Climate Change: Impact on water in the western United

States

Tim P. BarnettDavid W. Pierce

Scripps Institution of OceanographyLa Jolla, CA

Effect of Climate Change on Western U.S.• Large and growing population in a semi-

arid region• How will it impact water resources?• Use an “end-to-end” approach

Project overview

Projected change in California snowfall...

Projected change by 2050

Downscaling: the motivationGlobal model (orange dots)

vs. Regional model grid (green dots)

How good is the Hydrological Model?

Andrew Wood, Univ. of Washington

River flow earlier in the year

Runoff already coming earlier

Columbia Basin Options

Hydropower

Or

Salmon

California: Mandated water releases cannot be met

Colorado River: Not enough water to meet current demands

10 million people in Los Angeles

Los Angeles water shortage

Christensen et al., Climatic Change, to appear

Miss water treaty obligations to Mexico

Christensen et al., Climatic Change, to appear

• Ratio of chlorophyll concentration in spring, 2090s/2000s.

Step 1• Begin with current state of global oceans

Why initialize the oceans?• That’s where the heat has gone

Data from Levitus et al, Science, 2001

How good is the ocean simulation?

Pierce et al, Climatic Change, to appear

Step 2• Estimate climate change due to emissions

Global Climate ChangeSimulation• Parallel Climate

Model (PCM)• Business as Usual

Scenario (BAU)• 1860-2100• Estimate Western U.S.

climate change

How well does the PCM work over the Western United States?

Dec-Jan-Feb total precipitation (cm)

Step 3• Downscaling and impacts

How good is downscaling?

El Nino rainfall simulation

Observations Downscaled model Standard reanalysis

Ruby Leung, PNNL

Results• Reduced snow cover• Earlier snow melt• Earlier spring flood crest• Shift in ‘Run off” season• Small rainfall reductions

Columbia River basin

Columbia River flow

Andrew Wood, Univ. of Washington

Sacramento/San Joaquin River basin

Sierra snow pack• Now and ………………….………….future?

Colorado River basin

Other impacts

• Increased wildfires• Salinification of Sacramento Delta• Extinction of Salmon in PNW?• Cities vs. Farming

More wildfires

100% more acres burned in 2100

Less time for Salmon to reproduce

Now:

Lance Vail,PNNL

Future:

Water use conflicts

Climate changes naturally

San Diego (CA) Union Tribune; Phil Caterion

Conclusions• Greenhouse induced climate changes will

have a massive impact on the water resources of the western United States.

• The fabric of life in this region will be greatly altered by these changes….a “train wreck” in the making.

• What you have seen is a “best case” scenario (it could be worse and/or happen sooner).