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W05415 WOODHOUSE ET AL.: UPDATED COLORADO RIVER RECONSTRUCTIONS W05415 ~ 5000 CJ ~ 3000 ~ o ii: 1 000 1650 1700 1750 1800 1850 1900 1950 2000 1550 1600 3500 ~ ~ 3000 ~ 2500 ii: 2000 1500 1550 1600 1650 1700 1750 1800 1850 1900 1950 2000 Year Figure 3. San Juan near Bluff, Utah, reconstructed streamflow, 1569-1997, from two models, full predictor pool (gray lines) and watershed-limited predictor pool (black lines): (top) annual values and (bottom) lO-year running average. 3.3. Sensitivity of the Lees Ferry Reconstruction to Modeling Approaches [15] Reconstructions of Lees Ferry streamflow were tested using four different forms of the predictor tree ring data: residual chronologies (Lees-A, described in section 3.1), standard chronologies (Lees-B), principal components of residual chronologies (Lees-C), and principal components of standard chronologies (Lees-D). Exploratory analysis suggested 1490 as a reasonable start year for the reconstruc- tions; of the original 62 chronologies, 31 residual chronolo- gies and 30 standard showed significant correlations with annual streamflow and passed the screening test for time coverage to at least 1490 (Table 2). Stepwise regression on the standard chronologies (Table 2, Lees-B) yielded a recon- struction model with the same number of predictors (7) as for the residual chronology version, and a slight increase in F level and variance explained by regression (see Figure 1 for locations of predictor chronologies and Supplementary Data 2 for regression coefficients). [16] The PCA indicated that the residual chronologies have somewhat more spatial structure than the standard chronologies (Supplementary Data 3, http://www.ncdc.noaa. gov /pa 1 eo/pub s/woodhouse2006/woodhouse2 006. h tml). PC 1 is by far the most important component, accounting for 47% of the variance of the residual chronologies and 45% of the variance of the standard chronologies. For both sets of data, five PCs have eigenvalues exceeding 1.0, and these PCs account for a cumulative 69% (residual chro- nologies) and 68% (standard chronologies) of the tree ring vanance. [\7] PC loadings on an chronologies are positive for PC 1 whether the PCA is on residual or standard chronologies. This pattern attests to the strong overriding common signal in tree growth over the Upper Colorado Basin. There appears to be some species dependence, with highest weights on Pinus edulis chronologies. Spatial organization in PCs 2-5 is most obvious for the residual chronologies: maps ofloadings (not shown) indicate an east-west contrast in PC 2, a north-south contrast in PC 3, and spatial clustering in PCs 4 and 5. [18] The predictor pools, based on significant correlation of PCs with streamflow, were PCs l, 15 and 16 for the residual chronologies, and PCs 1, 17, 28, and 29 for the standard chronologies. Except for PC 1, a high percentage of tree ring variance accounted for by a PC did not imply strong correlation with streamflow. Table 3. Statistics of Observed and Reconstructed Flow of Colorado River at Lees Ferl)' for 1906-1995 Calibration Period Running Means as Percentage of Normal" Statisticsb Lowest Highest Series" Mean SO Skew r(1) I year 5 years 20 years 1 year 5 years 20 years Lees-A 18778 4787 -0.14 0.04 31 79 89 157 139 III Lees-B 18778 4885 -0.26 0.22 28 76 83 151 142 115 Lees-C 18778 4526 -0.52 ~0.05 25 81 90 141 130 108 Lees-O 18778 4679 -0.47 OJI 28 73 83 148 139 115 Obs. 18778 5332 0.15 0.25 37 72 85 166 145 116 _ "Lees-A is reconstruction from residual chronologies, Lees-B is from standard chronologies, Lees-C is from PCs of residual chronologies, and Lees-D is trom pes. of standard chronologies. Obs is the observed natural flow record (see text). :Stal1StlCS are mean and standard deviation in MCM. skewness, lag I autocorrelation. Normal IS defined as mean of observed flows for calibration period 1906-1995. 5 of 16