Cuyamaca
The precipitation gage at Cuyamaca (NOAA co-op station 042239), in San Diego County, is this project’s southernmost site. The gage lies at an elevation of 4640 feet and is situated below Cuyamaca Peak within the Laguna Mountains. Broadly speaking, the gage is reflective of the San Diego River Basin. The precipitation record was obtained from the Historical Climate Data Network for the years 1888-2014.
The reconstruction of water year precipitation at Cuyamaca was generated as part of a project supported by the California Department of Water Resources (CADWR). This project includes reconstructions of water year precipitation (San Gabriel Dam, Lake Arrowhead, Ojai, and Cuyamaca) and streamflow (Arroyo Seco and Santa Ana River) for southern California and the Kern River in the southern Sierras. This set of reconstructions was developed by Dave Meko, Erica Bigio, and Connie Woodhouse in 2017, based on updated and new collections of tree-ring data in California sampled for this project.
Methods
Total water year (October-September) precipitation at Cuyamaca was reconstructed using a two-stage regression procedure. Tree-growth at each site was first converted into an estimate of precipitation by stepwise regression of precipitation using tree-ring width indices, from the current year and lagged one year, as predictors. Squared terms on the tree-ring predictors were also included in the regression to allow for possible curvature in relationships between tree-growth and precipitation. In the second step, the gage reconstruction was generated by averaging an appropriate set of single site reconstructions. Final estimates of precipitation were interpolated from a piecewise-linear smoothed scatter plot of the observed precipitation values and the precipitation estimates averaged over the individual tree-ring sites. The procedure was repeated for subsets of tree-ring chronologies with different periods of common time coverage to build a “most-skillful” reconstruction, starting in the early 1400s, and a “longest” reconstruction, starting in the early 1100s. Details of the reconstruction method can be found here.
| Statistic | Most Skillful: Calibration | Most Skillful: Validation | Longest Model: Calibration | Longest Model: Validation |
| Explained variance (R2) | 0.54 | 0.43 | ||
| Reduction of Error (RE) | 0.57 | 0.38 | ||
| Standard Error of the Estimate | 8.682 in. | 10.211 in. | ||
| Root Mean Square Error (RMSE) | 8.936 in. | 10.703 in. |
Note: The statistics listed in the table represent average accuracy, while the reconstruction method yields error bars that vary in width over time -- generally wider for wet years than for dry years. The listed statistic R2, the decimal proportion of variance explained by the reconstruction in the calibration period, is computed directly from the reconstruction residuals. For an explanation of these statistics, see this document.
Figure 1. Scatter plot of observed and reconstructed Cuyamaca annual precipitation, 1888-2014. Note that the R2 value here is slightly different than in the table. The table R2 value is the average explained variance from the three models that make up the most skillful reconstruction. The value in the scatter plot reflects the explained variance for the two models that cover the instrumental period (more details).
Figure 2. Observed (gray) 1888-2014, and reconstructed (blue) 1850-2016, Cuyamaca annual precipitation. The observed mean is illustrated by the black dashed line.
Figure 3. Reconstructed annual precipitation for the Cuyamaca annual precipitation (1404-2016) is shown in blue. Observed flow is shown in gray and the long-term reconstructed mean is shown by the black dashed line.
Figure 4. The 10-year running mean (plotted on final year) of reconstructed annual Cuyamaca precipitation, 1404-2016. Reconstructed values are shown in blue and observed values are shown in gray. The long-term reconstructed mean is shown by the black dashed line.
Figure 5. Scatter plot of observed and reconstructed Cuyamaca annual precipitation, 1888-2014 (more details).
Figure 6. Observed (gray) 1888-2014, and reconstructed (blue) 1850-2016, Cuyamaca annual precipitation. The observed mean is illustrated by the black dashed line.
Figure 7. Reconstructed annual precipitation for Cuyamaca (1126-2015) is shown in blue. Observed flow is shown in gray and the long-term reconstructed mean is shown by black dashed line.
Figure 8. The 10-year running mean (plotted on final year) of reconstructed Cuyamaca annual precipitation, 1126-2015. Reconstructed values are shown in blue and observed values are shown in gray. The long-term reconstructed mean is shown by the black dashed line.
