The Impacts of Climate Change on Portland’s Water Supply

Richard Palmer and Margaret HahnUniversity of Washington

Department of Civil and Environmental Engineeringand Climate Impacts Group, JISAO

Joe Dvorak, Dennis Kessler, Azad Mohammadi Portland Bureau of Water Works

Objective of Study

• Explore the impacts of climate change on

– Bull Run Watershed

– Hydrology

– Water reliability

– Policy

Talk Overview

• Introduction

• Watershed Hydrology

• Models

• Impacts on Watershed

• Impacts on Demands

• Impacts on System Performance

• Conclusions

Bull Run Watershed

Bull Run Watershed Stats• Area: 107 square miles

• Average elevation : 2350 feet

• Average productivity : 8 cfs/square mile

• Average Rainfall : 43 inches

• Average April snowpack : 16 inches SWE

Portland System

• Serves ~ 780,000 people

• Surface Water

– Bull Run Watershed

(215 MGD capacity)

• Groundwater

– Columbia South Shore Wellfield

(90 MGD capacity)

Evaluation of Climate Change

• Meteorological data

• Climate Shift

• Hydrology model

• Calibration

• Impacts Evaluation

Precip and temp

Downscaled GCM

DHSVM

Historic vs Simulated

System Simulation model

Hydrology Highlights

• Bull Run is a rainfall driven watershed

0.0

0.5

1.0

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10 11 12 1 2 3 4 5 6 7 8 9

Month

No

rmal

ized

Str

eam

flow

SnowDominated

Transient Snow

Rain Dominated

Hydrologic Characteristics of PNW Rivers

Average Monthly Values for Flow and Precipitation

Bull Run Watershed

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Bull Run Flows near Multnomah Falls

Bull Run Precipitation at Headworks

Annual Average Bull Run Inflows1950-1999

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Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

Inflo

ws,

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Precipitation falling as both rain and snow

Precipitation falling as rain

Hydrology Highlights

• Snow melt typically occurs before July

Average Monthly Snow Water Equivalent (1979-1999) North Fork Bull Run Snotel Site # 22D02S

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ater

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Models Used to Evaluate Climate Change

• General Circulation Models

• Distributed Hydrology, Soil-Vegetation Model

• Supply and Transmission Model

GCM Models Used• HadCM2 and HadCM3

– Hadley Centre of United Kingdom– Used in IPCC report

• ECHAM 4 – Max Planck Institute of Germany– Used in IPCC report

• PCM3– US Department of Defense, US Army Corps of

Engineers, Los Alamos National Laboratory

• Characterizes basin hydrology with – Elevation, aspect and slope data– Soil type and vegetation data– Stream network– Meteorological data – Energy balance for snow– Mass balance for precipitation and run-off

DHSVMDistributed Hydrology, Soil-Vegetation Model

DHSVMDistributed Hydrology, Soil-Vegetation Model

Observed and 2040 Climate Change Average Monthly Temperature

at Headworks for Bull Run

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25

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

Mo

nth

ly T

emp

erat

ure

, d

egre

es C

observed (1961-1990)

PCM3 2040

ECHAM4 2040

hadCM2 2040

hadCM3 2040

Temperatures will increase by 2° C by 2040, with higher temperatures in the summer

Precipitation will increase in the winter and decrease in the summer.

Observed and 2040 Climate Change Average Monthly Precipitation

at Headworks for Bull Run

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nth

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reci

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observed (1961-1990)PCM3 2040ECHAM4 2040hadCM2 2040hadCM3 2040

Average Monthly Bull Run Inflows1950-1999

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Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

Inflo

ws,

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Current ClimatePCM3 2040ECHAM4 2040HadCM2 2040HadCM3 2040

Impacts of Climate Change on Watershed

Seasonal Cumulative Flows (April-September)Combined Bull Run River Inflows

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Exceedance Probability

cfs-

days

Current ClimatePCM3 2040ECHAM4 2040HadCM2 2040HadCM3 2040

Bull Run River Flows into Dam 1Current Climate and 2040 Climate Change

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Oct-65 Dec-65 Feb-66 Apr-66 Jun-66 Aug-66 Oct-66

cfs

Current ClimatePCM3 2040ECHAM 2040HadCM2 2040HadCM3 2040

Climate Change Impacts on 1966 Hydrology

ECHAM4 Decade 2040 Climate Change Impacts Measured as Difference in Annual Minimum Storage less Shortfalls

from Current Climate/Current Demands (2000 Demands)

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Climate impact onhydrology

Climate impact ondemand

Impact of growth ondemand 2040

Impact of climatechange on 2040

demand andhydrology

Mil

lio

n G

alll

on

s

1952196619681982198719921994

ECHAM4 Decade 2040 Climate Change Impacts measured as Reduced Storage Value from

Current Climate/ 2000 Demands

Impacts on StorageExceedance Probability of Minimum Storage less Shortfalls

for the Combined Bull Run Storage for 2000 Demands and 2040 Climate Change Scenarios

6,000

7,000

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0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0Exceedance Probability

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imu

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tora

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ort

fall

s,

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lio

n G

all

on

s

2000 - Current Climate2000 - PCM3 20402000 - ECHAM4 20402000 - HadCM2 20402000 - HadCM3 2040

Impacts of growth and climate change on reduced storage

Exceedance Probability of theDifference in Annual Minimum Storage less Shortfalls

from Current Climate and 2000 Demands

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Exceedance Probability

Mill

ion

Gal

lon

s

Current Climate / 2040 Demands

ECHAM4 2040 / 2000 Demands

ECHAM4 2040 / 2040 Demands

climate change

and growth

growth

climate change

Exceedance Probability of Reduced Storage Value from Current Climate and

2000 Demands

Simple Translation

• Forecasted Regional Growth will result in 40 mgd additional demand

• Climate change impacts will increase this by another 20 mgd

Conclusions• Rainfall controlled system

• Temperature signal of 2 C

• Climate impacts are not uniform

• Shift in quantity and timing of snowpack

• Impacts of climate reduces storage 2.8 BG

• Average loss of 20 mgd due to climate change

• Climate change is only one factor that will contribute to the need for more “supply”