Regionalization and Reconstruction of Snow Water Equivalent in the Upper Colorado River Basin
This study focuses on regionalization and reconstruction of April 1 snow water equivalent (SWE) of snow courses stations located in the Upper Colorado River basin (UCRB) and evaluates regional drought scenarios for the last 480 years. Rotated principal component analysis (PCA) and cluster analysis were used to regionalize the snow course stations in the UCRB. Both methods of regionalization identified four regions of snow course stations, which were spatially distributed in the regions (east, west, north and south). Then, partial least squares regression (PLSR) was used to reconstruct three regional SWE time series in the UCRB based on residual tree-ring chronologies. Tree-ring chronologies that were positively and negatively correlated with higher than 95% confidence levels (based on the absolute value of correlation with the regional composite April 1 SWE) were screened and retained as a pool of predictors. The PLSR reconstruction model was developed using all the ranked chronologies available in the pool of predictors, and then sequentially the least correlated predictor was removed and PLSR was rerun. This process was continued until an optimal performance was obtained. In addition to the regional composite April 1 SWE reconstruction, individual April 1 SWE stations with the highest loading from each principal component were also reconstructed in order to compare the performance. The regional reconstruction of SWE had better statistical performance as compared to the individual station’s reconstruction. The spatial and temporal variability of drought was evaluated based on the duration as identified by the 3-year, 5-year and 10-year moving average of three reconstructed regional composite time series of April 1 SWE. Finally, the drought duration from SWE was compared with the drought duration based on three reconstructed water year stream flow each from the identified regions. The results indicate the average drought duration in the basin was 3–14 years depending upon the variables (April 1 SWE and water year stream flow) and the moving average considered.