Alan F. HamletEric P. SalathéMatt StumbaughSe-Yeun LeeSeshu Vaddey

• U.S. Army Corps of Engineers• JISAO Climate Impacts Group• Dept. of Civil and Environmental Engineering• University of Washington

Estimates of 21st century flood risk in the Pacific Northwest based on regional scale climate model simulations

Motivation

Role of Atmospheric Rivers in Flooding (Nov 7, 2006)

Neiman, PJ, LJ Schick, FM Ralph, M Hughes, GA Wick, 2011: Flooding in Western Washington: The Connection to Atmospheric Rivers, J. of Hydrometeorology, (accepted)

Effects of Projected Warming and Precipitation Change on 21st Century Flood Risk from Previous Research

Mote, P.W. and E. P. Salathe Jr., 2010: Future climate in the Pacific Northwest, Climatic Change, DOI: 10.1007/s10584-010-9848-z

21st Century Climate Impacts for the Pacific Northwest Region

Seasonal Precipitation Changes for the Pacific Northwest

Mote, P.W. and E. P. Salathe Jr., 2010: Future climate in the Pacific Northwest, Climatic Change, DOI: 10.1007/s10584-010-9848-z

Relationship Between Change in Q100 and Winter Temp

http://www.hydro.washington.edu/2860/products/sites/r7climate/study_report/CBCCSP_chap7_extremes_final.pdf

Improving Flood Risk Projections Using High Resolution Regional

Climate Models

Regional Climate Modeling at CIG WRF Model (NOAH LSM) 36 to 12 km

ECHAM5 forcing CCSM3 forcing (A1B and A2 scenarios)

HadRM 25 km HadCM3 forcing

Snohomish River Near Monroe, WA

Simulated Changes in Storm Characteristics

Simulated Storm Event on 2030-11-27 ECHAM5 A1B

Simulated Storm Event on 2056-11-20 ECHAM5 A1B

Preliminary Results for the ECHAM5 A1B Sceario for the 2050s.

Chehalis River at PorterD

aily

Pea

k F

low

(cf

s)

Dai

ly P

eak

Flo

w (

cfs)

Date of Peak Flow (1 = Oct 1) Probability of Exceedence

ECHAM5 2050 A1B ECHAM5 2050 A1B

Sauk River near Sauk

ECHAM5 2050 A1B ECHAM5 2050 A1B

Dai

ly P

eak

Flo

w (

cfs)

Dai

ly P

eak

Flo

w (

cfs)

Date of Peak Flow (1 = Oct 1) Probability of Exceedence

Relationship Between Change in Q100 and Winter Temp

0

1

2

3

-15 -10 -5 0 5 10

Flo

od R

atio

DJF mean temp (C)

0

1

2

3

-15 -10 -5 0 5 10

Flo

od R

atio

DJF mean temp (C)

RCM based on WRF echam5 A1B:

100 year flood ratio of the 2050s to the 1980s

GCM based on Hybrid delta echam5 A1B:

100 year flood ratio of the 2040s to historic runs

Conclusions:

• Our initial exploration of changing flood risk in the PNW using statistical downscaling points to increasing flood risk in most areas of the region due to projected regional warming and increases in cool season precipitation.

• Regional climate models offer more physically based assessment tools for understanding the potential changes in nature of extreme storms (such as atmospheric rivers), the timing of flooding, and a potentially improved picture of the spatial variations in changing hydrologic extremes across the region.

• Initial results suggest more extreme storms in the early fall and general increases in flood intensity will accompany global climate change in the PNW. In particular, many sites show shifts towards flooding earlier in the water year due to the combination of changes in snowpack and earlier storms.