CLIMATIC CONTROL ON THE DELIVERY OF FLUVIAL FRESHWATER AND SEDIMENT FROM COASTAL RIVERS OF THE WESTERN UNITED STATES: THE ROLE OF ENSO AND PDO

The rivers draining the coastal ranges along the western coast of the United States vary dramatically in their magnitude of freshwater and sediment delivery. They can all be classified as small mountainous rivers, and therefore react quickly to storm events. The gradient of precipitation ranges from arid rivers (i.e. San Diego) in the south to wet rivers in the north (i.e. Skagit). This range in precipitation leads to a large differences in freshwater and sediment discharge. The annual precipitation determines what role the storm event precipitation plays in the delivery to the coastal ocean. The arid rivers in the south are completely dominated by events, with little to no discharge at other times. While the northern rivers have a higher proportion of non-event rainfall and some may have input from snow melt.

The role of the El Niño Southern Oscillation on storm precipitation, and therefore river discharge, in southern California has been well documented. This study supports the idea that there is positive correlation between warm El Niño years and higher discharges in the southern rivers, and a negative correlation in the higher latitudes. We also report on the role of the Pacific Decadal Oscillation (PDO) on these coastal rivers. There is strong positive correlation between the warm phase of the PDO and increased discharge in the southern rivers, and a negative correlation with the northern rivers. The interaction between these large-scale atmospheric-oceanic cycles and the local climate (arid to wet) determines the fluvial discharge of freshwater and sediment to the coastal ocean.