Quantification of linkages between large-scale climatic patterns and precipitation in the Colorado River Basin

This study analyzed the linkages between large-scale climate patterns and regional precipitation variability, in particular the interannual variation of seasonal precipitation in the Colorado River Basin. Two climate indices, the Southern Oscillation Index (SOI) and the Pacific Decadal Oscillation (PDO), were selected to represent climate patterns. Conceptual influence indices, which quantify the strength of linkages between climate patterns and precipitation variability, were developed based on the Standardized Precipitation Index (SPI). In turn, the spatial variability of the influence indices within the Colorado River Basin was examined for different combinations of SOI and PDO phases and lead times from zero to three seasons. Precipitation in two seasons (winter and summer) significantly responded to the El Niño-Southern Oscillation (ENSO) phases by decreasing winter precipitation in the lower basin (to high ENSO phase) and by increasing summer precipitation in the upper basin (to low ENSO phase). The PDO phase enhanced those relationships both in intensity and frequency. The overall results of this study revealed that the precipitation of the Colorado River Basin was significantly influenced by climate fluctuation phases.