Urban Climate

Climate October 22, 2012

Lecture learning objectives: You should be able to: • Describe the difference between climate and weather • Describe major climate factors –

-radiation, albedo, energy budgets, wind and atmospheric circulation, temperature, and moisture.

• Explain the differences between urban and forest microclimates and what drives those differences. • Identify indicators of climate change

Micro, meso, macro and megaclimate Scale

Length

Area

Locale

Micro

1 m - 1 km

1m² - 1 km²

local

Meso

1 - 100 km

1 - 100 km²

regional

Macro

100 - 10 000 km

100 - 10 000 km² continental

Mega

>10 000 km

>10 000 km²

global

What is the difference between weather and climate? • Climate is what you expect • Weather is what you get

Climate factors • Radiation and albedo • Energy budgets • Wind – global circulation, high and low pressure systems • Temperature – effects of latitude and elevation, greenhouse effect • Moisture – types of precipitation, seasonal distribution, latitudinal distribution, orographic precipitation

Ecosystems use solar energy to drive processes • < 2 % of solar energy is used for photosynthesis • Most goes into evaporating water. • Heat balance, hydrologic cycle and climate are strongly linked. • Forests have 70% of leaf area on the Earth.

Radiation and albedo • Forms of radiation Ultraviolet, visible, infrared (heat) short wave long wave

http://serc.carleton.edu/images/eslabs /weather/balance_diagram_simple.jpg

www.windows.ucar.edu/earth/Atmosphere/images/...

Albedo Proportion of shortwave radiation that is reflected (0-1 scale) Albedos of different surfaces Vegetation type Albedo Temperate forest (summer) 0.12 (winter) 0.25 Tropical forest 0.07 Savanna 0.16 Field, grassland 0.16 (summer) Desert 0.35 Ocean ice 0.5-0.7 Asphalt 0.04-.12 Color of the surface is important – white surfaces have the highest albedos – dark surfaces (black) have the lowest albedos

Species have different leaf strategies with respect to radiation • Species adjust leaf areas to capture light or handle heat loads. • western hemlock (shade tolerant) has greater leaf area (m2 leaf/m2 of surface) than Douglas-fir (shade intolerant). • Species like Noble fir have sun and shade needles. • Eucalyptus leaves are vertical to reduce heat load in a hot environment.

http://www.nps.gov/neri/naturescience/images/web_HWA_01.jpg http://t1.gstatic.com/images?q=tbn:ANd9GcRcUJDJPOFyMWtGLbA-DNCe0QgQX7IC4Hw-mnLvdigIDHtZDFCUAxYAyNafZQ http://www.cirrusimage.com/Trees/Eucalyptus_leaves.jpg

Global wind and circulation patterns

Broadly predicts global to continental climate

Nasa.gov

Local winds

Santa Ana Winds

USA Today

Mountain valley winds

http://t3.gstatic.com/images?q=tbn:ANd9GcTRZqSuMV9Rkd9MIIk-FqKXpexuhgPVn8Fiy0O1arw0od_gmz2rP778sCCH

Urban canyons (valleys) Urban structure also affects winds, albedo and radiation

http://en.wikipedia.org/wiki/File:42nd_st_canyon.jpg

TEMPERATURE INVERSIONS

Ag.arizona.edu

http://www.stuffintheair.com/images/Inversion_Smoke.jpg

apollo.lsc.vsc.edu

Temperature Global temperatures are highest in tropics and lowest at the poles Lowest at highest elevation

Temperature at noon on field trip Oct 13, 2012 46 F Stampede Pass 3965 feet

58 F Seattle 100 feet

64 F Ellensburg 1764 feet

Moisture – humidity and precipitation Precipitation tends to be highest in tropics and lowest at the poles Modified by mountain ranges that produce orographic rainfall on the windward side of mountains and rain shadows on the lee side of mountains

http://www.whymap.org/whymap/EN/Downloads/Additional_global_maps/precipitation_g.jpg?__blob=normal&v=3

3. Urban and Forest Microclimates • Forest and urban trees modify the climate because of albedo and energy budgets. • Trees cool the environment (low albedo, high evapotranspiration, low sensible heat) • Concrete and dark asphalt surfaces heat the environment (high albedo, no transpiration, low evaporation, high sensible heat. The urban heat island effect

Clearcuts are hotter and colder than forests. South slopes, particularly SW slopes are hotter and drier than north slopes. Steeper slopes are hotter.

www.arch.hku.hk

Mitigation of Urban Heat Islands • Increase vegetative cover • Use porous concrete surfaces • Change the albedo of surfaces

PNW weather and climate are dominated by two elements: Pacific Ocean to the west Mountain ranges that block and deflect

24

Average Rain Per Year • Seattle: 37” • New York City: 47” • Miami: 56”

Number of Cloudy Days Per Year Seattle: 228 (61%) Houston: 166 Miami: 117 (31%) 25

East vs West Cascades • Annual temperature range – East side: varies by 60ºF between Jan-July – West side: varies by 30ºF

• Precipitation range – I-84 along Columbia River gorge: Rain forest near Cascade Locks (80”/year) to arid environment near The Dalles (13”/year) in just 45 miles

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Most temperate forests are dominated by broad-leaved deciduous trees • If enough water to support trees vs grasses • Dormant during winter • New leaves in spring • Photosynthesis in wet summer

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PNW Ecosystems Why do conifers dominate here? • Short, cool summers • Mild winters • Precipitation mostly in winter (75% between OctMar) • Dry summers

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Photosynthesis and Water Conservation are opposites. The Photosynthesis-Transpiration Compromise: must open stomata to bring in CO2 but in so doing, the plant loses water vapor

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The PNW west-side Challenge • • • •

Optimum photosynthesis: warm and bright PNW is warm and bright mid-July to mid-Sept * These are the driest months * Regulate stomatal opening to reduce water loss during drought conditions • Lose best opportunity for photosynthesis

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Solution? Retain leaves and do photosynthesis whenever possible

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West  East

• Precipitation drops off rapidly east of the passes • Droughttolerant pines and junipers • Grassland and desert 33

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Global Climate Change • Thin layer of atmosphere traps some of the Sun’s energy and heat • Problem = Thickening layer (“Greenhouse gases”) • Average global temperatures are rising

Instrument Data (thermometer records)

Global mean surface temperature anomaly 1850 to 2006 relative to 1961–1990

Hotter than normal globally • Hottest years on record in USA: 1934, 1998, and 2006 • Red=warmer than average • 1934: hot in some areas; 1998 & 2006: globally hotter

Departure from normal temperatures

Image credit: U.S. Global Change Research Program (www.globalchange.gov).

Past warming trends • From 1000-2000: 3 little blips (3 between 1000-1400 A.D.) before current trend • Shorter duration and smaller magnitude

Indications of Global Climate Change 1. Glaciers are melting 2. Heat waves 3. Ocean temperature is rising 4. More powerful storms 5. Increased flooding 6. Drought (relocalization of precipitation) 7. Melting ice caps 8. Melting tundra 9. Tropical plants moving north 10. Insect infestations 11. Sea level is rising And more

1. Glaciers are melting 1928

2004

Upsala Glacier in South American Andes in Argentina - Retreating 180 feet per year

• The total surface area of glaciers worldwide has decreased by 50% since the end of the 19th century

What controls glacier changes? Accumulation (snowfall, rainfall) Temperature (summer/winter)

Dr. Michelle Koutnik (UW PhD ‘07)

2. Heat waves • Heat wave in Europe 2003- killed 35,000 • Record-breaking heat in 2005 in many American cities – Hottest and longest duration above 100F

• Of the 21 hottest years on record (global), 20 within last 25 years

3. Ocean temperature is rising • Cannot get the long history of temperature data • Warming trend • Since 1960’s, more warm temperature anomalies

4. More powerful storms • Increased frequency – 2004: Japan’s typhoons (10) – U.S. severe hurricanes (Katrina) – 2005: First time World Meteorological Society ran out of names (27)

4. More powerful storms (cont.) • Unusual places – 2004: first hurricane in Brazil

• Previously thought impossible in South Atlantic

Power of hurricanes correlates with sea surface temperature

5. Increased flooding 350

Number of Major Flood Events

300 250 200

Europe Americas Asia

150 100 50 0

19501959

19601969

19701979

Source: Millennium Ecosystem Assessment

19801989

19902000

6. Relocalization of precipitation • Global precipitation increased by 20% in last century • But not evenly distributed • Severe droughts

Changes in precipitation • Amount, intensity, frequency, and type • More in E North America, S South America, N Europe • Less in Mediterranean, Africa, and S Asia • More rain and less snow in mountains

7. Melting ice caps • Antarctica- frozen desert • Losing land ice at rate of 31 billion tons of water per year • Ice shelves are breaking up • Emperor penguin population declined 70% in last 50 years – Depends on stable sea ice

8. Melting Tundra • Western Siberia is thawing for the first time in 11,000 years • Size of France + Germany • Started to thaw only recently • Western Siberia temp increasing faster than anywhere else

9. Subtropical plants moving North • Overwintering plants that normally don’t survive • Subtropical camellias in Pennsylvania • Kudzu (fast-growing vine) moving north • State Flowers of 28 states soon can’t grow there

9. Plant zones are changing (cont.) • Gardening maps are changing – Many areas are a full zone warmer – Some are two zones warmer than in 1990

10. Insects • Beetles wiping out forests in Canada – Pine beetles kept in check by cold – 14 million acres of bark beetle-infested spruce trees

11. Sea level is rising • • • •

2000 years of little change Rose 8” in last 100 years Water expands as it warms Melting glaciers and ice sheets

http://climate.noaa.gov/warmingworld/docs/WarmingWorldInteractive-04062012.ppt

Figure from NASA.gov

Climate Change in the PNW? • Local simulations: – largest warming on lower and middle mountain slopes – More cloudiness in spring in west side – More rain and less snow

Impacts of these changes? 64

The 2007 IPCC report Conclusions • “Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level.” • Eleven of the last 12 years (1995-2006) rank among the 12 warmest years in the instrumental record since 1850.

West Olym pic Coastal Division, Washington Tem perature(C) Climate Division (01), 12 month period ending in December 12 month period

11 Tem perature (C)

10 year running mean 10

average +sigma

9

-sigma 8 1890

1900

1910

1920

1930

1940

1950

1960

1970

1980

1990

2000

Ending Year of Period

Cascade Mountains West Division, Washington Tem perature (C) Climate Division (05), 12 month period ending in December 12 month period

Temperature (C)

10 9

10 year running mean

8

average

7 6

-sigma

5

+sigma

4 1890

1900

1910

1920

1930

1940

1950

1960

Ending Year of Period

1970

1980

1990

2000

Temperature trends – WA, ID WA

ID

Modeled predicted species changes • Ponderosa pine will expand, Douglas-fir and lodgepole pine will increase range • Tree line in mountains will be much higher – shrinking alpine zone. Engelmann spruce, Mt. hemlock and Pacific silver ranges will be reduced. • Some desert species will expand

Lecture learning objectives: You should be able to: • Describe the difference between climate and weather • Describe major climate factors –

-radiation, albedo, energy budgets, wind and atmospheric circulation, temperature, and moisture.

• Explain the differences between urban and forest microclimates and what drives those differences. • Identify indicators of climate change