CLIMATE OF WORLD
Climate holds an important place in our own life. Our life and various economic activities (agriculture, industries, commerce, etc.) are affected by climate. Climate has also an important place in physical geography.
Climate is a measure of the average pattern of variation in temperature, humidity, atmospheric pressure, wind, precipitation, atmospheric particle count and other meteorological variables in a given region over long periods of time. Any independent study of each of these elements does not present any comprehensive view of climate. On the basis of these elements, there could be thousands of types of climates in the world.
Weather and climate are the two terms used to express atmospheric conditions.
Weather refers to frequent changes or average conditions in the atmosphere of a place at a given time. It refers to conditions of temperature, pressure, winds, clouds, humidity, rainfall etc., eg. Cloudy weather in the morning, hot weather in the evening, etc.,
The scientific study of weather conditions is called ‘Meteorology’.
The Headquarters of the Indian Meteorological Department (IMD) is situated in Poona (Pune) of Maharashtra.
The average weather condition of a place for a long period like 30-33 years is known as climate. It refers to long durational changes in the atmospheric condition of a Country/Region/part of the Continent etc.
The scientific study of climate is known as ‘Climatology’.
Types of Climates
I. Tropical Climates
Tropical Monsoon Climate
The Savannah or Sudan Climate
Tropical Desert Climate
II. Sub-Tropical and Temperate Climates
Temperate Grassland Climate
III. Polar Climates
I. Tropical Climates
1. Equatorial Climate
The equatorial, hot, wet climate is found between 5° and 10° north and south of the equator.
Its greatest extent is found in the lowlands of the Amazon, the Congo, Malaysia and the East Indies.
Further away from the equator, the influence of the on-shore Trade Winds, gives rise to a modified type of equatorial climate with monsoonal influences.
There is great uniformity of temperature throughout the year.
The mean monthly temperatures are always around 24° to 27°C, with very little variation.
There is no winter.
Precipitation is heavy and well distributed throughout the year.
Annual average is always above 150 cm. In some regions the annual average may be as high as 250 – 300 cm.
There is no month without rain. The monthly average is above 6 cm most of the time.
There is much evaporation and convection air currents are set up, followed by heavy thunderstorms in the afternoons.
High temperature and abundant rainfall support a luxuriant tropical rainforest.
In the Amazon lowlands, the forest is so dense that it is called ‘selvas’.
The equatorial vegetation comprises a multitude of evergreen trees that yield tropical hardwood, e.g. mahogany, ebony, dyewoods etc.
In the coastal areas and brackish swamps, mangrove forests thrive.
Indian tribes of Amazon basin
Pygmies of Congo basin
Orang Asli of Malaysia
In the forests, most primitive people live as hunters and collectors and the more advanced ones practice shifting cultivation.
Some plantation crops are also practiced like natural rubber, cocoa, etc.
2. Tropical Monsoon Climate
Tropical Monsoon is found in the zones between 5° and 30° latitudes on either side of the equator.
It is best developed in the Indian subcontinent, Burma, Thailand, Laos, Cambodia, parts of Vietnam and South China and northern Australia.
Tropical Marine climate is found in Central America, West Indies, the Philippines, parts of East Africa, Madagascar, the Guyana coast and eastern Brazil.
Though the mean annual temperature is fairly high, summer and winter seasons are sharply differentiated due to northward and southward movement of the sun.
Average temperature of warm dry summer months ranges between 27°C and 32°C.
Most of their annual rainfall occurs through cyclonic and orographic types of rain.
The average annual rainfall is around 150 cm but there are many variations in the temporal and spatial distribution.
Most of the annual monsoonal rainfall is received through moisture laden South-West monsoon winds.
The natural vegetation of tropical monsoon lands depends on the amount of the summer rainfall.
Trees are normally deciduous.
The forest is open and less luxuriant.
Most of the forests yield valuable timber like teak. Other kinds of timber are sal, acacia and eucalyptus.
People are mainly engaged in agriculture.
The crops grown here include rice, wheat, pulses, cotton, jute, sugarcane, oilseeds, coffee, tea and various types of fruits and vegetables.
All types of domestic animals are reared in this region.
This region is highly developed in agriculture and other agro-based activities.
The region is also very rich in deposits of various types of minerals which are essential ingredients for modern industrial activities.
3. The Savannah or Sudan Climate
The Savannah or Sudan Climate is a transitional type of climate found between the equatorial forest and the hot deserts.
It is located between 50-200 latitudes on either side of the equator.
It is best developed in Sudan where the dry and wet seasons are most distinct, hence its name the Sudan Climate.
The belt includes West African Sudan, and then curves southwards into East Africa and southern Africa north of the Tropic of Capricorn.
In South America, there are two distinct regions of savannah located north and south of the equator, namely the Llanos of the Orinoco basin and the Campos of the Brazilian Highlands.
The Savanna climate is characterized by distinct wet and dry seasons. Mean high temperature throughout the year is between 24°C and 27°C.
The annual range of temperature is between 3°C and 8°C.
The extreme diurnal range of temperature is a characteristic of the Sudan type of climate.
The average annual rainfall ranges between 100 cm and 150 cm.
The prevailing winds of the region are the Trade Winds which bring rain to the coastal regions.
It is characterized by tall grass and short trees.
Trees are deciduous and hard.
The grass is tall and coarse like elephant grass.
Scrubland is well represented by a number of species in Australia like mallee, mulga, Spinifex grass, etc.
Many tribes live within the Savanna lands.
Some tribes live as pastoralists like the Masai and others as settled cultivators like the Hausa of northern Nigeria.
However, agriculture is not much developed.
4. Tropical Desert Climate
The major hot deserts of the world are located on the western coasts of continents between latitudes 15° and 30° N and S.
They include the Sahara Desert, the largest single stretch of desert, which is 3,200 miles from east to west and at least 1,000 miles wide.
The Great Australian Desert covers almost half of the continent.
The other hot deserts are the Arabian Desert, Iranian Desert, Thar Desert, Kalahari and Namib Deserts.
In North America, the desert extends from Mexico to the USA and is called by different names at different places, e.g. the Mojave, Sonoran, Californian and Mexican Dessert.
In South America, the Atacama or Peruvian Desert (rain shadow effect and off-shore trade winds) is the driest of all deserts with less than 2 cm of rainfall annually.
There is no cold season in the hot deserts and the average summer temperature is around 30ºC.
The diurnal range of temperature in the deserts is very great.
Intense insolation by day in a region of dry air and no clouds causes the temperature to rise with the sun.
But as soon as the sun sets, the land loses heat very quickly by radiation and the mercury levels drop.
In South America, the Atacama or Peruvian Desert is the driest of all deserts with less than 0.5 inches of rainfall annually.
The Patagonian Desert is more dry due to its rain shadow position on the leeward side of the lofty Andes than to continentality.
The hot deserts lie astride the Horse Latitudes or the Sub Tropical High-Pressure Belts where the air is descending, a condition least favorable for precipitation of any kind to take place.
The relative humidity is extremely low, decreasing from 60 percent in coastal districts to less than 30 percent in desert interiors.
Rain normally occurs as violent thunderstorms of the conventional type.
The deserts are some of the hottest spots on earth and have high temperatures throughout the year.
All deserts have some form of vegetation such as grass, scrub, herbs, weeds, roots, or bulbs.
The predominant vegetation of both hot and mid-latitude deserts is xerophytic or drought-resistant scrub.
This includes the bulbous cacti, thorny bushes, long-rooted wiry grasses, and scattered dwarf acacias.
It is home to primitive hunters and gatherers who do not cultivate any crops, or domesticate any animals.
They include the Bushmen of the Kalahari desert, Bindibu or the Aborigines of Australia.
The nomadic herdsmen pursue a livestock economy, wandering through the deserts along with their herds in search of water and green pastures.
They include Bedouins of Arabia, the Tuaregs of Sahara, the Mongols of Gobi desert.
The settled cultivators cultivate crops like wheat, barley, sugarcane, fruits and vegetables.
It is for gold mines in Australia, Diamond mines in Kalahari, Copper mines in Chile, Silver mines in Mexico, Oil in the Persian Gulf countries.
2. Sub-Tropical and Temperate Climates
1. Mediterranean Climate
Entirely confined to the western portion of continental masses, between 30° and 45° north and south of the equator.
The basic cause of this type of climate is the shifting of the wind belts.
Mediterranean Sea has the greatest extent of this type of ‘winter rain climate’, and gives rise to the name Mediterranean Climate.
The best developed form of this climatic type is found in central Chile.
Other Mediterranean regions include.
Clear skies and high temperatures; hot, dry summers and cool, wet winters.
Mean annual precipitation ranges from 35 – 90 cm.
Temperature of warmest month greater than or equal to 10⁰ C.
Temperature of coldest month is less than 18⁰ C but greater than –3⁰ C
Climate is not extreme because of cooling from water bodies.
Trees with small broad leaves are widely spaced and never very tall.
The absence of shade is a distinct feature of Mediterranean lands.
Plants are in a continuous struggle against heat, dry air, excessive evaporation and prolonged droughts. They are, in short xerophytic [drought tolerant], a word used to describe the drought-resistant plants in an environment deficient in moisture.
The area is important for fruit cultivation, cereal growing, wine-making and agricultural industries as well as engineering and mining.
2. The Temperate Grassland (Steppe) Climate
They lies in the interiors of the continents.
Lie in the Westerly wind belt [mid-latitudes or temperate region].
Grasslands are practically treeless due to continentiality [deep within the interiors of the continents where rain bearing winds don’t reach].
In Eurasia, they are called the Steppes, and stretch eastwards from the shores of the Black Sea to the foothills of the Altai Mountains. [2,000 miles long belt].
Climate is continental with extremes of temperature.
Temperatures vary greatly between summer and winter.
The summers are hot and the winters are cold.
Summers are very warm, over 18 – 20° C.
The steppe type of climate in the southern hemisphere is never severe.
The average rainfall may be taken as about 45 cm, but this varies according to location from 25 cm to 75 cm.
The heaviest rain comes in June and July (late spring and early summer).
Most of the winter months have about an 2.5 cm of precipitation, brought by the occasional depressions of the Westerlies and coming in the form of snow.
The maritime influence in the southern hemisphere causes more rainfall.
The reference to steppe grassland is taken to mean the temperate grasslands of the mid-latitudes, the Steppes, Prairies, Pampas, Veld and Downs.
The steppes are grass-covered, differing only in the density and quality of the grass.
Their greatest difference from the tropical savannah is that they are practically treeless and the grasses are much
Where the rainfall is moderate, above 20 inches, the grasses are tall, fresh and nutritious and are better described as long prairie grass.
The appearance of the temperate grasslands varies with seasons. Trees are very scarce in the steppes, because of the scanty rainfall, long droughts and severe winters.
The grasslands have been ploughed up for extensive, mechanized wheat cultivation and are now the ‘granaries of the world’. Besides wheat, maize is increasingly cultivated in the warmer and wetter areas. The tufted grasses have been replaced by the more nutritious Lucerne or alfalfa grass.
III. Polar Climates
1. Taiga Climate
It stretches along a continuous belt across central Canada, some parts of Scandinavian Europe and most of central and southern Russian. [50° to 70° N].
Found only in the northern hemisphere [due to great east-west extent. Absent in the southern hemisphere because of the narrowness in the high latitudes].
Experienced in the regions just below the Arctic circle.
On its poleward side, it merges into the Arctic tundra.
The climate fades into the temperate Steppe climate.
Summers are brief and warm reaching 20-25 °C whereas winters are long and brutually cold – always 30-40 °C below freezing.
Annual temperature range of the Siberian Climate is the greatest [Almost 50-60 °C in Siberia].
Some of the lowest temperatures in the world are recorded in Verkhoyansk (68°N. 113°E) where -67 °C was once recorded.
In North America, the extremes are less severe, because of the continent’s lesser east-west stretch.
All over Russia, nearly all the rivers are frozen. In normal years, the Volga is ice-covered for about 150 days.
Occasionally cold, northerly polar local winds such as the blizzards of Canada and the buran of Eurasia blow violently.
Maritime influence in the interiors is absent.
Frontal disturbances might occur in winter.
Typical annual precipitation ranges from 38 cm to 63 cm.
It is quite well distributed throughout the year, with a summer maxima [convectional rain in mid-summer – 15 °C to 24 °C]
In winter the precipitation is in the form of snow, as mean temperatures are well below freezing all the time.
The predominant vegetation is evergreen coniferous forest.
The conifers, which require little moisture are best suited to this type of sub-Arctic climate.
The greatest single band of the coniferous forest is the taiga (a Russian word for coniferous forest) in Siberia.
In Europe the countries that have a similar type of climate and forests are Sweden and Finland.
There are small amounts of natural coniferous forest in Germany, Poland, Switzerland, Austria and other parts of Europe.
In North America, the belt stretches from Alaska across Canada into Labrador.
Lot of coniferous forests in the northern hemisphere are still untouched due to remoteness.
Only a small fraction of coniferous forests in Canada, Russia etc. are exploited leaving a huge potential for the future.
More accessible forests are cleared for lumbering on a large scale.
Agriculture is most unlikely as few crops can survive in the sub-Arctic climates
2. Tundra Climate
Found in regions north of the Arctic Circle and south of Antarctic Circle.
The ice-caps are confined to highlands and high latitude regions of Greenland and Antarctica.
In the southern hemisphere, Antarctica is the greatest single stretch of ice-cap (10,000 feet thick).
The lowlands – coastal strip of Greenland, the barren grounds of northern Canada and Alaska and the Arctic seaboard of Eurasia, have tundra climate.
The tundra climate is characterized by a very low mean annual temperature.
In mid-winter temperatures are as low as 40 – 50 °C below freezing.
Summers are relatively warmer.
Normally not more than four months have temperatures above freezing-point.
Within the Arctic and Antarctic Circles, there are weeks of continuous darkness (Rotation and Revolution).
The ground remains solidly frozen and is inaccessible to plants.
Frost occurs at any time and blizzards, reaching a velocity of 130 miles an hour are not infrequent.
Precipitation is mainly in the form of snow and sleet.
Convectional rainfall is generally absent.
There are no trees in the tundra.
Lowest form of vegetation like mosses, lichens etc. are found here and there.
Climatic conditions along the coastal lowlands are a little favorable.
Coastal lowlands support hardy grasses and the reindeer moss which provide the only pasturage for reindeers.
In the brief summer, berry-bearing bushes and Arctic flowers bloom.
In the summer, birds migrate north to prey on the numerous insects which emerge when the snow thaws.
Mammals like the wolves, foxes, musk-ox, Arctic hare and lemmings also live in tundra regions.
Penguins live only in Antarctic regions.