TreeFlow - South Platte River below Cheesman Lake, CO

South Platte River below Cheesman Lake, CO

Calibration & Validation

Long-term Reconstruction

Background

The South Platte River is the primary water supply for the Denver metro area (Denver Water). The gage above Cheesman Lake is upstream of most augmentation from west-slope diversions and represents the flows from upper basin of the mainstem South Platte. In 2002, Connie Woodhouse developed a tree-ring reconstruction of this gage, which extends only through 1987 because key predictor chronologies available at that time ended in that year. Given the chronologies currently available, this reconstruction could be re-calibrated and extended through 2002. This reconstruction appears in 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: South Platte River below Cheesman Lake, CO
USGS Gage: 06701500

Source: Denver Water

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

Observed Flows

Period: 1916-1987

Mean flow:	163 KAF
Median flow:	152 KAF
Minimum:	60 KAF
Maximum:	393 KAF

Reconstructed Flows

Period: 1685-1987

Mean flow:	159 KAF
Median flow:	157 KAF
Minimum:	23 KAF
Maximum:	293 KAF

Calibration & Validation

Methods

A forward stepwise regression procedure was used to calibrate the observed flows 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. For further details and analyses, see Woodhouse and Lukas (2006).

Predictor Chronologies: Van Bibber (CO), Turkey Creek (CO), Dillon (CO), Cathedral Creek (CO)

Statistic	Calibration	Validation
Explained variance (R2)	0.63
Reduction of Error (RE)		0.58
Standard Error of the Estimate	44,767 AF
Root Mean Square Error (RMSE)		46,021 AF

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

Figure 1. Scatterplot of observed and reconstructed South Platte River annual flow, 1916-1987.

Figure 2. Observed (black) and reconstructed (blue) annual South Platte River annual flow, 1916-1987. The observed mean is illustrated by the dashed line.

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Long-Term Reconstruction

Figure 3. Reconstructed annual flow for the South Platte River (1685-1987) 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 South Platte River flow, 1685-1987. 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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