Pacific Northwest

Introduction

The Pacific Northwest hydrologic unit is largely comprised of the US portion of the Columbia River basin, plus the rivers which drain the coastal ranges of Oregon and Washington. The Columbia is the second-largest river in the US in mean annual discharge, and along with major tributaries such as the Snake River, it supports extensive irrigated agriculture, the largest hydropower resource in the US, and important but threatened salmonid fisheries.

Because of the tremendous climatological diversity across the Columbia River basin, reconstructing streamflow for the mainstem Columbia presents greater challenges than other basins, such as the Sacramento River or upper Colorado River, which have more homogeneous climates. In addition, trees in the northern tier of states in the western US have moisture signals which can be weaker and more seasonally complex than their counterparts further south.

Status of Reconstruction Efforts

In 2004, Gedalof et al. published a reconstruction of annual streamflow for the Columbia River at The Dalles, OR, which used previously collected chronologies primarily from the lower part of the basin. This reconstruction explained only 35% of the variance in the observed flow record, but was a good first step towards more robust reconstructions for the basin.

A NOAA-funded project led by Jeremy Littell of the University of Washington Climate Impacts Group is currently re-evaluating existing chronolologies and making new field collections to update and bolster the tree-ring network in the basin. Their preliminary calibration for The Dalles explains 57% of the variance in observed flow, so the prospects for high-quality reconstructions of the Columbia River and its main tributaries look good. This work should be completed in 2010.

Meanwhile, Erika Wise at the University of Arizona's Laboratory of Tree-Ring Research has been developing new chronologies and reconstructing streamflow for the upper Snake River. This work has just been completed (June 2009) and the data will be archived here at TreeFlow in 2010.

Workshops

One workshop for water managers and stakeholders have been held in the Pacific Northwest, in Spokane, WA, in May 2008. Click on the workshop below to access a summary report and the presentations; see the Treeflow Workshops page for general information about the series of workshops across the western US.

• Spokane, WA - May 2008

 

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Applications

There are many different ways to use tree-ring reconstructions in the planning and management for water resources, from educational tools to inform stakeholders about the occurrence of severe droughts, to numerical input into water supply models to test the resilience of the system under past hydrologic conditions.

In the Pacific Northwest, applications to water management have been limited by the data available. The range of entities represented at the Spokane workshop indicates is encouraging and suggests widespread interest. Once more data becomes available, we expect water resource applications to soon follow, given the planning challenges posed by regional warming and reduced snowpacks.

See the TreeFlow Applications page for summaries of other applications of tree-ring data around the West.

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