Precipitation Patterns, Supply Planning and Demand Curves:

Assessing Water Supply Risks in a Changing Climate

Erica BrownAssociation of Metropolitan Water Agencies

(AMWA)May 21, 2015

NOAA CPO Third Thursday Webinar SeriesClimate Information for Managing Risks in Water Resources

Overview

Water supply planning: what the demand curves show buys utilities time, re: for supply development

Two illustrative examples from: Seattle/Cascade Water Alliance and extreme events Tarrant Regional Water District and prolonged

drought

Near-term (and long term) informational and forecast needs and improvements

Regional-long term resilience planning

Case examples for today’s talk

Seattle Public Utilities/Cascade

Water Puget Sound region, Pacific NW

Seattle supplies finished water to Cascade Water and its population

Pop. Served 1.45 M Short on storage, long on

precip.

Tarrant Regional Water District

North Central Texas Supplier of raw water to

30 wholesale customers in 11 counties

Pop. served 1.7 M Long on storage, short on

precip.

These two agencies, like most around the U.S., have declining demand despite population growth.

Nationally, water use in the U.S. for public supply declined by 5% between 2005 and 2010 (USGS, 2014)

Water Consumption Is Declining

Shifting Water Demand Forecasts(Seattle Public Utilities, Including

Cascade)

5

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0

100,000

200,000

300,000

400,000

500,000

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1,300,000

1935

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To

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Growth in Population and Water ConsumptionSeattle Regional Water System: 1935- 2013

Population

Consumption in MGD

P

Factors causing changes in demand trends

Plumbing efficiency and regulation

Housing stock and density

Conservation behavior and technology

Water system efficiency

Kind of water use Irrigation Residential Business

Population demographics

Water use policy and pricing

Lower demand buys time for supply development

Short on storage – long on water

• Snow=savings plan• Rain=checking account• Near term: managing

operationally with the best data and information they have.

What does snowpack will decline mean?

Seattle Area climate issue: amount and timing of precipitation/runoff

As long as you’re not in the red, you don’t need a savings account. Keep making deposits into checking and you’re good. – Chuck Clarke, Cascade Water Alliance CEO

Source: SPU

Management of reservoirs based on detailed watershed

simulation model

Source: SPU

TRWD climate issue: drought

Long on storage, short on water.Drought Risks: • Transmission

capacity• Reliability• Source supply

availability

The 20-mile Eagle Mountain Connection allows TRWD to extend the reach of water from its E. TX reservoirs to Eagle Mountain Lake via storage and transmission facilities.

Source: Freese.com

Palmer Index History - extreme drought

FSource: TRWD

TRWD Demands Over Time

Forecasts and information helpful for extreme event planning

Continued refinement and improvements are always welcome! Improvements in 1-3 day forecasts (reliability,

specificity) - Seattle Improvements in confidence levels for 7-14 day

forecasts - Seattle and Tarrant Improvements in seasonal outlooks for

precipitation - Seattle Improved bounding of uncertainties in

forecasts that do exist (e.g., Dec. 2014 Pineapple Express event; ensembles of QPF forecasts) –- Seattle and Tarrant

Water Resilience in the Future

Water Resilience in the Future

TarrantRegional water

planning (legislated)5 year plan – but

looking at 50 years out for population and demand

Seattle/CascadeRegional water

planning (voluntary) Long term outlooks

(20-year) continually updated with new (population and climate) scenarios, inputs

Thank you

Erica Brown

AMWAbrown@amwa.net202-331-2820

Thanks to: Laura Blaylock, Tarrant

Regional Water District Julie Hunt, Trinity River

Authority of Texas Chuck Clarke, Cascade

Water Alliance Alan Chinn, Paul

Fleming, Seattle Public Utilities

Extra slides

Cascade Water Alliance Service Area

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An

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Total Seattle Regional Water System Annual Demandin Millions of Gallons per Day: 1930-2013

121 mgd

171 mgd

Seattle Public Utilities

Cascade Average Daily Demand(million gallons per day)

30

35

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45

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55

2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

2004 TSP Composite Projection

2004 Financial Forecast

Actual Total Demand

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City of Phoenix Water Services Department Water Production & Wastewater Generation

Wastewater Generation Water ProductionPopulation

Million

Gallon

s p

er

Day

Pop

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tion

19861987

19881989

19901991

19921993

19941995

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19981999

20002001

20022003

20042005

20062007

20082009

20102011

20122013

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Estimated Average Outdoor July Water Use (GPD: July Use Less February Use)

for All Phoenix Single Family Residences 1986-2013

Gallo

ns P

er D

ay

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Average Daily Water Use (2010-2013, Gallons Per Day) for Phoenix Single Family Residences by Year of Home Construction

4-Yr Avg Daily Water Use (Gallons)

Year of Construction

Gal

lons

Per

Day

Example: Seattle

Source: SPU

Seattle: precipitation on track

Source: SPU

Seattle: reservoir storage on track

Source: SPU