Transcript Lecture 6 and 7 (easy print)

Daytime
Night
Source: Ahrens, 2001
Mountain Valley Breezes
Daytime
The sun heats the
hillslope, causing
air to move up the
slope
Night
Night radiation cools
the slopes
Cooler, denser air
moves downslope
Source: http://apollo.lsc.vsc.edu
Katabatic Winds
•Air cools on a plateau or sloping terrain, becomes
more dense and descends
•Winds get faster and faster downslope
•Relatively warm water at base can further increase
winds, which can be very strong as a result
•Can occur on large scale (eg. Greenland, Antarctica)
•Also referred to as gravity drainage winds
Chinook Winds
Cooling
At MALR
6°C/km
Cooling
At MALR
6°C/km
X
VANCOUVER
8°C
Warming
At DALR
10 °C/km
Warming
At DALR
10 °C/km
Cooling
At DALR
10 °C/km
X
LETHBRIDGE
12°C
More sensible heat
Effect of Air temperature on 500 mb heights
Source: http://apollo.lsc.vsc.edu
Geostrophic winds
Wind flows along isobars
PGF counterracted by inertial CoriolisForce
(see any 500 mbar height map)
Weather vs. Climate
•Weather
Condition of the atmosphere at any place and time
http://weatheroffice.ec.gc.ca/forecast/city_e.html?yql
•Climate
Characteristic behaviour of weather over time
Includes averages and extremes
http://www.theweathernetwork.ca/weather/stats/pages/C02080.htm?CAAB0194
Climatology is the study of climate
Climatic regions: zones with characteristic weather patterns
Empirical (statistics) or genetic (causative) classification
Eg. Köppen-Geiger Climate Classification System (1928)
Climographs
200
Precip
180
20
Temp
15
140
120
10
100
5
80
60
0
40
-5
20
0
-10
160
Precipitation (mm)
Precipitation (mm)
160
200
25
Temperature (degrees C)
180
VANCOUVER, BC
25
Precip
20
Temp
15
140
120
10
100
5
80
60
0
40
-5
20
0
-10
J F M A M J J A S O N D
J F M A M J J A S O N D
Month
Month
Temperature (degrees C)
LETHBRIDGE, AB
Determinants of climate:
•Distribution and seasonal variation of solar insolation intensity
(zenith angles and daylength)
•Atmospheric and oceanic global circulation patterns
•Controls of temperature: altitude and latitude, land-water
heating differences, cloud cover, polar front
•Controls on precipitation: distribution of pressure systems, lift
mechanisms (convergence, convection, orographic, frontal),
location of ITCZ, subtropical high pressure, jet streams
Effect of Altitude
Source: Solomon, 2000
Effect of Latitude and Cloud Cover
Solar insolation is reduced with
latitude or cloud cover
Global Circulation
Patterns
Climate Distribution
Classification systems: Köppen-Geiger, Thornthwaite (not shown)
A
C
D
E
Tropical - equatorial regions
Mesothermal – eg. Mediterranean, marine W. coast
Microthermal – eg. humid continental, subarctic
Polar
H
B
Highland – cooler than surroundings
Dry – deserts and steppes
See Figure 6-4
A
Tropical Climates
Straddle equator: 20N to 20S
Coldest month is above 18C
Consistent daylength, small zenith angles
Includes tropical rainforest, tropical
monsoon and tropical savanna
1. Tropical Rain Forest Climate
•Warm and moist
•Thunderstorms – local convection in convergent ITCZ
•All months receive more than 60mm
•Precipitation pattern follows migration of ITCZ
•Two wetter seasons near equator, one wetter season near tropics
•High rainfall and solar insolation sustain lush, evergreen,
broadleaf tree growth
•High leaf area index (LAI)
•Dark canopy floor with sparse vegetation
•Rapid decomposition – more nutrient mass in vegetation than soil
Rainforest Climograph
Manokwari, New Guinea
Little variability in
average monthly
temperature
Driest month receives
more than 100 mm of
rainfall
Source: http://www.geocities.com/Athens/Parthenon/1020/biome.html
Tropical Rain Forest Vegetation
Layers in the Tropical Rain Forest Canopy
Source: http://www.world-builders.org/lessons/less/biomes/rainforest/tropi_rain/tropgifs
Layers in the Tropical Rain Forest Canopy
Emergents
•Trees “emerge” from the forest canopy
•Exposed to high light, fluctuating temperatures, higher
winds
•Huge trees (up to 70m) with massive, buttressed trunks
•Seed dispersal often by wind
•Home to many birds and animals looking for safety from
predators (eg. eagles, bats, monkeys, snakes, butterflies)
•Buttressed trunks to support weight of tree, water and
epiphyte biomass
Canopy Layer
•Continuous layer (about 45 m)
•Most have buttressed trunks
•Especially high diversity of plants and animals
•Same tree found once or twice per square kilometre
•Lianas (vines) connect trees
•Epiphytic vegetation common -28,000 species (eg. mosses,
bromeliads, ferns, orchids)
•Abundant fauna (eg. monkeys, sloths, bats, treefrogs, ants,
beetles, parrots, hummingbirds and snakes)
Understorey Layer
•Receives 2-5% of incident light (blocked by canopy)
•Understorey plants photosynthesize most efficiently
under low light (low respiration rates)
•Layer consists of small trees (eg. dwarf palms) and
seedlings of taller trees
•Low wind: insect pollination, strong smelling and
conspicuous flowers often on trunks
•Abundant fauna (eg. insects, snakes, frogs, parakeets,
leopards, jaguars etc.)
Forest Floor
•Approximately 1% of light incident upon the canopy
•100% relative humidity, less temperature variation
•Rapidly-decomposing organic matter
•Few flowering plants
•Fungi thrive on decomposing organic matter
•Large mammals forage for roots and tubers (eg. tapirs)
•Many insects (eg. termites, cockroaches, beetles,
centipedes, millipedes, scorpions and earthworms)
Deforestation
•>50% already gone (pasture, timber, fuelwood, farming)
• Approximately 169,000 km2 lost each year
• Fire clears land for agriculture (food production, rubber,
coffee etc.)
• Slash and burn – soil nutrient reserves quickly exhausted
• Destruction generally along transportation networks
• Tropical Forestry Action Plan (FAO, UNDP, WB, WRI)
• Remote sensing and GIS play key role in monitoring
2. Tropical Monsoon and Savanna Climates
Tropical Monsoon Climates
•Rainfall from ITCZ affects regions for 6-12 months of the
year (eg. text example Yangon, Myanmar)
•Seasonal variation in winds and precipitation
•1 or more months have less than 60mm of precipitation
•Evergreen broadleaf trees grade toward thorn forests along
drier margins with savanna
Tropical Monsoon Climograph
Dry season
during the
Northern
Hemisphere
winter
Wet season
during the
summer
Tropical Savanna Climates
•ITCZ effect for <6 months of the year
•Winters are dry (subtropical high pressure)
•Summers are wet (influence of ITCZ)
•Tropical cyclones possible near east coasts
•Grasslands dominate: scattered, drought-resistant trees
•Text example: Mérida, Mexico (relatively wet) and Kenya
Tropical Savanna Distribution
Savanna Climograph
Long dry season during
the Southern Hemisphere
winter
Wet season during the
summer
http://www.cotf.edu/ete/modules/msese/earthsysflr/savannah.html
Vegetation in the Tropical Monsoon and
Savanna Climate Zones:
Tropical Seasonal Forest and Scrub
•Poleward transition from tropical rain forest to
grasslands
Monsoonal forestsopen woodlandsscrub
woodlandthorn forestsdrought-resistant
scrubgrassland
•Leaf loss and dry season flowering during seasonal
moisture deficits
Monsoonal forests:
•Discontinuous, 15 m high canopy
•Denser undergrowth
•Orchardlike parkland with grassy openings in drier sectors
•Flat-topped acacia trees become common in drier zones
•Examples: Caatinga (Brazil), Chaco (Paraguay), Brigalow
(Australia), Dornveld (S. Africa)
•Wildlife: elephants, large cats, rodents, ground-dwelling birds
•Koalas and cockatoos in Australia
Monsoon Forest of India
Increased light penetration
compared to lowland rain forest
Discontinuous canopy and lower
LAI
Vegetation of the tropical savanna
•Large expanses of grassland, interrupted in areas by trees
and shrubs
•Trees and shrubs are xerophytic (small, waxy, thick leaves)
•Most expansive in Africa (Serengeti plains, Sahel)
also Los Llanos (Venezuela), Campo Cerrado, Pantanal (Brazil)
•Fires common during the dry seasons (beneficial if early)
•Affected by desertification
•Soils richer in humus than tropical rain forests: sorghum,
wheat, peanuts can be grown
•Home to large land mammals in Africa: lion, cheetah, zebra,
giraffe, buffalo, gazelle, wildebeest, antelope, rhinoceros and
elephant
Interannual climatic variability at
the global scale
Caused by changing atmospheric and
oceanic circulation in the tropical
Pacific Ocean
See http://www.cdc.noaa.gov/map/clim/sst_olr/sst_anim.shtml
C Mesothermal Climates
1. Humid Subtropical Hot Summer Climate
•Influenced by maritime tropical air masses in summer
•Continental polar and maritime tropical air masses mix in
fall/winter/spring: frontal precipitation
•Convectional precipitation in moist, unstable summer
airmass
•Tropical cyclones near coasts in summer and fall
•1000 – 2000 mm/yr total
•Examples: southeast U.S., southeast China, southern Japan,
northern Argentina
•Broadleaf and mixed forest
2. Humid Subtropical Winter Dry Climate
• Similar to above, but dry in winter
• Heavy precipitation in summer
• Circulation in winter prevents moist, tropical air mass
interaction with pressure systems
eg. much of southern China, eastern South Africa
• Broadleaf and mixed forest, but largely deforested
(see Figure 6-11)
3. Marine West Coast Climates
•Mild winter and relatively cool summer
•Winter maximum of precipitation, especially in southern zones
•Heavy precipitation in mountains (may exceed 4000 mm/yr)
•Precipitation varies at low altitude: much more precipitation in
northern portions of the Marine West Coast Climate than in the
south
•Dominated by maritime polar air masses but unusually mild for
their latitudes
•Coastal fog is common
Temperate Rain Forest
•Narrow margin of Pacific NW North America
•Less species diversity than TRF
•Needle/broadleaf trees, ferns and undergrowth
•Tallest tree in world (Sequoia sempervirens –
Redwood) may exceed 100m
•Also Douglas Fir, Spruce, Cedar, Hemlock
•Moist, lush vegetation
•Fauna: Bear, badger, deer, wild pig, wolf,
bobcat, fox and numerous bird species
4. Mediterranean Dry Summer Climates
•Poleward of subtropical high pressure on west coasts
•Subtropical high prevents precipitation and influx of
tropical moist air in summer
•At least 70% of precipitation occurs in the winter
•Summer water resource problems
•Agriculture requires irrigation
•Hot summer and cool summer varieties
•Cool offshore currents enhance stability of marine air
mass along west coasts
Examples: Mediterranean, southwest California,
northwest coastal Mexico, central Chile, southern tip of
South Africa
Mediterranean Shrubland: “Chaparral”
•Sclerophyllic shrubs
Short-statured, deep roots,
leathery leaves, low branches
Grass between shrubs
•Fire adaptation
Resprouting capability
Cork Oak, Pine and Olive trees
in Mediterranean
Commercial agriculture: fruits,
vegetables and nuts
Fauna: deer, coyote, wolf, bobcat, rodents and birds
D Microthermal Climates
Temperature variation is high due to season and air masses
1. Humid Continental Hot Summer Climate
•Frequent passage of pressure systems
•Maritime tropical air masses and convection influence climate
in summer
•Occasional intrusion of cold, polar air in winter
•Some areas have a dry winter, but others have similar year-round
precipitation totals. Why ?
Influence of coastal storms or lake effect snows in winter
•Corn, soybean, hog and cattle farming without irrigation
•Midlatitude broadleaf and mixed forest
See New York City Climograph (Figure 6-15)
2. Humid Continental Mild Summer Climate
•Precipitation is generally lower than in the hot summer climate
•Temperature is cooler than in the hot summer climate
•Snowmelt in winter important for soil moisture recharge
•Winter is relatively dry except near lakes and oceans
Agriculture: includes dairy cattle, poultry, flax, sunflowers, sugar beets,
wheat and potatoes (usually without irrigation)
•Midlatitude broadleaf and mixed forest tending to needleleaf forest to
north on shallower soils
Examples: Great Lakes, much of northeast Europe
(See Moscow climograph – Fig 6-16)
Midlatitude Broadleaf and Mixed Forest
•Very productive in summer, senescence in fall
•High LAI, limited undergrowth in old growth forest
Trees: Maple, Oak, Beech, Elm, Chestnut in Great
Lakes, New England and Maritimes, mixed with White
Pine, Red Pine and Eastern Hemlock
Fauna: Red fox, white-tailed deer, southern flying
squirrel, opossum, bear and a great variety of birds (eg.
cardinal, blue jay)
3. Subarctic Climates
•Very long, cold winters – dominated by high pressure
•Discontinous or continuous permafrost at high latitude
•Boreal forests or Taiga where growing season sufficient
Fir, Spruce, Larch and Birch
•Open northern woodlands and tundra in far north
•Winters are generally drier than summer
However, the Dry Winter form of subarctic climates occurs only
in Russia
Bitter cold occurs in these areas in winter
Verkoyansk has an average 63C temperature range
Climograph: Subarctic climate
Low precipitation
and cold
temperatures in
Winter
Huge temperature
range
Needleleaf forest and Montane Forest
•Boreal forest from Alaska, across northern portions of AB, SK,
MB, ON, QC to east coast of Newfoundland and Labrador
•Taiga from European plain across much of Russia through
Siberia
•Only extensive in N. hemisphere, but occur at montane sites in
S. Hemisphere
Trees: Pine, Spruce and Fir
Fauna: wolf, moose, bear, lynx, beaver, wolverine, small
rodents, hawks, eagles, grouse, owls and migratory birds
4. Tundra Climate
•8-10 months of snow
•Generally underlain by permafrost
Vegetation:
Stunted sedges, mosses flowering plants and lichen in brief summer
Most rapid climate warming is in this zone
Only in northern hemisphere, except in highlands
Arctic tundra
Light and heat may not be the only limiting factors for
plant growth
•Days are long and temperatures may reach the teens in
summer
Wind and moisture deficit are also important
•Thin, active layer holds limited moisture. Small, leathery
leaves, closely spaced to protect stomata
•Hairs limit air circulation
•Flowers are small
•Plants often occur in tufts for protection
•Prostrate growth - stems spread out over ground with little
vertical growth - especially willow
Climograph: Tundra Climate
Low Arctic Tundra
•Extends north from treeline along a line from Northern Alaska to
northern Quebec and southern Baffin Island (10 degree C isotherm)
•Cold, with low precipitation
•Nearly the entire area is underlain with permafrost
•Almost complete vegetation coverage (except unfavourable areas)
•Dominated by dwarf shrubs (birch and willow)
•Vegetation traps snow and provides shading from summer heating
•Peat accumulation at poorly-drained sites
•Any black spruce is very stunted and abraded by snow
•Major summer range and calving grounds of some of Canada's largest
caribou herds
Mid Arctic Tundra
•Transitional band between high and low arctic
•Plant cover more than 50% in most areas but bare ground still exists
locally
•Vascular plants more common than in high arctic - willow common
High Arctic Tundra
•<50% vegetation coverage
Wetland Environments
•Cover 14 to 18% of Canada
•Mainly just to the south of treeline in discontinuous and
sporadic permafrost
•Pockets further north
•Major carbon sink
•Potential future source of greenhouse gases
•Hydrophyllic vegetation present due to water table at or
above mineral soil
Source: Natural Resources Canada
http://atlas.gc.ca/english/facts/wetlands/wetlands_ewetdist2_e.html
Bog
•
•
Sphagnum moss dominated
Receives nutrients only from precipitation
Fen
•
•
A peatland receiving nutrients from mineral soil below
Flora is more abundant and diverse, including sedges, grasses,
shrubs and even trees (tamarack)
Swamp
•
•
•
A wooded wetland
May develop into a peatland
Coniferous and deciduous trees, shrubs, herbs and mosses
Marsh
•
•
Periodically inundated wetland (fresh or salt water)
Little peat accumulation
Why does peat accumulate ?
•Production by plants exceeds decomposition
•Abundant growth due to available moisture during
growing season
•Preservation of plants (cool conditions)
•Saturated conditions - slow, anaerobic decomposition by
methanogenic bacteria
•Release of methane rather than CO2
5. Ice Cap Climate
•Dominated by dry, frigid air masses
•Average temperature below freezing most or all year
•World’s coldest surface air is found in Antarctica in S.
hemisphere winter
•Glaciers accumulate snow and ice despite low precipitation
(<80mm/yr in Antarctica)
•Precipitation exceeds small evapotranspiration demand
Examples: Antarctica, North Pole, Greenland
Climograph: Ice Cap Climate
B Desert and Semiarid Climates
Vegetation is xerophytic
Phreatophytes along stream channels
Subtropical dry climates
•Subtropical high pressure cells dominate
•Stable air, low relative humidity
•Extend to western continental margins from 15 to 30N
•Cool stabilizing ocean currents
The Rain Shadow effect
•Orographic lift over western mountains and subsequent descent
of air
•Extends along eastern edge of Andean and Rocky mountains
north of 30N
1. Hot Low Latitude Desert Climate
•0 to 350 mm precipitation
•Western side of continents in subtropical high zone
•Also Egypt, Somalia and Saudi Arabia
2. Cold Midlatitude Desert Climate
•Approx. 150 mm precipitation
•Gobi Desert, southern countries of former USSR, Patagonia
•Any precipitation due to summer convection
Distribution of Earth’s Deserts
Desert Biomes
•>1/3 of Earth’s land area
•Ephemerals (wait a year or more for precipitation)
Seeds quickly germinate, plants develop, flower, and produce
seeds
•Long, deep tap roots (eg. mesquite), succulence (thick, fleshy,
water holding tissue), waxy coatings and fine hairs on leaves to
retard water loss, leafless conditions during dry periods
Fauna:
Desert bighorn sheep, camel, kangaroo rat, lizards, scorpions,
snakes are active at night, when temperatures are lower.
Birds include roadrunner, thrashers, ravens, wrens, hawks and
grouse
3. Hot Low Latitude Steppe Climate
•Around periphery of hot low latitude desert
Eg. northern Sahel, parts of Iran and Afghanistan, Turkistan and
Kazakhstan
4. Cold Midlatitude Steppe Climate
•Occur poleward of 30 latitude, mainly in northern hemisphere,
in areas distant from major moisture source or rainshadowed
•Widely variable, undependable precipitation (200 – 500
mm/yr)
•Cyclonic storms occur, but precipitation tends to be light
•Summer convection produces much of year’s precipitation
Midlatitude Grasslands
•The world’s breadbasket – grain and livestock production
•Heavily modified by human activity (few natural sites)
•Good soil quality
•Only trees are deciduous broadleaf, along streams
•Shrubs in protected areas
•Tall-grass prairie once rose to 2m, with short grass steppe
further west
Fauna: deer, antelope, pronghorn, bison, gophers, prairie dogs,
coyote, badger, hawks, eagles, owls, grasshoppers
Look out the window !