TreeFlow - Williams Fork near Leal, CO

Upper Colorado Basin

Williams Fork near Leal, CO

Calibration & Verification

Long-term Reconstruction

Background

The Williams Fork near Leal gage measures a key component of Denver Water's water supply. A reconstruction for this gage was first developed by Connie Woodhouse in 2002, and then re-calibrated in 2004 using new tree-ring chronologies that end in 2002. The 2004 re-calibration is shown below. This reconstruction was used in analyses described in 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: Williams Fork near Leal, CO
USGS Gage: 09036000

Source: Denver Water

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

Observed Flows

Period: 1916-2002

Mean flow:	79 KAF
Median flow:	76 KAF
Minimum:	34 KAF
Maximum:	130 KAF

Reconstructed Flows

Period: 1437-2002

Mean flow:	76 KAF
Median flow:	78 KAF
Minimum:	24 KAF
Maximum:	123 KAF

Calibration & Verification

Methods

A forward stepwise regression procedure was used to calibrate the observed flow record with a pool of potential predictors consisting of ~30 tree-ring chronologies from Colorado). The residual chronologies, with the low-order autocorrelation removed, were used. Four predictor chronologies were selected by the stepwise procedure for the reconstruction model for the Williams Fork near Leal. Validation statistics were computed using a leave-one-out (cross-validation) approach. Further details are provided in Woodhouse and Lukas (2006).

Predictor Chronologies: Dillon (CO), Gould Reservoir (CO), Pump House (CO), Princeton Douglas-fir (CO)

Statistic	Calibration	Validation
Explained variance (R2)	0.67
Reduction of Error (RE)		0.62
Standard Error of the Estimate	11,644 AF
Root Mean Square Error (RMSE)		12,010 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 Williams Fork annual flow, 1916-2002.

Figure 2. Observed (black) and reconstructed (blue) annual Williams Fork annual flow, 1916-2002. The observed mean is illustrated by the dashed line.

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Long-Term Reconstruction

Figure 3. Reconstructed annual flow for the Williams Fork (1383-2002) is shown in blue. Observed flow 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 Williams Fork flow, 1383-2002. 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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