Applied Climatology - World Climatic Classification

Three broad approaches

• Empirical - Based on observed data, articularly on temperature and precipitation.
• Genetic - Attempts to organise climates according to their causes.
• Applied - Classification is for specific purpose.

Koeppen’s Scheme of Classification of Climate

• Koeppen identified a close relationship between the distribution of vegetation and climate – Developed in 1918.
• Empirical classification based on mean annual and mean monthly temperature and precipitation data.
• The capital letters: A, C, D and E delineate humid climates and B dry climates.
• A (Tropical) - Average temperature of the coldest month is 18° C or higher.
• B (Dry Climates) - Potential evaporation exceeds precipitation.
• C (Warm Temperate) - The average temperature of the coldest month of the (Mid-latitude) climates years is higher than minus 3°C but below 18°C.
• D (Cold Snow Forest Climates) - The average temperature of the coldest month is minus 3° C or below.
• E (Cold Climates) - Average temperature for all months is below 10° C.
• H (High Land) - Cold due to elevation
• The Small letters: f, m, w and s. Where, f corresponds to no dry season, m - monsoon climate, w- winter dry season and s - summer dry season. The small letters a, b, c and d refer to the degree of severity of temperature.

Group	Type	Letter  Code	Charactertstics
A-Tropical Humid Climate	Tropical wet Tropical monsoon Tropical wet and dry	Af Am Aw	No dry season Monsoonal, short dry season Winter dry season
B-Dry Climate	Subtropical steppe Subtropical desert Mid-latitude steppe Mid-latitude desert	BSh BWh BSk BWk	Low-latitude semi-arid or dry Low-latitude arid or dry Mid-latitude semi-arid or dry Mid-latitude arid or dry
C-Warm temperate (Mid latitude) Climates	Humid subtropical Mediterranean Marine west coast	Cfa Cs Cfb	No dry season, warm summer Dry hot summer No dry season, warm and cool summer
D-Cold Snow forest Climates	Humid continental Subarctic	Df Dw	No dry season, severe winter Winter dry and very severe
E-Cold Climates	Tundra Polar ice cap	ET EF	No true summer Perennial ice
H-Highland	Highland	H	Highland with snow cover

Group A: Tropical Humid Climates

• Exist between Tropic of Cancer and Tropic of Capricorn.
• Sun being overhead throughout the year and the presence of Inter Tropical Convergence Zone (ITCZ) make climate hot & humid.
• Annual range of temperature is very low and annual rainfall is high.
• Rainfall: Am < Aw < Af.
1. Tropical Wet Climate (Af)
• Found near the equator (Amazon Basin in South America, western equatorial Africa & islands of East Indies).
• Rainfall every month, thunder showers in the afternoon.
• Temperature, Maximum: 30^o C & Minimum: 20^o C.
• Dense canopy cover and large biodiversity.
2. Tropical Monsoon Climate (Am).
• Indian sub-continent, North Eastern part of South America and Northern Australia.
• Mostly Heavy rain in Summer, Winter is Dry.
3. Tropical Wet and Dry Climate (Aw).
• North and south of Af type climate regions.
• Borders with dry climate on the western part and Cf or Cw on the eastern part.
• North and south of the Amazon forest, adjoining parts of Bolivia and Paraguay in South America, Sudan and south of Central Africa.
• Wet is Shorter & Dry is Longer with drought.
• Temperature high throughout the year. Deciduous forest and tree-shredded grasslands.

Group B: Dry Climates

• Very low rainfall that is not adequate for the growth of plants.
• Latitude: 15 ^o - 60 ^o N & S of Equator.
• Low Latitude: 15 ^{o -} 30 ^o N & S of Equator (Sub tropical High) - Inversion of temperature do not produce rainfall.
• Middle Latitude: 35 ^{o –} 60 ^o N & S of Equator - maritime-humid winds do not reach and to areas often surrounded by mountains.
1. Semi-arid climate (BS) and desert climate (BW)
• 15° - 35° - Subtropical steppe (BSh) and subtropical desert (BWh).
• 35° - 60° - Mid-latitude steppe (BSk) and mid-latitude desert (BWk).
2. Subtropical Steppe (BSh) and Subtropical Desert (BWh) Climates.
• Common precipitation and temperature (annual & diurnal range is high).
• Subtropical steppe receives slightly more rainfall than the desert, adequate enough for the growth of sparse grasslands.
• Variability in the rainfall affects the life in the steppe much more than in the desert.
• Fog is common in coastal dessert.
• Highest shade temperature of 58° C at Al Aziziyah.

Group C: Warm Temperate (Mid-Latitude) Climates.

• 30° - 50° of latitude mainly on the eastern and western margins of continents.
1. Humid Subtropical Climate (Cwa)
• Dry in winter & Hot in Summer.
• Poleward of Tropic of Cancer and Capricorn (North Indian plain & South China interior plains).
• Similar to Aw climate except that the temperature in winter is warm.
2. Mediterranean Climate (Cs)
• Around Mediterranean see, between 30° - 40° latitudes (Central California, Central Chile, along the coast in south eastern and south western Australia).
• Sub-tropical high in summer and westerly wind in winter. Precipitation 35 – 90 cm.
• Hot, dry summer (25° C) and mild, rainy winter (10°C).
3. Humid Subtropical (Cfa) Climate
• Eastern parts of the continent in subtropical latitudes.
• Unstable and cause rainfall (75 – 150 cm) throughout the year.
• Eastern United States of America, southern and eastern China, southern Japan, northeastern Argentina, coastal south Africa and eastern coast of Australia.
• Thunderstorms in summer (27° C) and frontal precipitation in winter (5° - 12° C).
4. Marine West Coast Climate (Cfb)
• Poleward from the Mediterranean climate on the west coast of the continents.
• Northwestern Europe, west coast of North America, north of California, southern Chile, southeastern Australia and New Zealand.
• Temperature is moderate and in winter, it is warmer than for its latitude.
• Summer: 15° - 20° C & Winter: 4° - 10° C. Precipitation: 50 – 250 cm.

Group D: Cold Snow Forest Climates

• Between 40° - 70° North latitude in Europe, Asia & Africa.
1. Cold Climate with Humid Winters (Df)
• Poleward of marine west coast climate and mid latitude steppe. Cold & Snowy.
• Weather changes are abrupt and short.
2. Cold Climate with Dry Winters (Dw)
• Northeastern Asia. development of pronounced winter anti cyclone and its weakening in summer sets in monsoon like reversal of wind in this region.
• Summer temperatures are lower and winter temperatures are extremely low. Freezing point upto eight months.
• Precipitation is low from 12-15 cm.

Group E: Polar Climates

• Exist poleward beyond 70° latitudes.
1. Tundra Climate (ET)
• Low growing mosses, lichens and flowering plants.
• Sub soil is permanently frozen.
• Summer, long duration of day light.
2. Ice Cap Climate (EF)
• Interior Greenland and Antartica.
• Summer, Temperature below freezing point.
• Deformation of the ice sheets and they break.
• Plateau Station, Antarctica ,79°S, portray this climate.

Group H: Highland Climates

• Governed by topography. High mountains, large changes in mean temperature occur over short distances.
• Precipitation vary & Vertical zonation of layering of Climate types.

Climate Change

• Type of climate we experience now might be prevailing over the last 10,000 years with minor and occasionally wide fluctuations.
• Geological records show alteration of glacial and inter-glacial periods.
• High altitudes and high latitudes, exhibit traces of advances and retreats of glaciers.
• Sediment deposits in glacial lakes also reveal the occurrence of warm and cold periods.
• Rings in the trees provide clues about wet and dry periods.
• Rajasthan desert, wet and cool climate - 8,000 B.C. The period 3,000- 1,700 B.C. - higher rainfall. From 2,000-1,700 B.C. - centre of the Harappan civilisation.
• Present inter-glacial period started 10,000 years ago.

Climate in the recent past

• 1990s - warmest temperature of the century.
• worst devastating drought in the Sahel region, south of the Sahara Desert, from 1967-1977.
• Dust bowl - drought occurred in southwestern Great Plains of the United States.
• Warm and dry conditions in the tenth and eleventh centuries.
• “Little Ice Age” from 1550 to about 1850.
• 1885-1940, world temperature upward trend. After 1940, the rate of increase in temperature slowed down.

Causes of Climate Change

• Astronomical (associate with sunspot activities) - sunspots increase, cooler and wetter weather and greater storminess occur. sunspots decrease, warm & drier condition.
• Millankovitch oscillations - Variations in the earth’s orbital (Axial tilt) characteristics around the sun. – alter insolation.
• Volcanism – Volcanic eruption, aerosols in atmosphere reduce sun radiation reach earth.
• anthropogenic effect - Increasing trend in the concentration of greenhouse gases.
• Terrestrial causes.

Global Warming

• The gases that absorb long wave radiation are called greenhouse gases.
• The processes that warm the atmosphere are often collectively referred to as the greenhouse effect.

Greenhouse Gases (GHGs)

• CO₂ (largest Concentration), CFCs (Highly effective – destroy Ozone), CH₄, N₂O, O₃ & CO react with GHGs & affect atmosphere.
• Kyoto protocol proclaimed in 1997. This protocol went into effect in 2005, ratified by 141 nations.35 industrialised countries to reduce their emissions by the year 2012 to 5 per cent less than the levels prevalent in the year 1990.
• Cause: Rise in the sea level due to melting of glaciers and ice-caps and thermal expansion of the sea.
• 1901-44 and 1977-99 – Global temperature rose to 0.4C. globally averaged annual mean temperature at the end of the 20th century was about 0.6C above that recorded at the end of the 19th century.