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Global Climate Systems and Biomes
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Weather vs. Climate Weather Climate
Weather Condition of the atmosphere at any place and time Climate Characteristic behaviour of weather over time Includes averages and extremes 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)
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Climographs LETHBRIDGE, AB VANCOUVER, BC
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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
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Effect of Altitude Source: Solomon, 2000
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Effect of Latitude and Cloud Cover
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Global Circulation Patterns
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Climate Distribution A Tropical - equatorial regions
Classification systems: Köppen-Geiger, Thornthwaite (not shown) A Tropical - equatorial regions C Mesothermal – eg. Mediterranean, marine W. coast D Microthermal – eg. humid continental, subarctic E Polar H Highland – cooler than surroundings B Dry – deserts and steppes See Figure 6-4
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A Tropical Climates Straddle equator: 20N to 20S
Coldest month is above 18C Consistent daylength, small zenith angles Includes tropical rainforest, tropical monsoon and tropical savanna
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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
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Rainforest Climograph Manokwari, New Guinea
Little variability in average monthly temperature Driest month receives more than 100 mm of rainfall Source:
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Tropical Rain Forest Vegetation
Layers in the Tropical Rain Forest Canopy Source:
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The Tropical Rain Forest
The world’s most biologically-diverse biome
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Layers in the Tropical Rain Forest Canopy Emergents
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)
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Buttressed Trunks Helps support large tree biomass,
weight of water and epiphytes
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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)
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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.)
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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)
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Global Distribution of Tropical Rain Forests
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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
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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
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Tropical Monsoon Climograph
Dry season during the Northern Hemisphere winter Wet season during the summer
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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
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Tropical Savanna Distribution
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Savanna Climograph Long dry season during the Southern Hemisphere
winter Wet season during the summer
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Vegetation in the Tropical Monsoon and Savanna Climate Zones:
Tropical Seasonal Forest and Scrub Poleward transition from tropical rain forest to grasslands Monsoonal forestsopen woodlandsscrub woodlandthorn forestsdrought-resistant scrubgrassland Leaf loss and dry season flowering during seasonal moisture deficits
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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
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Monsoon Forest of India
Increased light penetration compared to lowland rain forest Discontinuous Canopy and Lower LAI Source: I. de Borhegyi FAO
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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
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The Serengeti Plain (Savanna)
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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
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Examples: southeast U.S., southeast China, southern Japan,
northern Argentina Broadleaf and mixed forest Source: M.K. House, near Tallahassee, Fl.
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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)
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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
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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 Source:
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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
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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 Source: F. Tanaka Source: S. Johnson, U. California, Berkeley
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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)
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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)
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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)
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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 63C temperature range
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Climograph: Subarctic climate
Low precipitation and cold temperatures in Winter Huge temperature range
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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
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South Knife Lake, Manitoba, Canada
Photograph by Lynda Dredge (GSC, Natural Resources Canada)
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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
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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
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Climograph: Tundra Climate
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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
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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 Cumberland Sound, Baffin Island, Nunavut, Canada Photograph by Govt. of the Northwest Territories
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Arctic Willow Photo: JoAnn Elliott Denali National Park
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Arctic willow
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High Arctic Vendom Fiord, Ellesmere Island, Nunavut, Canada
Photograph by Douglas Hodgson (GSC, Natural Resources Canada)
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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
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Source: Natural Resources Canada
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Bog Fen Swamp Marsh 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
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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
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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
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Climograph: Ice Cap Climate
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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 30N 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 30N
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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, US southwest, Patagonia Any precipitation due to summer convection
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Distribution of Earth’s Deserts
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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
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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
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Midlatitude Grasslands
The world’s breadbasket – grain and livestock production Heavily modified by human activity (few natural sites) Good soil quality Only trees are broadleaf trees 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 !
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What a terrible scale interval !
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