WATER RESOURCES and GLOBAL WARMING:

WHAT CAN WE EXPECT?

Dr. Christopher A. KentGeography, SCC

April 21, 2008

I. Background Comments on Global Warming

II. Changes in Global Hydrology

III. Changes in the Pacific Northwest

• Change occurs on many timescales simultaneously

• Not all places experience the same change (direction or rate)

• Data problems increase the further back in time one goes

Climate = pattern of weather in a region over long time periods- includes variability

Climate change can be natural

Climate change can be anthropogenicGlobal Warming = recent trend and projected

continuation of rising average temperatures . . . caused by human activities

I. BACKGROUND COMMENTS ON GLOBAL WARMING

Global Air Temperaturefrom 542,000,000 years ago

63F

72F

54F

Today: about 59F

Current Ice Age(last 1.8 million years)

Global Air Temperature, 1850-2005

Climate Research Unit (UK)

Norm = 1961-1990

Statistical noise = random variation about a mean

http://news.bbc.co.uk/2/hi/business/6098362.stm

Global Warming Artwork

Normal = 1940-1980

Increase, 1960 to 2060

10-10• bigger at high latitudes• bigger over continents• bigger in winter

»0.6C (1F) globally spatially uneven

1.5F in PNW over last 100 years

THE HYDROLOGIC CYCLE

NASA GSFC Water and Energy Cycle Program

Box TS.5, Figure 1. Schematic showing the effect on extreme temperatures when the mean temperature increases, for a normal temperature distribution.

IPCC = Intergovernmental Panel on Climate Change• established in 1988 by WMO & UNEP• several thousand scientists from around the world• assesses scientific information• shared 2007 Nobel Peace Prize

IPCC(DRY/WET) (WET/DRY)

Climate = pattern of weather in a region over long time periods- includes variability

HAZARDS ASSOCIATED WITH GLOBAL WARMING

1. Changes in climate patterns

2. Sea level rise

3. Increased Drought

4. Changes in the biosphere (including species extinctions)

5. Changes in global food production

6. Deforestation

7. Increased Wildfires

Examples:Changed El Nino cyclesChanged Precipitation

Changed Storm Intensity

Changes in Water Resources

Figure 10.12. Multi-model mean changes in (a) precipitation (mm day–1), (b) soil moisture content (%), (c) runoff (mm day–1) and (d) evaporation (mm day–1).

IPCC,2007

II. CHANGES IN GLOBAL HYDROLOGY

+7-15%by 2100

December – FebruaryPrecipitation2080 - 2099

IPCC,2007June - August

Precipitation2080 - 2099

(Temperature) (Atm. Pressure)

IPCC, 2002

ALTERED PRECIPITATION PATTERNS

IPCC, 2007

Figure SPM.7. Relative changes in precipitation (in percent) for the period 2090–2099, relative to 1980–1999. Values are multi-model averages based on the SRES A1B scenario for December to February (left) and June to August (right). White areas are where less than 66% of the models agree in the sign of the change and stippled areas are where more than 90% of the models agree in the sign of the change.

Increased Global Precipitation (2090-2099 relative to 1980-1999)

IPCC, 2007

December - February June - August

Figure 11.12. Temperature and precipitation changes over North America from the MMD-A1B simulations. Top row: Annual mean, DJF and JJA temperature change between 1980 to 1999 and 2080 to 2099, averaged over 21 models. Middle row: same as top, but for fractional change in precipitation.

North American Precipitation Changes (2090-2099 relative to 1980-1999)

Dramatic changes in runoff volume from ice-free land are projected in many parts of the world by the middle of the 21st century (relative to historical conditions from the 1900 to 1970 period). Color denotes percentage change (median value from 12 climate models). Where a country or smaller political unit is colored, 8 or more of 12 models agreed on the direction (increase versus decrease) of runoff change under the Intergovernmental Panel on Climate Change’s “SRES A1B” emissions scenario.

-40% 0 +40%

Changes in Runoff Volume: 2050 compared to 1900-1970Milly et al., 2008, Science Magazine

RUNOFFCHANGES

FAQ 5.1, Figure 1. Time series of global mean sea level (deviation from the 1980-1999 mean) in the past and as projected for the future. For the period before 1870, global measurements of sea level are not available. The grey shading shows the uncertainty in the estimated long-term rate of sea level change (Section 6.4.3). The red line is a reconstruction of global mean sea level from tide gauges (Section 5.5.2.1), and the red shading denotes the range of variations from a smooth curve. The green line shows global mean sea level observed from satellite altimetry. The blue shading represents the range of model projections for the SRES A1B scenario for the 21st century, relative to the 1980 to 1999 mean, and has been calculated independently from the observations. Beyond 2100, the projections are increasingly dependent on the emissions scenario (see Chapter 10 for a discussion of sea level rise projections for other scenarios considered in this report). Over many centuries or millennia, sea level could rise by several metres (Section 10.7.4).

RISING SEA LEVEL

220-500 mm = 9-20”

IPCC, 2007

1.2”/10 years

.07”/yr

Global warming & sea-level rise

Tuvalu

• rising sea level (3.5” to 34.6” by 2100)• increased & stronger storm activity• erosion (11.8” rise = 98’ shore retreat)• environmental refugees?

No orographic precipitation

(9-20”)

Figure 5. 20th century trends in average annual precipitation (1920-2000). Increases (decreases) are indicated with blue (red) dots. The size of the dot corresponds to the magnitude of change.

Figure 4. 20th century trends in average annual temperature (1920-2000). Increases (decreases) are indicated with red (blue) dots. The size of the dot corresponds to the magnitude of change.

Climate Working Group, University of Washington

III. CHANGES in the PACIFIC NORTHWEST

1920-2000Trends

Temperature Precipitation

1. Region wide warming of about 1.5F over 100 years

2. Increase in precipitation in most of the PNW

3. Decline in snowpack since 1950, esp. at lower elevations

4. Spring is arriving earlier (0-20 days since 1948)

PAST TRENDS

Climate Working Group, University of Washington

CWG, UW

More Rain, Less SnowReduced Snowpack

Relative Trend in April 1st Snow Water Equivalent (1950-2000)

AnnualPrecipitation

Changes in the Quantity and Timing of

Runoff

Figure 3. Naturalized Columbia River streamflow at The Dalles (dashed) and in 2050, as simulated by several climate models. The blue band indicates the upper and lower bounds of projected average streamflow in the 2050s. Note the higher winter flows, reduced spring/summer flows, and the shift in the timing of peak spring flows earlier into the spring season. The effects of the Columbia River dams on streamflow have been removed.

CWG, UW

1. winter flow

2. summer flow

3. earlier peak flow

More Rain, Less SnowReduced Snowpack

South Cascade Glacier, Washington Cascades

1928

1966

2006

53 North Cascade glaciers gone since the 1950s

Glacier Melt

ALSO: Glacier National Park

Impact of Global Warming on FuturePacific Northwest Water Resources

(part 1)

• probable modest in precipitation

• more rain, less snow• increased evapotranspiration• reduced snowpacks• higher and earlier flood peaks

Milder Winters & Hotter Summers

Oct. – March should be wetterApril – Sept. uncertainJune & July possibly drier

Impact of Global Warming on FuturePacific Northwest Water Resources

(part 2)

• increased intensity of precipitation: more extreme events• reduced water availability in summer (peak irrigation demand)• less power generation• more difficult fish migration in lower-flow rivers

MORE FLOODS . . . MORE WATER SCARCITY

New York TimesDec. 5, 2007MORE FLOODS

Changes in frequency of extreme precipitation, 1948-2006

Centralia, Washington on December 5, 2007

MORE FLOODS

Barnett et al., 2008, Science Magazine

Barnett et al., 2008, Science Magazine

(there is) “a coming water crisis in the Western United States.”

Proposed Black Rock Dam, Yakima County

Columbia River Storage Options Study, June 2007

#1 site: Lower Crab Creek

MORE WATER SCARCITY

1

2

21 11 7 4

To recap, what can we expect in the PNW?• temperature by 2100 of 2-10F

best guess: 0.5F / decade . . . 5F by 2100

• milder winters, hotter summers

• more rain, less snow• more extreme precipitation events• reduced snowpack• disappearing glaciers

• higher and earlier flood peaks• increased water scarcity• urban / rural water conflicts• more calls for water conservation • more calls for taxpayers to build new dams

All against a background trend of steady population growth

“We’re headed for a train wreck” (Tim P. Barnett, Scripps Institution of Oceanography)

New York TimesJanuary 8, 2008

• Greenland could be gaining snow and ice in the interior• Greenland is losing ice at its edges• Net change: transfer of H2O from ice sheet to oceans

South Cascade Glacier,Washington Cascades

1928

1966

2006

Figure 3.13. Trend of annual land precipitation amounts for 1901 to 2005 (top, % per century) and 1979 to 2005 (bottom, % per decade), using the GHCN precipitation data set from NCDC. The percentage is based on the means for the 1961 to 1990 period. Areas in grey have insufficient data to produce reliable trends. The minimum number of years required to calculate a trend value is 66 for 1901 to 2005 and 18 for 1979 to 2005. An annual value is complete for a given year if all 12 monthly percentage anomaly values are present. Note the different colour bars and units in each plot. Trends significant at the 5% level are indicated by black + marks.IPCC, 2007

Increased Global Precipitation (Past)

105 years

26 years

Figure 10.12. Multi-model mean changes in (a) precipitation (mm day–1), (b) soil moisture content (%), (c) runoff (mm day–1) and (d) evaporation (mm day–1). To indicate consistency in the sign of change, regions are stippled where at least 80% of models agree on the sign of the mean change. Changes are annual means for the SRES A1B scenario for the period 2080 to 2099 relative to 1980 to 1999. Soil moisture and runoff changes are shown at land points with valid data from at least 10 models. Details of the method and results for individual models can be found in the Supplementary Material for this chapter.

FAQ 5.1, Figure 1. Time series of global mean sea level (deviation from the 1980-1999 mean) in the past and as projected for the future. For the period before 1870, global measurements of sea level are not available. The grey shading shows the uncertainty in the estimated long-term rate of sea level change (Section 6.4.3). The red line is a reconstruction of global mean sea level from tide gauges (Section 5.5.2.1), and the red shading denotes the range of variations from a smooth curve. The green line shows global mean sea level observed from satellite altimetry. The blue shading represents the range of model projections for the SRES A1B scenario for the 21st century, relative to the 1980 to 1999 mean, and has been calculated independently from the observations. Beyond 2100, the projections are increasingly dependent on the emissions scenario (see Chapter 10 for a discussion of sea level rise projections for other scenarios considered in this report). Over many centuries or millennia, sea level could rise by several metres (Section 10.7.4).

Figure 3.15. Latitude-time section of zonal average annual anomalies for precipitation (%) over land from 1900 to 2005, relative to their 1961 to 1990 means.

IPCC, 2007

Past Precipitation Trends, by latitude

IPCC, 2007

USA USA

USAUSA

FAQ 11.1, Figure 1. Blue and green areas on the map are by the end of the century projected to experience increases in precipitation, while areas in yellow and pink are projected to have decreases.

Increased Global Precipitation

(Projected to 2100)

FAQ 6.1, Figure 1. Schematic of the Earth’s orbital changes (Milankovitch cycles) that drive the ice age cycles. ‘T’ denotes changes in the tilt (or obliquity) of the Earth’s axis, ‘E’ denotes changes in the eccentricity of the orbit (due to variations in the minor axis of the ellipse), and ‘P’ denotes precession, that is, changes in the direction of the axis tilt at a given point of the orbit. Source: Rahmstorf and Schellnhuber (2006).