NOAA, with funding
from the NOAA Climate Program Office - Sector Program. Updated reconstructions
of streamflow for Boulder Creek and summer temperature for northeast
Colorado were generated specifically for this project. Using a non-parametric
k-nearest-neighbor technique, monthly temperatures, monthly precipitation,
and gaged streamflow from instrumental record (1953-2002) are resampled
to produce simulated streamflows for 1566-2002, with corresponding
monthly temperature and precipitation, that are conditioned on the
tree-ring-reconstructed streamflows. Essentially, this process disaggregates
the paleo streamflows into estimated climatic variables (monthly
precipitation and temperature) so that those variables can be manipulated
independently. The simulated monthly temperature and precipitation
are then input into a snowmelt-runoff (SRM) and water-balance (WATBAL)
model to produce modeled Boulder Creek flows. Then changes in temperature
and precipitation forecasted from climate models are combined with
the paleodata to produce simulations of past hydrology under plausible
future climate conditions. This approach allows water managers to
assess the joint risks of climate variability (as more fully seen
in the paleorecord) and climate change, by examining what would
happen if the droughts of the past occurred again under warmer and
potentially drier conditions.
For more information on this second application, see: Expanding
the Tool Kit for Water Management in an Uncertain Climate -
Southwest Hydrology, Jan/Feb 2007; and the final report (February
2009) by Stratus Consulting: The
Potential Consequences of Climate Change for Boulder Colorado’s
Water Supplies.
Contacts: Lee Rozaklis, lee.rozaklis@amec.com;
Joel Smith, jsmith@stratusconsulting.com
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U.S. Bureau of Reclamation
– Aspinall Unit (Gunnison River, CO)
Tree-Ring reconstructions used:
Gunnison River at Crystal Reservoir (1569-1997)
Description of application:
The US Bureau of Reclamation’s Aspinall Unit (Gunnison Basin,
Colorado) is preparing
an EIS for its operations to support endangered fish recovery
in the Gunnison River and its tributaries. As with the Bureau’s
EIS process in the Lower Colorado, there has been an effort to use
“alternative hydrologies”, specifically tree-ring data, in the
assessment of different management alternatives. The strategy for
applying the tree-ring data is very similar to that described for
the Lower Colorado: the 429-year tree ring reconstruction is bootstrap-resampled
in 30-year blocks, then system state information (three states in
this case: dry-normal-wet) is extracted from the tree-ring data,
and then flow magnitudes taken from the observed record (1937-1997)
are probabilistically assigned to each paleo-state using a non-parametric
k-nearest-neighbor technique. This creates a rich variety
of 30-year sequences with “paleo-conditioned” flows. Then a
sequent peak algorithm can be used to determine the storage required
to meet various yields, given a particular drought deficit associated
with a flow sequence. The results from the paleo-conditioned data
can then be compared to those derived from the observed flow record.
Unfortunately, a judicial decision in 2008 to fast-track the EIS
meant that these tree-ring analyses were not used in the EIS.
Presentation: Progress
on use of paleo-conditioned streamflow data on Gunnison River basin
for Aspinall EIS - Chris Cutler, U.S. Bureau of Reclamation
(Tucson, AZ, Nov. 1, 2006)
Contact Person:
Chris Cutler, ccutler@uc.usbr.gov
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Salt River Project
Tree-ring reconstructions used:
Colorado River at Lees Ferry (1521-1964), Salt-Verde-Tonto (1521-1964
and 1200-1964)
Description of application:
A joint
research project between Salt River Project (SRP) and the University
of Arizona’s Laboratory of Tree-Ring Research (LTRR) investigated
how often droughts occurred simultaneously in the Upper Colorado
River basin and the Salt-Verde-Tonto River basin, both of which
supply water to SRP. Reliable tree-ring reconstructions of streamflow
back to 1521 were developed by LTRR for both basins, and it was
found that extreme flows (high and low) in both basins are strongly
synchronous, and that it was rare for one basin to have high flows
when the other had low flows. The Upper Colorado basin, then, is
not a reliable buffer for shortages in the Salt-Tonto-Verde basin.
It was also found that synchronous low flow years tended to cluster
in time, which would heighten water stress on SRP.
Further examination of the Salt-Verde-Tonto flow reconstruction
(back to 1200) showed that there were eight droughts in the past
800 years that were at least as severe as the 1950s design drought
(six years) and the current (1995- ) drought. One drought, from
1575-1585 (11 years), was clearly more severe than either of these.
A simple model of SRP’s current water allotment and groundwater
pumping scenario was run using the reconstructed flows for 1575-1585
as inputs. This modeling showed that SRP’s storage would be fully
depleted in the last year of this 11-year drought. A slight modification
to the pumping/allotment scenario resulted in some storage being
retained through the drought. Thus, the tree-ring data can be used
to test the robustness of the SRP system, under different policies,
to droughts worse than seen in the gaged record.
A second stage of the SRP-LTRR project is ongoing, with new tree-ring
collections to update the Salt-Verde-Tonto flow reconstructions
through 2005, allowing direct comparison of paleodroughts with the
most recent drought. The updated collections will also include separate
measurements of early- and late-season tree growth too see whether
seasonal information useful to water managers can be extracted from
the tree-ring data. SRP expects to once again examine its water
allocation and drought planning process using the results of this
extended chronology.
Presentation: Application
of tree-ring research results - Salt River Project - Charlie Ester,
Salt River Project (Tucson, AZ, Nov. 1, 2006)
Contact person:
Charlie Ester, ceester@srpnet.com
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U.S. Bureau of Reclamation
- Lower Colorado
Tree-ring reconstructions used:
Colorado River at Lees Ferry, AZ (1490-1997); Colorado River at
Lees Ferry, AZ (762-2005)
Description of application:
The USBR wanted to employ what they call "alternative hydrologies"
(i.e., providing flow information beyond that in the gaged record)
for modeling that would support the
development of shortage criteria and coordinated operations for
Lake Powell and Lake Mead, for an EIS that was completed in
fall 2007. Tree-ring reconstructions were an obvious choice for
this purpose, but stakeholders had expressed concern about the accuracy
of the tree-ring data in estimating flow magnitudes, particularly
during extreme droughts. Analysis of several different tree-ring
reconstructions of flow at Lees Ferry showed that while the reconstructions
sometimes differed considerably in their estimation of specific
annual flows, the reconstructed system "state"--whether
the flows were above or below average--was very similar among the
reconstructions.
Thus, the USBR devised a novel method in which the system state
information was extracted from the tree-ring record, but the specific
flow magnitude assigned to the system state in a given year was
taken from observed flow record. In greater technical detail: First,
a non-homogeneous Markov model with a kernel estimator was applied
to the tree-ring record, generating a 60-year sequence of system
state (e.g., wet-dry-dry-dry-wet-dry-dry-wet-wet-etc.). Then, a
non-parametric k-nearest-neighbor technique was used to
conditionally resample years from the observed record, to assign
annual flow values to the state sequences. This process was repeated
500 times, generating 500 60-year simulations. The resulting "paleo-conditioned"
flow simulations encompassed a rich variety of streamflow sequences
(droughts and wet periods), including sequences not seen in the
observed record. For example, more than half of the 500 simulations
had droughts that were longer than the longest drought (5 years)
in the observed record.
In preparation for further modeling, the paleo-conditioned annual
flows were then temporally disaggregated into monthly flows, and
spatially disaggregated from one node (Lees Ferry) into 29 nodes,
using a new non-parametric disaggregation technique. The disaggregated
monthly flows were input into CRSS (Colorado River Simulation System)
the USBR's long-term basin planning model. Multiple simulations
of the CRSS with the paleo-conditioned flows showed, not surprisingly,
greater probability of system shortages than when CRSS was run with
flow simulations resampled (using the index sequential method) from
the observed record.
The analyses described above appear in Appendix N of the Final
EIS.
Presentation: Stochastic
Nonparametric Framework for Basin Wide Streamflow and Salinity Modeling:
Application to Colorado River basin, Jim Prairie, USBR (Boulder,
CO, November 10, 2006).
For other resources about this application, see Jim Prairie's personal
web page.
Contact Person:
Jim Prairie, jprairie@uc.usbr.gov
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