Improving Estimates of Hydrologic Extremes:

Applications to the Olympic National Forest

Ingrid TohverPNW Climate Science Conference September 14, 2011Seattle, WA

Partnerships with Stakeholders

Olympic National Forest and Park:

Kathleen O’Halloran

Luis Santoyo

Bill Shelmerdine

Robert Metzger

Robin Stoddard

Climate Impacts Group &

Civil and Environmental Engineering,

University of Washington:

Alan Hamlet

Se-Yeun Lee

Ingrid Tohver

Robert Norheim

Project Premise

• Assess potential impacts of climate change on federal lands and incorporate projections into management practices

• Update estimates of extreme streamflows

• Support protection of fish and wildlife habitat

• Support road maintenance and flood control infrastructure

Photos courtesy of Olympic National Park

USGS Streamstats Tool

Web-based GIS tool used to estimate streamflow statistics:

Inputs = basin size, annual precipitation and elevation

• DEM & PRISM datasets

Regression equation developed by USGS calculates statistics

http://water.usgs.gov/osw/streamstats/

Climatic caveats:

• Unchanging mean annual precipitation

• Seasonality is lost in calculation

Climate Change Scenarios for the PNW

Figures’ source: Mote and Salathé 2010

Temperatures warm across all projections

Mean annual precipitation projections do not show a clear trend

Seasonal signal of precipitation shifts is lost in the annual projections

Contrasting Hydrologic Models

Physically-based VIC Model

Explicitly integrates climate conditions

Applies future T & P projections to estimate daily runoff at each grid cell

Daily runoff used to estimate shifts in extreme streamflowfrequency

Spatial resolution:

Fine - 1/16th °Aggregate - 12 digit

HUCs

USGS Regression-based model

Regressions applied based on region

Historical and future P from climate models

USGS VIC

Comparing Results

Shows increases in annual precipitation only

No response to warmer temperatures or the changing seasonality of precipitation

Captures the temporal and spatial variability in the climate models

Responds to future warming and increases in winter precipitation with a rise in flood severity

Difference of Sensitivity

Shift in Flood Severity

1/16th degree 12-digit HUCs

Comparing the Future to Historical 100-Year Flood – 2040s

Map: Rob Norheim

Shift in Low Flow SeverityComparing the Future to Historical 7Q10 – 2040s

1/16th degree 12-digit HUCs

Map: Rob Norheim

Summary Statistics: Low Flow

Summary Statistics: Flood

Future Applications

Implement extreme streamflow analysis over PNW domain

Assess changes in risk to fish habitat and infrastructure in other National Forests/Parks:

North Cascades

Mt Baker/Snoqualmie

Mt Rainier