Climate Change and Flooding in Wisconsin

Ken PotterDepartment of Civil & Environmental Engineering

University of WisconsinMadison, WI

2011 WAFSCM Annual ConferenceNovember 3, 2011 - Pewaukee

Outline

• Global Circulation (Climate) Models (GCMs)

• WICCI findings based on statistical downscaling of GCMs

• New findings based on Regional Circulation (Climate) Models (RCMs)

• NOAA Atlas 14

• Storm transposition for vulnerability assessment

General Circulation Models

IPCC 2007

General Circulation Models (GCMs)simulate the effects of incoming and outgoing thermal radiation on global circulation, and include:

Atmosphere

Clouds

Oceans

Topography

Rainfall

etc.

Dynamical Downscaling(Regional Circulation Models, RCMs)

Statistical Downscalingof GCM output

6 RCMs drivenby 4 GCMs

North Americandomain

Modern: 1970-2000Future: 2038-2070

3-hourly output,Many variables

(T, P, H, SM, etc.)50 km horizontal

resolution

20 GCMsWisconsin

domainModern: 1950-2000Future: 2001-2100

Daily output,Fewer variables

(T, P, H?)

10 km horizontalresolution

Climate Model Projections

Downscaling: Focus global projections to a scale relevant to climate impacts in Wisconsin

Wisconsin Initiative for Climate Change Impacts• Used 14 General Circulation Models (GCM’s) from IPCC 2007 assessment

• Debiased and downscaled using historical Wisconsin weather station data

• Result: a statistical range of potential climate change

GCM grid Downscaled (8x8 km) grid

D. Vimont, UW-Madison

Temperature (°F)

Significant warming is projected

Change in average annual temp 1980 to 2055

PrecipitationChange in annual average

1980 to 2055 (inches)

1.25” to 2.25” and 2-3 days/decade = modest future increase

Increase in 2” rainfalls 1980 to 2055 (days/decade)

Winter Precipitation1980 to 2055

Precipitation as snow reduced by 20% by mid-century

= 30% decrease in midwinter snow depth

Notaro et al. 2010

Reduced Snowfall (%)Increasing (water inches)

Increased Winter Rainfall

Potter and Liebl, 2010

More rain in winter

+More intense rainfall

= More high water events?

= More groundwater recharge?

Gordy Stephenson

Cottle

Vulnerability is already high during winter and spring

DNR

Increased Winter-Spring Flooding?

Based on statistically downscaled data developed by Kucharik, Lorenz, Notaro, and Vimont, UW Madison.

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2-Year Recurrence Interval

100-Year Recurrence Interval

Quantile Projections: Madison

Large Uncertainty in Rainfall Projections

Which 100-year event do you prefer ?

6”or 9”

Projected size of 100-year 24-hour storm for Madison, WI, based on 14 GCMs

Schuster, et al

? Wetter or drier in summer ?

What about Regional Circulation Models (RCMs)?

• Recently developed by North American Regional Climate Change Assessment Program (NARCCAP)

• 6 RCMs driven by 4 GCMs

• North American domain

• 1970-99; 2040-69

• 3-hourly output

• 50 km resolution

RCM 100-Year, 24-Hour Rainfalls for Madison

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RCM 100-Year, 24-Hour Rainfalls for Green Bay

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RCM 100-Year, 24-Hour Rainfalls for Milwaukee

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Quantile-Quantile Plots for Top 100 Daily RCM Rainfalls: Madison

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What do others think about precipitation modeling?

Science Magazine, October 2011:

When the Seattle Public Utility asked University of Washington climate scientist

Clifford Mass how big they should build the pipes in a $750M storm drainage system, he

“couldn’t give them an answer.”

And a University of Wisconsin professor…

In the same Science article, University of Wisconsin Professor Greg Tripoli points out that global circulation models can’t

“create the medium-size weather systems that they should be sending into any embedded regional model.”

So what should we do about engineering design?

The record we use may actually reflect a drier period (TP40, 1938-1958).

Are we designing for historical climate?

Hydrologic design is based on experience. (i.e. history)

NOAA Atlas 14Updating TP-40

Provides data for locations

vs. TP-40 isohyetal maps

South Beloit. IL

More stations

TP-40 vs. NOAA Atlas 14

Record n Years (avg)

Hourly Stations 200 vs. 994 14 vs. 40

Daily Stations 1350 vs. 2846 16 vs. 63

Longer period of record

Revised statistical method

Davis Todd, et al 2006

NOAA Atlas 14 – Updated Design Storms

Davis Todd, C.E., J.M Harbor, B. Tyner, Increasing Magnitudes and Frequencies of Extreme Precipitation Events Used for Hydraulic Analysis in the Midwest,

Journal of Soil and Water Conservation, (61)4:179-184, 2006

NOAA Atlas 14 - a work in progressMidwest States - due late 2012

http://www.nws.noaa.gov/oh/hdsc/current_projects.html

Storm transposition can be used to asses vulnerability?

The 2008 storm in the Midwest could be used this way.

What else can we do, given GCM uncertainties?

“Build upon the experiences of communities that have experienced recent extreme rainfalls to guide a state-wide evaluation of vulnerabilities...” - WICCI Stormwater Working Group

Vulnerability assessment

Assess: • Floodplains and surface flooding• At-risk road-crossings• Stormwater BMPs• Sanitary sewer inflow and infiltration• Emergency response capacity• Wells and septic systems• Hazardous materials storage

Building Long Term Resilience

• Planning for impacts 25 or 50 years out is challenging

• Adaptation to low-risk high-cost events requires political support

• Can use simulations to understand high water impacts

Conclusions

• Rain event intensities will likely increase in WI due to climate change, but the modeling results do not provide a sufficient basis for engineering design.

• Winter-spring precipitation changes appear to be better supported. Runoff implications need further study.

Conclusions

• NOAA Atlas 14 should be adopted statewide when available.

• Storm transposition should be explored as a method of evaluating vulnerabilities and increasing resilience.

Questions?