TreeFlow - Willow Creek Reservoir Inflow, CO

Upper Colorado Basin

Willow Creek Reservoir Inflow, CO

Calibration & Validation

Long-term Reconstruction

Background

The Northern Colorado Water Conservancy District ("Northern") operates the Colorado-Big Thompson (C-BT) project, which collects water from the headwaters of the Colorado River and diverts it through the Adams Tunnel for delivery to municipal and agricultural users in northeastern Colorado. Four gages in the Colorado headwaters (Colorado R. near Granby, Fraser R. at Granby, Willow Creek Reservoir inflow, and Blue R. above Green Mountain Reservoir) are used by Northern to monitor and model the west-slope water supply for C-BT. In 2002, Connie Woodhouse generated tree-ring reconstructions of these four gages for Northern as part of the Colorado TreeFlow project. These reconstructions were also used in analyses for Woodhouse and Lukas (2006).

Reference:

Woodhouse, C.A. and J.J. Lukas. 2006. Multi-century tree-ring reconstructions of Colorado streamflow for water resource planning. Climatic Change 78: 293-315.

Metadata

Observed Record

Location: Willow Creek Reservoir Inflow, CO
USGS Gage: 09021000

Source: Northern Colorado Water Conservancy District

Adjustment: "Undepleted flow" record extensively adjusted to account for depletions and diversions

Observed Flows

Period: 1953-1999

Mean flow:	58 KAF
Median flow:	57 KAF
Minimum:	24 KAF
Maximum:	102 KAF

Reconstructed Flows

Period: 1383-1999

Mean flow:	57 KAF
Median flow:	58 KAF
Minimum:	4 KAF
Maximum:	249 KAF

Calibration & Validation

Methods

A forward stepwise regression procedure was used to calibrate the observed flow record with a pool of potential predictors consisting of 25 tree-ring chronologies from western and Colorado. The residual chronologies, with the low-order autocorrelation removed, were used. Three predictor chronologies were selected by the stepwise procedure for the reconstruction model. Validation statistics were computed using a leave-one-out (cross-validation) approach. See Woodhouse and Lukas (2006) for more details.

Predictor Chronologies: Pump House (CO), Green Mountain Res. (CO), Gould Res. (CO)

Statistic	Calibration	Validation
Explained variance (R2)	0.73
Reduction of Error (RE)		0.67
Standard Error of the Estimate	11,594 AF
Root Mean Square Error (RMSE)		12,152 AF

(For explanations of these statistics, see this document (PDF), and also the Reconstruction Case Study page.)

Figure 1. Scatter plot of observed and reconstructed Willow Creek Reservoir annual inflow, 1953-1999.

Figure 2. Observed (black) and reconstructed (blue) annual Willow Creek Reservoir annual inflow, 1953-1999. The observed mean is illustrated by the dashed line.

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Long-Term Reconstruction

Figure 3. Reconstructed annual inflow for Willow Creek Reservoir (1383-1999) is shown in blue. Observed inflow is shown in gray and the long-term reconstructed mean is shown by the dashed line.

Figure 4. The 10-year running mean (plotted on final year) of reconstructed Willow Creek Reservoir inflow, 1383-1999. Reconstructed values are shown in blue and observed values are shown in gray. The long-term reconstructed mean is shown by the dashed line.

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