THE IMPACT OF CLIMATE CHANGE ON WATER

SUPPLIES

Jim Doane PE

Spring 2004

Order of Presentation

• What is Current – Unprecedented issues for water supply planning– There will be temperature changes as a result of

human activity– How these changes impact the hydrology of the

Pacific Northwest– How these changes impact the Bull Run Water

System

Order of Presentation

• What is emerging– Worst case Pentagon Study on Climate Change

(Leaked to British Press in Feb 2004)• Collapse of the Atlantic Ocean’s thermohaline

circulation– Caused by Global Warming

– Change in years instead of decades as presently predicted

– Vast climate changes---both globally and locally

– Colder, windier and drier and shorter growing season in the Northeast US. Less productive agriculture.

Order of Presentation

– A longer growing season in the Southwest US. More productive agriculture if water can be provided.

– Increased competition for water leading to international conflict.

– http://www.ems.org/climate/pentagon_climatechange.pdf

Planning for Water Supply

• Based on historical values– Demand….present demand plus growth

(generally population based)– Supply

• Historical Record

• The longer the record, the higher the confidence

• But the Past is no longer a good precursor of the future

TEMPERATURE CHANGES

• From 2001 Work by the University of Washington

• Dr. Philip Mote of the JISAO Climates Impacts Group

Assessments of Climate Change

• Thousands of peer-reviewed papers

• Peer-reviewed assessment: Intergovernmental Panel on Climate Change (IPCC)

• Major reports in 1990, 1996, 2001

• National Academy of Sciences panel, 2001 underscored IPCC conclusions

• carbon dioxide concentration has increased by ~32%

• the carbon budget: nature has absorbed roughly half our emissions

• there is no question that the increase is unnatural

• from a very long term perspective, these changes are enormous

Humans will keep increasing CO2

Evidence that Earth is Warming

• Thermometers show warming of 0.4-0.8°C (0.7-1.4°F) since 1900

• Arctic permafrost is melting• Worldwide, most glaciers melting• Arctic ice thinning• Spring coming earlier (snow cover; blooming, leafing-

out dates)• Borehole temperatures indicate warming• But: not every station shows warming; upper-air

temperatures not increasing (satellites, balloons)

Global average temperature

1860 1880 1900 1920 1940 1960 1980 2000

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Some Evidence that Humans are Responsible

• Rate of warming unusual

• Hard to explain as natural (volcanoes, solar, ocean)

• Pattern of warming (and stratospheric cooling) consistent with human influence

The earth is warming -- abruptly

Natural Climate Influence Human Climate Influence

All Climate Influences

Projections into the Future

• Projections of future greenhouse gases (depends on socioeconomic projections)

• Climate models: different “sensitivity”

• Wide range of estimates: 1.4-5.8°C (2.5-10.4°F) by 2100, faster than any time in at least 10,000 years.

• Estimates show Pacific Northwest will increase by 3-5°F by 2040.

Temperature trends in the PNW

• Almost every station shows warming (filled circles)

• Urbanization not a major source of warming

PNW average temperature

Northwest warming

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Temperature Change Conclusions

• The bulk of the evidence points to a human influence on climate, with a global warming of 2.5-10.4F likely in the next 100 years.

• Regional warming likely to be faster than average global warming (3-6°F by 2040s); main vulnerability: reduced snow leading to summer water shortages

Implications for Water Management

• 2001 Work by University of Washington

• Alan Hamlet, Andy Wood and Dennis Lettenmaier of the JISAO Climates Impacts Group

WinterPrecipitation

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Hydrologic Characteristics of PNW Rivers

Temperature warms,precipitation unaltered:

•Streamflow timing is altered• Annual volume stays about the same

Precipitation increases,temperature unaltered:

•Streamflow timing stays about the same•Annual volume is altered

Sensitivity of Snowmelt and Transient Riversto Changes in Temperature and Precipitation

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Cedar RiverWestern Cascades

(caused predominantly by warm temperatures)

Columbia Riverat The Dalles

(caused both by warm temperatures and decreased precipitation)

Effect of 1992 Winter Climate on Two PNW Rivers

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Model

VICHydrology Model

Changes in Mean Temperature and

Precipitation from GCMs

Climate Change Scenarios 2020s

Climate Change Scenarios 2040s

The main impact: less snow

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Water Resources in the Columbia River Basin

System objectives affected by winter flowsWinter hydropower production (PNW demand)

System objectives affected by summer flowsFlood controlSummer hydropower production (California demand)IrrigationInstream flow for fishRecreation

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Simulated Reliability of Water Resources Objectivesfor “Middle-of-the-Road” Scenarios

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Yakima River at Kiona

General Conclusions for the PNW PNW hydrology is predominantly controlled by winter conditions in the mountains. Warmer temperatures produce streamflow timing changes in most PNW basins. Changes in precipitation produce changes in streamflow volumes. Basins encompassing the mid-winter snow line are most sensitive to warming. Basins at high elevations with cold winter temperatures are less sensitive.

The primary impact of warming in the PNW is loss of mountain snowpack. For the scenarios investigated, both warm/wet and warm/dry scenarios result in decreased snow water equivalent in the Columbia basin.

Warmer temperatures generally results in higher winter flows, lower summer flows, and earlier peak flows

Effects to the Columbia water resources system are largely associated with reduced reliability of system objectives affected by summer streamflows (water supply, irrigation, summer hydropower, instream flow).

There are significant uncertainties regarding changes in precipitation and the resulting intensity of reductions in summer streamflows and increases in the frequency of droughts.

However, a consistent and robust result is that some reduction in summer streamflow and increase in drought frequency is present in all scenarios by the 2040s for the Columbia basin.

The greatest impacts to the Columbia system are for the warm/dry scenarios, which produce the strongest reductions in summer streamflows and the greatest increases in drought frequency.

The reductions in summer streamflows in these scenarios are likely to exacerbate existing conflicts over water, the impacts of regional growth, and weaknesses in infrastructure, water management practice, and management institutions.

General Conclusions for the PNW (cont.)

The Impacts of Climate Change on Portland’s Water Supply

Work by Joe Dvorak, Dennis Kessler, Azad MohammadiPortland Bureau of Water Works

Richard Palmer, Margaret HahnUW Dept of Civil EngineeringClimate Impacts Group, JISAO

Spring 2002

Objectives Of Study

Examine the impacts of climate change on the Bull Run Watershed:

• Bull Run Watershed hydrology

• temporal and spatial analysis

• Forecasted M&I demand

• System performance

Portland’s Water Supply System

• Serves ~ 840,000 people• Largest system in state; serving since 1895• 42 BG annual demand• 115 MGD average daily demand• Bull Run Watershed

– Dam No.1 (10 BG)

– Dam No.2 (7 BG)

Bull Run Watershed

• 107 square miles

• 2350 feet elev.

• Rainfall driven

• 80 in./yr. rainfall

• 170 BG/year yield

• Peak Snowpack:– 16 inches Snow Water Equivalent (SWE)

• Snowmelt typically occurs before June

Methodology

Three sets of models used in the study:

Four Global Circulation Models

Hydrological Model

WaterSupply Model

Predicts changes to temperature and precipitation based on altered CO2 concentration.

Uses GCMs to predict climate impacted runoff in watershed.

Forecasts system performance based predicted watershed hydrology.

Results: Impacts to Climate

• Average warming trends of ~1.5 OC for the 2020

decade and ~2 OC by 2040.

• Increased winter precipitation, with less snowfall,

but more rain

• A decrease in late spring and summer precipitation

Results: Impacts to TemperatureTemperature Change

for Climate Change Scenarios

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Results: Impacts to Snowfall

Results: Impacts to PrecipitationPrecipitation Fraction for

Climate Change Scenarios

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Results: Impacts to Hydrology

• Average winter streamflows increase by 15%

• Late spring streamflows decrease by 30% due to spring

snowmelt being non-existent

• 50 percent of the time, April to September flows may decrease

by as much as 12.9 BG

• Less impact to storage (0.1 - 3.6 BG) depending on drawdown

timing (avg. 1.3 BG)

Results: Impacts to Streamflow

Results: Impacts to Streamflow(April to September)

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Current Climate

Results: Impacts to Demand

• Water demands shown to be less sensitive to

climate change than hydrology

• 8% increase in 2040 drawdown demand

• 4% increase in 2040 average annual demand

Results: Impacts to Demand2040 Forecasted M & I Demand (includes conservation)

30-day Moving Average

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No Global Warming

Results: Impacts to Drawdown

Impacts to drawdown length will vary

from year to year:

Historical extreme years like 1987 change little, however, the

frequency of these years increases.

Drawdown length for average years may increase by as much as

60 days, as drawdown starts earlier due to early spring recession.

Results: Impacts to System

• On average, the combined effect of climate

change on hydrology and demand may increase

storage requirements by 2.8 BG.

• Global warming will push forward the need to

provide more sources of supply in the future

Impacts to Bull Run Watershed

Impacts to Overall System

Summary

• Warming trends of 1.5 OC (up to 3.5 OC) for 2020 and 2.0 OC (up to 4.5 OC) by 2040.

• Average winter precipitation will increase, late spring runoff will decrease, spring

snowmelt may be non-existent.

• Streamflows in the summer will decrease.

• The impacts on hydrology may increase storage requirements by 1.3 BG (up to 3.6

BG)

• Demands will increase by 1.5 BG (up to 2.4 BG)

• The effect of climate change on hydrology and demand, will increase storage

requirements by 2.8 BG (up to 5.4 BG)

Conclusions• Assessing climate change impacts will be vital in future water

supply planning.

• Climate change is only one factor in long-term planning. Other

factors will include:

– Future demands (due to growth and/or service area changes)

– ESA (fish flow releases)

– Conservation Programs, investments & success

The Future

• JWC has a similar study underway now– JWC supplies Hillsboro, Beaverton, Forest

Grove and TVWD

• Results are expected this summer

• Expect results to be similar to Bull Run

• Vector Issues

Impact of the Emerging Data

• We have only the summary of the leaked Pentagon Study – We don’t yet have the necessary specifics

• To evaluate its validity or likelihood

• To anticipate what impact the loss of the Atlantic termohaline circulation will have on the Pacific Northwest

• To see how much this throws off the information I have presented today.

The Engineering Community

• Meeting with other engineering working on climate change issues.– Providing information– Trying to educate other engineers– Trying to educate the public at large– Trying to educate elected officials

Acknowledgements

• The slides showing the impacts of temperature change are by Dr. Philip Mote of the JISAO Climates Impacts Group.

• The slides showing the impacts on water resources are by Alan Hamlet, Andy Wood and Dennis Lettenmaier of the JISAO Climates Impacts Group.

Acknowledgement Cont.

• The slides on the Portland Study are by Richard Palmer, Margaret Hahnof the JISAO Climates Impacts Group.

• Assisting my understanding of the issues of Portland’s water supply were Joe Dvorak, Dennis Kessler, Dr. Azad Mohammadi of the Portland Water Bureau