◄UNIT 4 SOILSUNIT 6 NATURAL VEGETATION OF THE WORLD►

UNIT 5 WEATHER AND CLIMATE IN THE WORLD

  • UNIT 5 WEATHER AND CLIMATE IN THE WORLD

    Key Unit competence: The student-teacher should be able to appreciate
    the importance of the atmosphere, weather and the
    impact of climate on the environment and human

    activities in the world.

    5.1.1. Definition of atmosphere, weather and climate

    i. Atmosphere
    The atmosphere is a mixture of gases surrounding the earth and retained by
    the force of the earth’s gravity. It is an envelope of gases surrounding the earth.
    It contains the gases that support all forms of life on earth. This envelope of air
    is dense at the sea level. It thins out with increase in altitude.

    ii. Weather
    Weather can be defined as the state of the atmosphere at any given time. This
    state is about temperature, atmospheric pressure, wind speed and direction,
    moisture, cloud cover, precipitation, and sunshine. Weather keeps changing all
    the time. The change is from hour to hour and day to day.

    Weather is also defined as the condition of the atmosphere at a particular place
    over a short period. Weather changes from time to time. The weather can be
    windy, cloudy, sunny, hot etc. Elements of weather include temperature, rainfall,
    humidity, air pressure, sunshine, winds and cloud cover. Weather involves the
    behavior of all above elements at a place and a particular time.

    Weather is measured from a weather station. A weather station is a place
    where the elements of weather are measured and recorded. Some of weather
    recording instruments like thermometers are kept in a Stevenson screen, which
    is special double boarded, louvered and wooden box in which thermometers,
    are hung at weather station. Steven screen is designed in special way as follow:

    • It is painted white to reflect heat,
    • It is placed on stands about 120 cm above the ground. This is to ensure
    that air pressure is measured or to tap freely the moving wind,
    • It has louvers (wooden) to protect the thermometers from direct sun
    rays and allow free circulation of air,
    • It is made of wood because wood is a poor conductor of heat,
    • The roof is double boarded to prevent the sun’s heat from reaching
    inside the screen,
    • It is placed away from buildings or tree shades,
    • The screen is also placed on grass covered surface to minimise radiation

    from the earth’s surface.

    Weather recording instruments include:


    III. Climate

    Climate is an average weather conditions of a place measured, recorded,
    studied and analyzed over a long period of time 30-35 years. It is measured
    by assessing the patterns of variation in temperature, humidity, atmospheric
    pressure, precipitations, wind speed and direction.

    The elements of weather and climate: Weather and climate are made
    up of many elements. The main ones are temperature, precipitation, wind,
    atmospheric humidity, clouds, sunshine and atmospheric pressure.

    5.1.2 The structure of the atmosphere
    The atmosphere is a mixture of various gases surrounding the earth. It
    provides all gases that are essential for sustaining all life forms on the earth.
    Based on temperature variation, the atmosphere is made up of four layers: the

    troposphere, the stratosphere, the mesosphere and the thermosphere.


    The structure of the Atmosphere

    i. Troposphere
    This is the lowest layer of atmosphere, extending from the earth’s surface to a
    height of about 8 km at the poles and 18 km at the equator. Temperature, within
    this layer, generally falls by 0.650 per 100m of ascent with increasing altitude
    up to the upper limit, the tropopause. The troposphere is the most important
    because all the elements of weather and weather phenomena occur in this
    layer (e.g. evaporation, condensation, and precipitation of different forms like
    fog, cloud, dew, frost, rainfall, snowfall, thunder, lightning, atmosphere storms,
    etc.). This layer contains about 75% of gaseous mass of the atmosphere, most
    of water vapour, aerosols and pollutants.

    Briefly, troposphere is characterized by the following:
    • It is the lowest layer of the atmosphere.
    • The upper limit of the troposphere is called the tropopause.
    • The temperature decreases with altitude at the rate of 6.5°C per 1km/
    1000m
    • The atmospheric pressure decreases also with altitude and reaches to
    100 millibars and 250 millibars over the equator and poles respectively
    at tropopause.
    • It lies between 10 km and 20 km above the sea level.
    • All weather phenomena occur in this layer. These are evaporation,
    condensation and precipitation. Condensation is the conversion of
    vapour or gas into a liquid of different forms. Precipitation is water
    that falls to the ground as rainfall, snow or hail.
    • The height of tropopause is 17 km over Equator and 9 to 10 km over
    the poles.
    • The higher one goes, the cooler it becomes. The decrease in temperature
    with height is called the environmental Lapse rate.
    • The reasons why temperature decreases in troposphere with height:
    • Effect of terrestrial radiation: The earth emits back parts of the solar
    radiation into the atmosphere. The radiation definitely reduces as the
    distance away from the ground increases.

    • The effect of adiabatic compression: The atmospheric pressure
    is highest on the surface and reduces away from the surface. The
    atmospheric pressure compresses air molecules and increases
    molecular activity. The air molecules in high pressure surface regions

    give high temperature than the areas high in atmosphere.

    The role of man activities: Industrialization, bush burning, the use of
    automobiles increase temperature on the earth.
    • Solid nature of the earth stores more heat than the atmosphere
    • Abundance of water vapor in the atmosphere which absorb heat
    than high troposphere.

    ii. Stratosphere:
    The stratosphere is the layer which is extending from 16 to 50 km above the
    sea level.
    It is characterized by the following:
    • There is increase of temperature due to absorption of ultraviolet solar
    radiation by ozone layer and lesser density of air and the presence of
    many solid components (dust, smoke, ash, salt) which act as obstacles
    to solar radiation.

    • There is nearly absence of weather phenomena because of dry air and
    rare occurrence of clouds.
    • The lower portion of the stratosphere having maximum concentration
    of ozone is called ozonosphere, which is confined between the heights
    of 15 to 35 km from sea level. Depletion of ozone would result in the
    rise of temperature of the ground surface and lower atmosphere.
    The main causes of ozone destruction are halogenated gases called
    chlorofluorocarbons (CFCs: chlorine, fluorine and carbon). Ozone layer
    depletion results to global warming, acid rain, melting of continental
    glaciers and rise in sea level, skin cancer, poisonous smoke, decrease in
    photosynthesis, ecological disaster and ecosystem instability.
    • The upper limit of the stratosphere is known as stratopause.

    iii. Mesosphere
    • The mesosphere extends between 50 km and 80 km.
    • Temperature decreases as height increases. In fact, the rise of
    temperature with increasing height in the stratosphere stops at the
    stratopause.

    • The temperature decreases in altitude because this layer is almost
    empty of components which would capture solar radiation.
    • At the uppermost limit of the mesosphere (80 km), the temperature
    drops at -80° C and may go down as low as - 100° C to -133° Celsius at

    mesopause.

    • This layer is characterized by very low air pressure ranging between
    1.0 millibar at 50 km altitude representing stratopause, and 0.01
    millibars at the mesopause (between 90 and 100 km).

    iv. Thermosphere
    It extends from 80 km to 640 km. It is composed of Ionosphere and Exosphere.
    a. The ionosphere consists of the following ionized layers:
    • D layer: reflects low-frequency radio waves but absorbs medium and
    high-frequency waves. Being closely associated with solar radiation, it
    disappears as soon as the sun sets.
    • E layer: The E-layer is also called the Kennelly-Heaviside layer. It
    reflects the medium and high-frequency radio waves. It is much better
    defined than the D layer. It is produced by ultraviolet photons from the
    sun rays interacting with nitrogen molecular. This layer also does not
    exist at night.
    • Sporadic E-layer: This layer occurs under special circumstances. It
    is believed that this sporadic layer is caused by meteors and by the
    same processes that cause aurora lights. This layer reflects very high
    frequency radio waves.
    • E2 layer is generally found at the height of 150 km and is produced due
    to the reaction of ultra-violet solar photons with oxygen molecules.
    This layer also disappears during the night times.
    • F layer consists of two sub-layers e.g. F1 and F2 layers (150 km-380
    km) are collectively called the Appleton layer. These layers reflect
    medium and high frequency radio waves back to the earth.
    • G layer (400 km and above) most probably persists day and night but
    is not detectable.

    b. The exosphere represents the uppermost layer of the atmosphere.
    The density becomes extremely low. The temperature reaches 5568° C
    at its outer limit, but this temperature is entirely different from the air
    temperature of the earth’s surface as it is never felt. The atmosphere
    above the ionosphere is called the outer atmosphere and it is made of

    exosphere and the magnetosphere.

    5.2.1. Composition of atmosphere
    Basically, the atmosphere is composed of three major constituents, namely:
    gases, water vapour, and aerosols. These constituents of the atmosphere
    are either permanent (Nitrogen Oxygen, Argon, Carbon dioxide, hydrogen,
    neon, Helium, Krypton, ozone and Xenon) or temporary constituents include
    solid (dust, smoke, salt and volcanic ash), liquid (water vapour) and gaseous.
    i. Gases

    The main gases are shown in the table below:



    The following are the most important components of the atmosphere:

    1. Nitrogen, which is about 78.1% of the total gases. Nitrogen is for all life
    forms. It is an important part of amino acids which make up proteins.
    Nitrogen (N) is one of the building blocks of life: it is essential for all
    plants and animals to survive. Nitrogen (N2) makes up almost 78.1%
    of our atmosphere. Humans and most other species on earth require
    nitrogen in a “fixed,” reactive form.

    Life depends on nitrogen, which is a basic ingredient in amino acids that
    make up all proteins. While a substantial percentage of the atmosphere
    is comprised of nitrogen gas, it must be processed into a soluble form.
    This is done via a nitrogen cycle that occurs in the soil. Then plants and
    the animals that eat them can obtain dietary nitrogen.

    Plants with nitrogen deficiencies look weak. Their leaves, which should
    be healthy and green, may look wilted and yellow. Animals and people
    get dietary nitrogen by eating protein-rich foods like milk, eggs, fish, beef
    and legumes. Nitrogen, carbon, hydrogen and oxygen are found in amino
    acids, which are the main structures of every protein.

    The nitrogen cycle involves:
    • Transfer of atmospheric nitrogen into soils (known as nitrogen
    fixation);
    • Mineralization, nitrification and transfer of nitrogen from soils to
    plants.
    • Denitrification and return of nitrogen to the atmosphere. It helps the
    oxygen in combustion; it also helps indirectly in oxidation of some
    elements.

    2. Oxygen: This makes up 20.9% of gases in the atmosphere. The molecular
    oxygen (O2) mostly occurs up to the height of 60 km in the lower
    atmosphere. It is produced through photosynthesis. This is the process
    by which green plants use sunlight, carbon dioxide and water to make
    their own food. It is one of the main elements that make up air, and it is
    necessary for the survival of all plants and animals e.g. animals breathe
    in oxygen.

    3. Carbon dioxide represents 0.03% of the total atmospheric gases. The
    gaseous carbon (CO2) plays two significant roles:
    • Carbon dioxide helps in the process of photosynthesis where carbon,
    hydrogen, and oxygen are combined by the autotrophic green plants
    of terrestrial and marine ecosystem. This is assisted by sunlight that
    enables the formation of the organic compounds.

    • Carbon dioxide is transparent to incoming shortwave solar radiation. It
    is opaque to outgoing long wave terrestrial radiation. It is evident that
    carbon dioxide is most significant greenhouse gas. The concentration
    carbon dioxide increases due to the anthropogenic activities, namely
    the burning of fossil fuels and wood and deforestation which lead to
    probable climate change through global warming.

    4. Ozone (O3): It is defined as “a three-atom isotope of oxygen (O3) or
    merely a triatomic form of oxygen (O3). It is formed with the separation
    of (O2). Then, these separated oxygen atoms (O) are combined with
    Oxygen molecules (O2) and thus ozone (O3) is formed. It is a life-saving
    gas because it filters the incoming shortwave solar radiation and absorbs
    ultraviolet rays. Therefore, the ozone layer protects the earth from
    becoming too hot. It is known as the earth’s umbrella to all organisms
    in the biospheric ecosystem against their exposure to ultraviolet solar
    radiation. The highest concentration of ozone is between the altitudes of
    12 km and 35km in stratosphere; the said zone is also called ozonosphere.

    5. Water vapour: Liquid water turns into vapour through the process
    of evaporation. The content of water vapour decreases with the
    altitude in the atmosphere. More than 90% of the water vapour in the
    atmosphere is found up to a height of 5 km. The moisture content in the
    atmosphere creates clouds, fogs, rainfall, frost, snowfall and other forms
    of precipitation.

    6. Aerosols: These are suspended solid particles and liquid droplets. These
    particles are from various sources like volcanic eruptions, desert dust,
    spores and pollen. The concentration of these particles decreases with

    increasing altitude in the atmosphere.

    5.2.2. Importance of the atmosphere
    The atmosphere is important for the following reasons:

    • It protects living things from harmful ultraviolet rays of the sun. This
    role is played by the ozone layer.

    • The atmosphere protects the earth from receiving too much radiation
    from the sun and reduces its harmful effects.

    • It helps to regulate the heat during the day and night. On earth,
    however, molecules in the atmosphere absorb the sun’s energy as it
    arrives, spreading that warmth across the planet. The molecules also
    trap reflected energy from the surface, preventing the night side of the
    planet from becoming too cold.

    • The Earth’s atmosphere protects and sustains the planet’s inhabitants
    by providing warmth and absorbing harmful solar rays.
    • The atmosphere traps the sun’s energy and sends off many of the
    dangers of space.
    • It provides the various gases that are useful to living things. These
    include oxygen.
    • It provides precipitation that helps to sustain life on earth.
    • The atmosphere is made of gases that are essential for photosynthesis
    and respiration, among other life activities.
    • The atmosphere is a crucial part of the water cycle. It is an important
    reservoir for water and the source of precipitation.
    • The atmosphere moderates Earth’s temperature because greenhouse
    gases absorb heat.
    • Atmosphere contains the oxygen and carbon dioxide, which living
    things need to survive.

    • The atmosphere also serves an important purpose as a medium for
    the movement of water. Vapour evaporates out of oceans, condenses
    as it cools and falls as rain. Hence, providing life-giving moisture to
    otherwise dry areas of the continents. Without an atmosphere, it
    would simply boil away into space, or remain frozen in pockets below
    the surface of the planet.

    • The atmosphere separates the earth from the space and thus, hot

    meteors do not hit the ground all the time.

    Climates are classified according to the average and the typical ranges of
    different variables, most commonly temperature and precipitation. There are
    three world climatic zones. These are: Tropical, Temperate and Cold zones.

    5.3.1. Tropical zones
    5.3.1.1 Equatorial climate.
    Equatorial climate is also called tropical wet climate or tropical rainforest
    climate. It is found along the equator extending from 5° to 10° South and North
    latitudes. Along the Eastern margin of continents, it spreads to 15° - 25° of
    latitudes. This type of climate is found specifically in the following regions:

    • The Amazon River Basin in South America
    • The Congo Basin and Guinea coast in Africa
    • Malaysia, Indonesia and the Philippines Islands in South-Eastern Asia
    • Eastern and Central America (parts of Panama, Costa Rica, Nicaragua,
    Honduras, British Honduras and Guatemala), some islands in the
    Western Colombia
    • Coastal lowlands of Eastern Brazil

    • Eastern Madagascar.

    Climatic characteristics of equatorial region

    • This climatic region is located within 5° North to 10° South of the
    Equator.
    • The average monthly temperatures are over 18°c. However, many
    places record average monthly temperatures of 24° to 27°c.
    • The Equatorial regions lie in a belt where the winds are light. It is a
    low-pressure belt.
    • The annual range of temperature is very small (the difference between
    the highest and the lowest temperatures) varies from 5°to 8°c.
    • The equatorial regions get heavy precipitation throughout the year.
    Many areas receive 2000 mm of the rain per year. The annual average
    rainfall in the equatorial climate is nearly 2500 mm.
    • There is a large amount of cloudiness.
    • Conventional rainfall is received, and it is usually accompanied by
    thunderstorms.
    • High temperatures and heavy rainfall encourage growth of natural
    vegetation. There are evergreen dense forests.

    Below there is an example of Singapore weather station:

    Singapore weather station


    5.3.1.2 Tropical marine climate
    It is found on the East coasts of regions lying between 10° N and 25° N and
    10° S and 25° S of the equator. These areas come under the influence of onshore
    Trade Winds. Examples are East coast of Brazil, the Eastern coastlands of
    Madagascar, Mexico, Nicaragua, Guatemala, Venezuela, the lowlands of Central
    America, West Indies, the coast of Queensland (Australia) and the southern

    islands of the Philippines.

    Climatic characteristics of Tropical maritime/maritime climate
    • The annual temperature range is about 8°c.
    • Temperatures reach 29°c during the hot season while it is about 21°c
    during the cold season,
    • Annual rainfall varies from 1000 mm to 2000 mm.
    • Rainfall received is both convection and orographic brought by onshore
    Trade Winds.
    • Humidity is high throughout the year.
    • Sea breezes lessen the effects of the heat.
    • Tropical maritime climate is good for tree growth. The lowlands have

    tall and evergreen trees.

    Cameroon weather station


    5.3.1.3 Tropical continental climate
    This climate occurs between 5° N and 15° N and 5° S and 15° S. It is in West,
    East and Central Africa, South America, parts of the Deccan plateau (India) and

    the areas to the north and east of the Australian Desert.


    Tropical continental climate
    Climatic characteristics of Tropical continental climate
    • Heavy convectional rainfall is mainly in the summer.
    • Annual rainfall is about 765 mm.
    • In some regions, the offshore winds are strong and hot. An example is
    the Harmattan of West Africa.
    • Humidity is high during the hot, wet season.
    • Summers are hot (32° C) and winters are cool (21° C).
    • The annual temperature range is about 11°C. The highest temperatures
    occur just before the rainy season begins. This is in April in the northern
    hemisphere and October in the southern hemisphere.

    5.3.1.4 Savannah climate (Tropical wet-and-dry climate
    This is located between 5° and 20° latitudes on either side of the Equator. It is
    found in Latin America. These are the Llanos of the Orinoco Valley including

    Colombia and Venezuela, the Guyana Highlands and the Campos of Brazil.

    In Africa, it is found in the South of the Congo basin, the Southern part of
    Democratic of Republic of Congo, Angola, Zambia, Mozambique, Tanzania,
    Uganda, Botswana, South-Western Madagascar, Central Nigeria, Southern

    Kenya, Togo, Ghana and Ivory Coast.

    Savannah Tropical climate

    Climatic characteristics of Savannah Tropical climate
    • High temperature of around 20°c.
    • The annual range of temperature is greater than in the equatorial
    regions. It is over 3° but not more than 8°c.
    • Total annual average precipitation varies from 1000 mm to 1500 mm.
    Much of the rain falls during the summer.
    • The vegetation is grasslands with scattered trees and bushes.

    5.3.1.5 Tropical desert climate
    Most of these deserts lie between 15° to 35° N and S. The hot desert climate is
    found in the following deserts: Atacama (the coastal deserts of Peru and Chile
    in South America), the Namib and Kalahari deserts of coastal Angola and South
    West Africa, interior part of Botswana and South Africa, the great Australian
    desert, the Sahara and the Arabian deserts, the Iranian desert, the Thar desert

    of Pakistan and India, California (USA) and the deserts of Northern Mexico.


    Tropical desert climate
    Characteristics of Tropical desert climate
    • Hot deserts have the highest temperatures recorded.
    • They have cloudless skies and little or no water vapour.
    • The daily ranges of temperature vary between 22° to 28° C. In rare
    cases, the diurnal range may be as high as 41.7° C.
    • The annual average precipitation is less than 250 mm.
    • Relative humidity is high.
    • There is little plant cover.

    Below is an example of Khartoum (Sudan) weather station:


    5.3.1.6 Tropical Monsoon Climate

    This is found in areas with seasonal land and sea winds. On-shore summer winds
    blowing from over tropical warm Oceans bring about heavy precipitation. Offshore
    winds from over the land make the weather dry during winter.
    Monsoon climate is found in the coastal areas of Eastern and Southern Asia.
    These places include India, Burma, Bangladesh, Indo-china, Southern China,
    and Philippines, Taiwan, Japan and Korea.

    In tropical Africa, it is found along the South-West coast of West Africa. These
    areas include the coasts of Guinea, Sierra Leone, Liberia, and Ivory Coast.
    Other areas are the Northeast coast of Latin America from the mouth of Orinoco
    River in Eastern Venezuela through Guyana, Surinam and French Guyana to the
    North-Eastern part of Brazil. The North coasts of Puerto Rico and the Dominican

    Republic in the Caribbean Islands which have a mild monsoon climate.


    Tropical monsoon climate
    Characteristics of Tropical monsoon climate
    • High temperatures (32°c) in the hot season (summer) and low
    temperatures (15°c) in the cold season (winter).
    • High annual range of temperatures of about 17°c.
    • Summers receive high rainfall of up to 2500 mm.
    • The winters are dry.
    • There is a reversal of winds. In one season they blow from sea to land
    (onshore). These bring heavy rainfall. In the other season, they blow

    away from the sea (offshore), such come along with little rain.

    5.3.2 Temperate zone
    5.3.2 1 Mediterranean Climate
    Mediterranean climate is found between 30°and 40°N and S of the equator. This
    is on the western sides of the continents. This climate is found in five regions of
    the world:

    • North of the Mediterranean Sea from Portugal to Turkey and beyond
    in the Iranian Highlands, Morocco, Northern Algeria, and Tunisia, and
    North of Bengasi in Libya.
    • The central and Southern California coast in the United States of America.
    • Central Chile.
    • The Cape Town area of South Africa, and

    • Southern Western coasts of Australia.

    Mediterranean climate.
    Characteristics of Mediterranean climate

    • The average temperature of the coldest month is between 4.4°C and
    10°c. That of the hottest month is between 21° C and 27°c.
    • The mean annual temperature ranges are between 11°and 17°c.
    • The average annual precipitation is between 350 and 750 mm.
    • There is rain in winter while the summers are dry.
    Below there is an example of Algiers (Algeria) weather station:

    Algiers (Algeria) weather station

    5.3.2 2 Temperate Maritime Climate
    This type of climate is found between 40° and 65° N and S of the equator. These
    are regions to the West of continents.

    It is mainly found in Western Europe including Great Britain, North Western
    France, Germany, Denmark, Holland, Belgium and Norway.

    In North America, it is found along the West coast up to 60° N of the equator.
    It borders the Sub-Arctic climate of Canada and Alaska. In Europe, it extends
    along the west coast of Norway to 68° N.

    In the Southern Hemisphere, it is found to the Southwest coast of Chile,
    Southeast coast of Australia, the islands of Tasmania and New Zealand.

    Below there is an example of Brest (France) weather station:

    Brest (France) weather station



    Temperate maritime climate
    Characteristics of Temperate Maritime climate
    • Temperatures are influenced by the warm Ocean currents.
    • This climate has cool summers and mild winters.
    • The annual range of temperature is about 7° C.
    • Average temperatures in summer are between 15° C and 18° C. Winter
    temperatures range between 11° and 17° C.
    • In Europe, the lowlands receive an average precipitation of 500 mm to
    850 mm. On the windward side, it is between 2500 mm and 3750 mm.

    5.3.2.3 Continental Temperate climate
    This type of climate occupies a large part of the United States of America. In
    Europe, it is found in Romania and Bulgaria. It occupies the lower Danube Valley.

    In Eastern Asia, it is found in North China bordering the yellow Sea, North and

    South Korea, and Northern Honshu in Japan.


    continental temperate zone
    • Temperate continental climates are found on continents in the Northern
    Hemisphere between 40o-70o
    • Climate in these areas is controlled by the fact that they are not located
    near Oceans where temperatures are moderate.
    • Temperate continental climates are also called micro thermal climates,
    because they are located away from the Oceans. These climatic zones
    experience the extremes of temperatures.
    • Summers are warm and can be very humid while winters are cold with
    snowstorms and blustery winds.
    • The annual average temperatures are around 100 C.

    5.3.3 Cold zone
    5.3.3.1 Polar and Tundra climate
    The Tundra climate is found in the northern hemisphere beyond 60° N of the
    equator. These are areas to the North of Asia and Canada. It also occurs on the
    coast lands of Greenland. Polar climate is found in Greenland, interior of Iceland

    and in the Antarctica.


    Polar and Tundra climate
    Characteristics of Tundra climate
    • The average annual rainfall is 250 mm.
    • Precipitation is in the form of snow in winter and rainfall in summer.
    • Humidity is low because of low temperatures.
    • Winter temperatures are low. They range from - 29°c to 4°c. Summer
    temperatures average about 10°c.
    • Vegetation consists of mosses, lichens and dwarf trees and shrubs. It is
    called tundra vegetation.
    Characteristics of Polar climate
    • Temperatures are always low. They are below 0°c, which leads to snow.
    • Precipitation mainly occurs in summer. It averages between 100 mm
    and 250 mm.
    • Winters are associated with one continuous night. Summers are one
    continuous day.
    • Blizzards are common. These are snowstorms with high winds.
    Visibility is low.

    • There is hardly any vegetation. This is because of snow and ice cover.

    5.3.3.2 Mountain climate
    This type of climate is found in the mountain ranges of the world. These include
    Mt. Kenya, the Ethiopian Highlands and the Alpine ranges of Europe. Others are
    the North Western part of Rwanda, especially over volcanic region, the Andes
    of South America and the Rockies of North America.

    Characteristics of Mountain climate
    • High rainfall on the windward slopes. It is less on the leeward slopes,
    • Orographic rainfall is received,
    • Pressure and temperature decrease with altitude,
    • But if the mountains are high enough, there is a height at which
    maximum precipitation occurs and above which it decreases,
    • It is also characterized by strong local winds (mountain and valley

    breezes).


    Climate influences the distribution of population. This is because of temperature

    conditions, amount of precipitation and length of crop growing season.

    The relationship between climate and human activities is summarized below:
    i. Human activities in equatorial regions: Heavy rainfall and high
    temperatures support growth of forests. The main human activities are
    lumbering and agriculture. Lumbering is the cutting down of trees and
    making them into timber. Crops such as coffee grow well in this type of
    climate. Tourism is also developed in this area due to natural forest.

    ii. Human activities in savanna climate: This type of climate is good for
    agriculture and dairy farming. There is enough grass for the animals. Growing
    of vegetables is done in this type of climate.

    iii. Human activities in desert climate: The high temperatures and low
    rainfall are not supportive for agriculture. Animal keeping is also not well
    developed only camels, goats and sheep are kept in such type of climate.
    Furthermore, it is only around the oases that some farming is done. An
    oasis is a fertile spot in the desert where water is found. Growing of crops
    is done by irrigation. However, mining activities are done in some deserts
    for instance gold is extracted in West Australia; diamonds in the Kalahari
    and petroleum in Algeria, Libya, Saudi Arabia, Kuwait, Iran and Iraq.

    iv. Human activities in temperate climate: This type of climate is suitable
    for agriculture and livestock keeping. Most developed countries are in this
    type of climate. These zones have high population.

    v. Human activities in polar climate: The main activities in this zone are
    the fishing, hunting of seals in Greenland and tourism in Arctic Circle. Few
    people are found here.
    vi. Human activities in mountain climates: Due to rainfall in the windward,
    the main activities in this zone are agriculture (maize, wheat, coffee, and

    pyrethrum), tourism, animal rearing and mineral exploitation.


    ◄UNIT 4 SOILSUNIT 6 NATURAL VEGETATION OF THE WORLD►