Flood hydrology of the North Platte River headwaters in relation to precipitation variability

SummaryThis paper examines the flood hydrology of the North Platte River headwaters, northern Colorado, in order to provide information for downstream water resource management. The drainage basin (∼3700 km2) is bound on all sides by mountain ranges in excess of 3200 m. As with most high-elevation rivers in the Rocky Mountain region, annual peak floods are generated by spring snowmelt runoff. Analysis of an 89-year continuous record of daily and annual peak discharges (1916–2004) in conjunction with historical climate data reveals statistically significant relationships between hydrologic and climatologic parameters. The magnitude of the annual peak discharge explains 73% of the variability in total annual discharge, with higher predictability for low-flow years than for high-flow years. The peak discharge time series exhibits no temporal auto-correlation in flood magnitude, but does reveal a strong 4–7 year periodicity in inter-annual flood variability. Basin-averaged total precipitation explains 76% of the variability in peak flood magnitude, and 84% of the variability in total annual discharge. Furthermore, both total annual discharge and basin-averaged precipitation are strongly correlated with Palmer Drought Severity Index (PDSI) values at regional scales. The regional PDSI index exhibits a 4–7 year periodicity in wet/dry cycles similar to that of the periodicity in inter-annual flood variability. These results indicate multi-annual, regional climatic conditioning of the total annual discharge regime, while local meteorological conditions during spring snowmelt are responsible for the timing and magnitude of the annual peak flood.