TreeFlow - St. Vrain River at Lyons, CO

St. Vrain River at Lyons, CO

Calibration & Validation

Long-term Reconstruction

Background

The St. Vrain River is augmented by water from the Colorado-Big Thompson project, operated by the Northern Colorado Water Conservancy District ("Northern"). The City of Longmont is the primary municipal user of water from the St. Vrain. In 2002, Connie Woodhouse developed a tree-ring reconstruction of this gage and several others in Northern's east slope supply, and then in 2004, Woodhouse updated the St. Vrain reconstruction using more recently collected chronologies. The updated reconstruction is shown here. This reconstruction was used for the analyses 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: St. Vrain River at Lyons, CO
USGS Gage: 06724000

Source: Northern Colorado Water Conservancy District and City of Longmont

Adjustment: "Undepleted flow" record, extesively adjusted to account for augmentations and depletions

Observed Flows

Period: 1896-1999

Mean flow:	124 KAF
Median flow:	121 KAF
Minimum:	47 KAF
Maximum:	207 KAF

Reconstructed Flows

Period: 1571-1999

Mean flow:	124 KAF
Median flow:	128 KAF
Minimum:	32 KAF
Maximum:	226 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 tree-ring chronologies from Colorado (both east-slope and west-slope). The residual chronologies, with the low-order autocorrelation removed, were used. Four predictor chronologies were selected by the stepwise procedure for the reconstruction model. Validation statistics were computed using a leave-one-out (cross-validation) approach.

Predictor Chronologies: Pump House (CO), Deer Mountain Update (CO), Big Thompson Update (CO), Hot Sulphur Springs (CO)

Statistic	Calibration	Validation
Explained variance (R2)	0.65
Reduction of Error (RE)		0.61
Standard Error of the Estimate	23,419 AF
Root Mean Square Error (RMSE)		24,259 AF

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

Figure 1. Scatterplot of observed and reconstructed St. Vrain River annual flow, 1896-1999.

Figure 2. Observed (black) and reconstructed (blue) annual St. Vrain River annual flow, 1896-1999. The observed mean is illustrated by the dashed line.

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Long-Term Reconstruction

Figure 3. Reconstructed annual flow for the St. Vrain River (1571-1999) 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 St. Vrain River flow, 1571-1999. 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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