Chapter 8: Climate and Climate Change – p. 1 of 15
Chapter 8: Climate and Climate Change
I. Climate Classification
A. Intro
1. basic goal of the geographic study of climate: understand its distribution over Earth
2. challenges: climate involves continuous variation and can change over time
B. Early Classification Schemes
1. ancient Greek system – 3 climate zones
a. Temperate Zone of the midlatitudes (Athens @ 38oN)
b. Torrid Zone of the tropics to the south
c. Frigid zone to the north
C. The Köppen Climate Classification System
1. Köppen – German climatologist and botanist
2. first version 1918
3. basis for classification:
a. average annual and average monthly values of temperature and precipitation
b. 4 of 5 major climatic groups defined primarily by temperature characteristics
c. B group defined on basis of moisture
d. subdivided each group according to various temperature and precipitation relationships
4. modified Köppen System (Tables 8-1 and 8-2, Fig 8-3)
a. Köppen’s 5 major climatic groups (A through E)
b. subdivided into total of 14 individual climate types
c. 6th group: H – highland climates
D. Köppen Letter Code System
1. first letter designates the major climate group (A-E, H)
2. second letter describes precipitation patterns
3. third letter (if any) describes temperature patterns
E. Climographs
1. graphic representation of monthly temperature and precipitation for specific weather station
2. line graph for monthly temperature
3. bar graph for monthly precipitation
II. World Distribution of Major Climatic Types
A. Tropical Humid Climates (Zone A) (Table 8-3, Fig 8-5)
1. general characteristics
a. almost all land area within the tropics
b. climates of perpetual warmth; winterless climates
c. prevalence of moisture
1) much of A zone is among wettest in the world
2) onshore winds and thermal convection associated with the ITCZ are common and provide mechanism for uplift
d. 3 subtypes classified on basis of annual rainfall
1) tropical wet: abundant rainfall every month
2) tropical savanna: low-sun dry season and prominent but not extraordinary high-sun wet season
3) tropical monsoon: dry season and distinct very rainy high-sun wet season
2. Tropical Wet Climate (Af)
a. geographic location
1) astride the equator to 5o –10o poleward on each side
2) on east coasts may extend as far as 25oN/S
3) largest areas: upper Amazon basin, northern Congo basin, and islands of the East Indies
b. characteristics
1) monotonous, seasonless climate
2) every month has average temperature close to 80oF
3) average daily temperature range exceeds the average annual temperature range
a) smallest annual temperature range of any climate type
b) “Night is the winter of the tropics”
4) high humidity ® high sensible temperature
5) yearly rainfall (60-100+ inches) exceeded only by Am climates
a) rain can be expected every day
b) convective storms yield heavy rain for a short time
c. principal climatic control is latitude ® considerable thermal convection
1) trade wind convergence of ITCZ
2) onshore winds along trade-wind (east-facing) coasts
3) lack of wind except along coastlines
3. Tropical Savanna Climate (Aw)
a. geographic location
1) most extensive of A climates
2) lies north and south of Af climates
3) Africa, South America, and southern Asia
b. characteristics
1) clear cut seasonal alternation of wet and dry periods
2) between unstable, converging air on equatorial side and stable, anticyclonic air on poleward side
3) winds and pressure shift latitudinally with sun ® significant weather contrasts
a) in low sun/winter season subtropical high pressure dominates ® clear skies
b) in high sun/summer season ITCZ dominates ® wet tropical weather
4) typical annual precipitation: 35-70 inches
5) annual temperature range: 5o – 15oF
4. Tropical Monsoonal Climate (Am)
a. geographic location
1) most extensive: windward/west facing coasts of SE Asia (India, Myanmar, Thailand)
2) western Africa, northeastern South America, the Philippines, northeast Australia, East Indies
b. characteristics
1) receive enormous rainfall during high sun season/”summer” monsoon
a) 30 inches of rain in each of 2 or 3 months
b) annual total: 100-200 inches
c) Cherrapunji, India (annual average = 425”) - world record: 1,042” in 1 year
2) low sun season/”winter” monsoon: offshore winds dominate ® little precipitation
B. Dry Climates (Zone B) (Table 8-4, Fig 8-12)
1. general characteristics
a. cover 30% of world’s land area (more than any other climate zone)
1) largest expanses in subtropical latitudes
a) subsidence from subtropical high pressure cells suppresses upward vertical motion of air
b) cool ocean currents increase atmospheric stability
3) in the midlatitudes found in areas cut off from moisture sources
a) far from water bodies
b) in rainshadow of mountain ranges
c) central Eurasia
b. depends not only on precipitation but also on temperature
1) balance between precipitation and evapotranspiration
2) hot regions can receive more precipitation than cool regions and yet be classified as dry
c. two categories (generally):
1) desert: extremely arid
2) steppe: semi-arid
d. further classified based on temperature
1) subtropical = “hot”
2) midlatitude = “cold:
2. Subtropical Desert Climate (BWh)
a. geographical location
1) band near the subtropical highs in both Northern and Southern Hemispheres
2) extends to western coasts on all continents; not to eastern coasts
3) enormous expanse in North Africa (Sahara) and southwest Asia (Arabian Desert)
a) year-round anticyclonic conditions
b) remoteness from any moisture source
4) 50% of Australia, much in rainshadow of east coast mountains
5) Atacama Desert of South America
a) longest and driest desert in the world
b) double rainshadow
(1) Andes Mountains
(2) Peru/Humboldt: world’s coldest current
c) Arica, Chile: world record least annual average precipitation (0.03”/year) and longest rainless spell (14 years, 4 months)
b. characteristics of desert climates (BWh)
1) lack of moisture
a) scarce: annual totals 2-8 inches
b) unreliable: the less the average annual precipitation, the greater its variability – thus concept of “average” yearly rainfall in a BWh location is misleading
c) intense: rain that does fall comes as intense convective showers, localized and of short duration ® brief flooding
2) temperature
a) result of vertical sun rays and lack of cloudiness
b) moderate annual temperature range: 15o - 25oF
c) clear skies and low water vapor content permits rapid nocturnal cooling which results in astounding daily temperature range: 50oF in spring and fall
d) Dallol, Ethiopia: highest average daily maximum temperature (106oF) and highest annual average temperature (94oF)
e) El Azizia, Libya: highest recorded temperature (136oF)
f) In-Salah, Algeria: greatest 1 day temperature range (100oF)
3) windy days
4) western coasts in subtropical deserts
a) cold offshore currents
b) advective cooling: frequent fog
c) extremely low precipitation
3. Subtropical Steppe Climate (BSh)
a. surrounds the BWh except on western sides
b. extremes are more muted than desert climate
c. meager precipitation has seasonal concentration
4. Midlatitude Desert Climate (BWk)
a. geographical location in deep interiors of continents
1) conditions
a) far removed geographically from moisture source
b) mountain ranges block oceanic influence
2) significant regions:
a) central Eurasia
b) western North America
c) southern South America
b. characteristics
1) precipitation
a) meager and erratic
b) differences with BWh:
(1) bulk of precipitation comes in summer
(2) although most showery, some protracted drizzle
2) temperature differences with BWh
a) severely cold winters – average cold month temperature is normally below freezing
b) average annual temperatures much lower
c) greater annual temperature range: up to 54oF
5. Midlatitude Steppe Climate (BSk)
a. transitional between desert and humid climates
b. differences with BWk
1) more precipitation
2) less temperature extremes
c. extensive steppe climate in western North America
d. only in the interior southwest of the US is climate arid enough to be classified as desert
C. Mild Midlatitude Climates (Zone C) (Table 8-5, Fig 8-20)
1. general characteristics
a. marked seasonal contrasts
1) differences in temperature more prominent than in precipitation
2) clearly summer and winter (v. wet and dry in tropics)
3) summers long and hot
4) winters short and relatively mild
b. occasional frost means no year round growing season
c. precipitation is highly variable in terms of total amount and seasonal distribution
d. 3 categories
1) primary basis: precipitation seasonality
2) secondary: summer temperature
2. Mediterranean Climate (Csa, Csb)
a. geographical location
1) western sides of continents centered at latitudes 35o N and S
2) mostly small regions restricted to coastal areas either by interior mountains or by limited landmasses
3) regions:
a) borderlands of Mediterranean Sea (only extensive area)
b) central and southern California
c) central Chile
d) southern tip of Africa
e) southwestern corners of Australia
b. characteristics
1) modest precipitation falls in winter; summers virtually rainless (marine west coast climate only other one with winter precipitation concentration)
2) mild winter temperatures
3) abundant clear skies and sunshine, especially in summer
c. Csa: hot summers w/monthly average temperature 75oF - 85oF
d. Csb
1) coastal areas
2) milder summers and winters
3) frequent coastal advection fog
e. climate explanation
1) dry, stable, subsiding air from subtropical high dominates in summer
2) westerlies dominate in winter
3. Humid Subtropical Climate (Cfa, Cwa)
a. geographical location
1) eastern side of continents at same latitude as Mediterranean climates but more extensive both latitudinally and longitudinally
2) extends from 15oN/S to 40oN/S
3) greatest east-west extent: North America, Asia, South America
b. differences with mediterranean climates:
1) summers are warm to hot
a) higher humidity ® higher sensible temperatures
b) little nighttime relief
2) summer precipitation maximum
a) result of onshore flow and frequent convection
b) annual precipitation: 40” – 60”
3) winter temperatures mild on average but cold waves
a) minimum winter temperatures: 10o to 20oF colder than Mediterranean climates ® killing frosts
b) agricultural adjustments:
(1) northern limit citrus production in eastern US (Florida-Cfa): 29oN
(2) northern limit citrus production in western US (California-Cs): 38oN
4. Marine West Coast Climate (Cfb, Cfc)
a. geographical location
1) western side of continents
2) latitudinal range: 40o – 60oN/S
3) windward location – westerlies at this latitude
4) regions:
a) extensive in western and central Europe
b) northwestern US: limited interiorward by mountain ranges
b. characteristics
1) persistent onshore air movement ® extraordinarily temperate climate considering the latitude
2) lack of extreme temperatures
3) consistently high humidity
4) high cloudiness, many days w/precipitation
c. temperature
1) moderated most of the time by oceanic influence
2) frosts are relatively infrequent
3) abnormally long growing season for this latitude
4) 1 month longer growing season in Seattle than Atlanta (which is 14o farther south!)
d. precipitation
1) among the wettest climates of the midlatitudes, although total amount of precipitation in not remarkable except in upland areas
2) average annual precipitation: 30-50”; higher on exposed mountain slopes
3) snow uncommon in lowlands, but higher, west facing slopes receive some of heaviest snowfalls in the world
4) precipitation frequency marks these climates
a) rainfall probability and reliability are high
b) intensity is low: drizzly frontal precipitation
c) Seattle receives 43% of possible sunshine v. Los Angeles 70%
D. Severe Midlatitude Climates (Zone D) (Table 8-6, Fig 8-27)
1. characteristics
a. occur in northern hemisphere only
1) latitudinal range: 40o – 70oN
2) limited land mass in southern hemisphere
b. continentality: remoteness from oceans
1) dominates D climates
2) ® extremely large annual temperature ranges
c. 4 seasons
d. moderate precipitation
1) exceeds potential evapotranspiration
2) summer precipitation maximum
e. 2 types based on temperature
1) humid continental: long, warm summers
2) subarctic: short summers, very cold winters
2. Humid Continental Climate (Dfa, Dfb, Dwa, Dwb)
a. geographic location
1) North America and Asia: 35o – 55oN
2) Europe: 35o – 60oN
b. characteristics
1) westerly winds dominate ® migratory pressure systems ® great weather variability and dramatic changes
2) warm summers: average mid 70so F
3) winters: 1-5 months average below freezing
4) precipitation: 20-40 inches
a) decreases from coast to interior
b) decreases from south to north
3. Subarctic Climate (Dfc, Dfd, Dwc, Dwd)
a. geographic location
1) 50o – 70o N
2) 2 vast uninterrupted expanses:
a) from western Alaska across Canada
b) Eurasia, from Scandinavia to easternmost Siberia
3) boreal – refers to Canadian climatic type
4) taiga – refers to Eurasian climatic type
b. characteristics
1) winter: long, dark, bitterly cold
a) 6-7 months average temperature < freezing
b) world’s coldest temperature records (other than ice caps)
(1) Siberia: - 90oF
(2) Alaska: - 82oF
2) long summer days ® warm
3) largest annual temperature ranges in the world
a) > 80oF
b) world record absolute annual temperature variation: Verkhoyansk, Siberia 188o F (-90o to +98o F)
c) world record greatest average annual temperature range: 112o F Yakutsk, Siberia (Dfd climate)
4) meager precipitation
a) annual averages 5 – 20”
b) low evaporation and frozen soil much of year ® moisture adequate to support forests
c) light snowfall but stays on ground Oct-May
E. Polar Climate (Zone E) (Table 8-7, Fig 8-32)
1. characteristics
a. enduring cold; too little insolation for any significant warming
b. all months average temperature ≤ 50oF
c. extraordinarily dry – but evaporation so low that qualifies as nonarid
d. 2 subcategories distinguished by summer temperature
1) tundra: at least 1 month with average temperature > freezing
2) ice cap: all months average temperature < freezing