ENSO and Pacific Decadal Oscillation: their effects on basins of the Puget Sound estuary

Abstract

Puget Sound in Washington state is one of the largest estuaries in the world and is home to abundant and diverse wildlife and urban communities alike. The different basins of its more 1000 square miles respond uniquely to global climate oscillation patterns like the El Nino Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). In order to better understand just how quickly and each of the four basins of the Sound respond to these natural patterns, we investigated the relationships between seasonal rainfall and river discharge averages and the indexes that rate the strength of these global weather oscillations. We found there to be very little correlation between the oscillation indexes and rainfall anywhere in the Puget Sound. River discharge rates in the Main and South Basins, which are home to the cities of Seattle and Tacoma, tended to lag behind ENSO and PDO by one to two seasons. The strongest relationships here were between late fall indexes and springtime river discharge. The oscillations were shown to explain nearly half of the seasonal variation in river discharge in these areas. The Whidbey Basin discharge rates took two to three seasons to respond to the indexes and the Hood Basin saw little to no correlation. It was also discovered that averaging the ENSO and PDO indexes into one rating produced a higher correlation for river discharge in all basins but Hood. This knowledge could help to improve our ability to predict changes in snowpack, salinity and other aspects related to freshwater mixing throughout the estuary further in advance.