ClimateChange,HeavyRains,and

FloodinginKingCounty

ResearchTeamGuillaume Mauger, UW Climate Impacts GroupSe-Yeun Lee, UW Climate Impacts GroupJason Won, UW Climate Impacts GroupKatherine Hegewisch, U. Idaho Department of GeographyCary Lynch, Connecticut Department of Energy & EnvironmentRaquel Lorente Plazas, Univ. of Murcia, SpainYolande Serra, UW JISAOEric P. Salathé Jr., UW Bothell

ResearchTeamDepartmentofNaturalResourcesandParksDirector’sOffice

LaraWhitelyBinder

WaterandLandResourcesDivisionRiverandFloodplainManagementSectionKyleComanorFredLottBrianMurrayLorin ReineltJeanneStypula

WaterandLandResourcesDivisionScienceandTechnicalSupportSection

CurtisDeGasperi (ProjectManager)JimSimmonds

Historical

Low Emissions (RCP 4.5)

High Emissions (RCP 8.5)

1950 1975 2000 2025 2050 2075 2100

0°F

5°F

10°F

15°F

0°F

5°F

10°F

15°F

Year

Temperature Difference(Relative to 1950−1999 average)

Year

Precipitation Change(Relative to 1950−1999 average)

1950 1975 2000 2025 2050 2075 2100

−40%

−20%

0%

20%

40%

60%

−40%

−20%

0%

20%

40%

60%

Substantial Warming, Variable Rainfall

Wheredotheseprojectionscomefrom?

https://serc.carleton.edu/eet/index.html

Warner, Mass, Salathé, J Hydromet, 2014

Global models project an increase in heavy rains

Heaviest rain events are projected to become +22% more intense* (range: +5 to +34%) by the 2080s.

* Top 1% of daily rainfall totals in western WA & OR

Morerain,NOTbiggerstorms

FIG. 2. CMIP5 RCP 8.5 10-model means (boldface lines) for (a),(b) 99th percentile IVT(upper values, solid) and winter mean (lower values, dashed) for (left) 1970–99 (boldface blue)and (right) 2070–99 (boldface red) along the 13-grid-box transect in Fig. 1. Only October–March is considered. Light blue and red lines are individualmodels, and boldface green lines onthe left are NCEP–NCAR reanalysis values for 1970–99. Right-hand plots also show themultimodel means of the historic period for reference (boldface blue lines, same on left andright). Similar plots for (c),(d) IWV; (e),(f) 850-hPa total wind; and (g),(h) daily precipitationare also shown.

122 JOURNAL OF HYDROMETEOROLOGY VOLUME 16

2080s

1980s

MoreWaterVapor

Morerain,NOTbiggerstorms

FIG. 2. CMIP5 RCP 8.5 10-model means (boldface lines) for (a),(b) 99th percentile IVT(upper values, solid) and winter mean (lower values, dashed) for (left) 1970–99 (boldface blue)and (right) 2070–99 (boldface red) along the 13-grid-box transect in Fig. 1. Only October–March is considered. Light blue and red lines are individualmodels, and boldface green lines onthe left are NCEP–NCAR reanalysis values for 1970–99. Right-hand plots also show themultimodel means of the historic period for reference (boldface blue lines, same on left andright). Similar plots for (c),(d) IWV; (e),(f) 850-hPa total wind; and (g),(h) daily precipitationare also shown.

122 JOURNAL OF HYDROMETEOROLOGY VOLUME 16

2080s1980s

NochangeinWinds

Whatdoesthismeanforus?

Source: Kitsap Sun

“Downscaling”relatesthelargetothesmall

~100-200km(~60-120mi)resolution

~6km(~4mi)resolution

ResultsfromStatisticalDownscaling

WarmBasinsColdBasins

Salathéetal2014

Itmattershowyoudoit.

2040s,A1B

WarmBasinsColdBasins

Salathéetal2014

ResultsfromDynamicalDownscaling

Itmattershowyoudoit.

2040s,A1B

RegionalClimateModelProjections

https://twitter.com/LigaDos32

Findings:ChangeinHeavyRains

Howwelldoweknowourcurrentrisk?

“100-yearevent”

Heavy Rains at Sea-Tac

Low-End Projection High-End Projection

24-hour Rainfall

Changeinthe100-yrstorm

Whatdoesthismeanforflooding?

kingcounty.gov

Green,Snoqualmie,andSouthForkSkykomish rivers

Ashiftfromsnowtorainforbothrivers

Snoqualmie GreenWinter(Dec-Feb)

+10% +16%

Summer(Jun-Aug)

-70% -60%

(tableliststheminimumchangeamongthetwoprojections,relativetotheaveragefor1970-1999)

Changeinaveragestreamflowforeachseason,2080s:

SnoqualmieRiverfloods,2080s:

(USGSsite:SnoqualmieRNearSnoqualmie)

Isfloodingactuallydecreasing?

GreenRiverfloods:

ChangeinPeakFlow

s(%)

(3-hourflows) (dailyflows)

NoDam Dam

Outlook:What’snext?

• MoreRegionalModelProjections

• SamemodelingforWhite/Cedar

• Futurefloodmapping

seattletimes.com

fema.gov

GuillaumeMaugerUWClimateImpactsGroupcig.uw.edugmauger@uw.edu(206)685-0317

VictoriaPinheiro,UW

https://cig.uw.edu/our-work/applied-research/heavy-precip-and-stormwater/https://cig.uw.edu/our-work/applied-research/effect-of-climate-change-on-flooding-in-king-county-rivers/

Isfloodingactuallydecreasing?