Factors Affecting Climate
Every day we wear clothes after looking at the weather: cotton in summer, a sweater in the cold. How the weather is in a place over many years is studied under climate.
Climate is the average condition of temperature, rainfall and wind of a region over many years. Temperature, rainfall and wind are the elements of climate.
Key idea 1 : Latitude — Near the equator the Sun’s rays fall almost vertically, so temperature is high there. Away from the equator rays fall slant and temperature decreases. As Brazil has a great north-south extent, the north is hot while a temperate climate is found near the Tropic of Capricorn. In India the Tropic of Cancer passes through the middle of the country; so most of India lies in the tropical zone and temperature increases towards the south.
Key idea 2 : Altitude and distance from the sea — As we go higher temperature falls; so hilly regions are cooler. In the Brazilian Highlands the climate is cooler than the surrounding lowlands. Near the sea the air is humid and mild; away from the sea the air becomes dry and the difference between summer and winter increases. A comparative study of a coastal city like Mumbai and an inland city like Delhi is useful for this.
Key idea 3 : Winds and relief — Winds bring moisture from the sea; when blocked by a mountain they rise and cool, so rain falls on the windward slope and little rain on the other side; this is called a rain-shadow region. In India the western slope of the Western Ghats gets more rain and the east gets less. In Brazil the Great Escarpment blocks the south-east trade winds and the north-eastern part beyond it gets little rain.
- Easy : Why is it colder on a high mountain? — Temperature falls with height.
- Medium : Why mild near the sea? — Sea adds moisture and reduces temperature extremes.
- Exam-type : What is a rain-shadow region? — Dry side behind a mountain away from the winds.
In the figure: Four factors that affect climate.
La-Al-Se-Wi.
Climate and weather (daily condition) are not the same; climate is the average of many years.
Memory clue: Latitude, altitude, sea, winds. Memory clue: "La-Al-Se-Wi" — Latitude, Altitude, Sea, Winds.
Spot the difference
| Factor | Effect | Example |
|---|---|---|
| Latitude | Hot near the equator | Amazon valley |
| Altitude | Temperature falls with height | Brazilian Highlands |
| Relief and winds | Rain shadow forms | East of the Western Ghats |
Practice questions
- 1What is climate?
- 2Which are the elements of climate?
- 3What is the effect of latitude on climate?
- 4What is the effect of altitude on temperature?
- 5How does a rain-shadow region form?
- 6State the benefits of nearness to the sea on climate.
- 7Write the reason for the climatic difference between Mumbai and Delhi.
- 8Write how latitude affects Brazil and India.
Show answers (try them yourself first)
- 1Average condition of temperature, rainfall and wind over many years.
- 2Temperature, rainfall, wind.
- 3Hot near the equator; cooler farther away.
- 4Temperature falls as we go higher.
- 5Mountain blocks winds; less rain on the far side.
- 6Air mild and humid; small temperature range.
- 7Mumbai is near the sea, Delhi far from it.
- 8Brazil hot in north, temperate in south; India tropical because of the Tropic of Cancer.
Climate of Brazil
Summer in one city and cold in another at the same time can happen only in a big country. Brazil is so large that its north and south parts show different climates.
Most of Brazil lies in the tropical zone and the equator passes through its northern part. South-east and north-east trade winds bring rain here.
Key idea 1 : Temperature — The north is hot and the average temperature in the Amazon valley is about 25° to 28° C. In the highlands it is slightly lower. On the coast the air is mild and humid because of the sea. The southern part near the Tropic of Capricorn has a temperate climate and quite cold winters. Near the equator on the coast the temperature range is very small.
Key idea 2 : Rainfall and Drought Quadrilateral — The Amazon valley receives about 2,000 mm rainfall; the north-eastern coast gets about 1,000 to 1,200 mm. Winds come from the sea and are blocked by the highlands and escarpment, giving relief rainfall on the coastal area; beyond the highlands the effect of the winds decreases and very little rain falls there. This rain-shadow region is known as the ‘Drought Quadrilateral’.
Key idea 3 : Cyclones and snowfall — In the coastal areas near the equator winds rise almost vertically and the convergence zone of trade winds is weak; so Brazil is rarely hit by tropical cyclones. As Brazil is a tropical country it normally has no snowfall; but at times southern polar air masses cause snowfall in the south.
- Easy : Which part of Brazil is hottest? — North, Amazon valley.
- Medium : Why cyclones rarely in Brazil? — Weak convergence zone, winds rise vertically.
- Exam-type : When does it snow in Brazil? — When polar air reaches the south.
In the figure: Blocked winds create a rain-shadow region.
Major snowfall records in southern Brazil: 1879 (Vacaria), 1957 (Sao Joaquim) and 1985 (Itatiaia mountains) (as per several sources; check with the book).
Winds blocked, rain first, drought beyond.
Though in the tropics, Brazil is not hot everywhere; the highlands and the south are cooler.
Memory clue: Brazil = hot north, temperate south, dry north-east. Memory clue: "North hot, south cool, north-east dry".
Spot the difference
| Region | Climate | Rainfall |
|---|---|---|
| Amazon valley | Hot (25°–28° C) | About 2,000 mm |
| North-eastern coast | Hot, mild | 1,000–1,200 mm |
| Southern part | Temperate, cool winter | Moderate |
Practice questions
- 1Write the features of Brazil’s climate.
- 2Due to which winds does it rain in Brazil?
- 3What is the Drought Quadrilateral?
- 4Why is the risk of tropical cyclones low in Brazil?
- 5Why does snowfall not occur in Brazil always?
- 6Compare the climate of the Amazon valley and the highlands.
- 7Why is the temperature range of Manaus small?
- 8Prepare a table of climate regions of Brazil.
Show answers (try them yourself first)
- 1Hot north, temperate south, more rain in the Amazon, less in the north-east.
- 2Due to south-east and north-east trade winds.
- 3The rain-shadow low-rainfall region beyond the escarpment.
- 4Weak convergence zone and winds rise vertically.
- 5Brazil is tropical; snow only when polar air arrives.
- 6Valley hot and humid; highlands cooler.
- 7Near the equator and under the sea’s influence.
- 8Student prepares the table.
Climate of India: Monsoon
When June comes we bring out the umbrella because the rainy season starts. This rain comes from monsoon winds; ‘monsoon’ comes from the word for season.
India’s climate is of the monsoon type. The direction of winds changes with the season and rain falls accordingly. As per the India Meteorological Department there are four seasons: hot weather, monsoon, retreating monsoon and cold weather.
Key idea 1 : Temperature and role of the Himalayas — Sun’s rays are vertical up to the Tropic of Cancer; it passes through the middle of the country, so India has high average temperature throughout the year, increasing towards the south. In winter the temperature falls below zero in Jammu and Kashmir and the Himalayan mountainous parts. The Himalayas block very cold winds coming from the north and also stop monsoon winds causing rain; the Indian Ocean gives moisture to the winds.
Key idea 2 : South-west monsoon and rainfall — In summer the Punjab plains and the Thar Desert get very hot, so a low-pressure belt forms. Winds start blowing towards India from the high-pressure region over the Indian Ocean carrying moisture. Because of the obstruction by the Eastern and Western Ghats, it rains more in the coastal areas and less on the far side of the hills. These winds blow parallel to the Aravalis so rainfall is low in parts of Gujarat and Rajasthan. When they hit the Himalayas, orographic rain falls again.
Key idea 3 : Retreating monsoon, seasons and disasters — The returning winds after hitting the Himalayas move from the north-east towards the Indian Ocean and give rain again to some parts of the Peninsula; this is the retreating monsoon season. Tamil Nadu gets its maximum rainfall in this season. India frequently faces natural disasters like erratic rainfall, drought, cyclones and floods. Jaisalmer is in western Rajasthan and as per the textbook is the driest part of India (less than 120 mm rainfall annually).
- Easy : What are monsoon winds? — Winds that change direction with the season.
- Medium : Use of the Himalayas for climate? — Blocks cold winds and stops monsoon winds causing rain.
- Exam-type : When does Tamil Nadu get most rain? — In the retreating monsoon season.
In the figure: Low pressure in summer brings monsoon winds.
Mawsynram in Meghalaya (about 11,872 mm annual average) and Cherrapunji are among the wettest places in the world; Mawsynram is counted as the place with the highest average, but some places in Colombia dispute this claim (as per several sources; check with the book).
Heat → low pressure → winds → rain.
Rain is not equal everywhere in India; more near the Ghats and Himalayas, less in Rajasthan and beyond the Ghats.
Memory clue: Four seasons of India: hot, monsoon, retreating monsoon, cold. Memory clue: "Hot-Mon-Ret-Cold".
Spot the difference
| Season | Winds/cause | Result |
|---|---|---|
| Hot weather | Sun in northern hemisphere | Low pressure in north India |
| Monsoon | South-west monsoon winds | Rain over most of India |
| Retreating monsoon | Returning north-east winds | Rain in Tamil Nadu |
Practice questions
- 1Why is India’s climate called monsoon?
- 2How do the south-west monsoon winds form?
- 3Explain the importance of the Himalayas for climate.
- 4Explain the importance of the Indian Ocean for climate.
- 5State the four seasons of India.
- 6Why is rainfall low east of the Ghats?
- 7What is the retreating monsoon?
- 8Why is rainfall low in Rajasthan?
Show answers (try them yourself first)
- 1Winds change direction with seasons and bring rain.
- 2Moist sea winds move to the summer low pressure.
- 3Blocks cold winds; stops monsoon winds causing rain.
- 4Gives moisture to winds; origin of monsoon.
- 5Hot, monsoon, retreating monsoon, cold.
- 6It lies in the rain-shadow region.
- 7Returning winds that bring rain to the Peninsula again.
- 8Winds blow parallel to the Aravalis; no barrier.
Comparing the Climates of India and Brazil
To compare the climate of two cities we check three points: temperature, rainfall and winds. The same three points can be used for two countries.
Though both countries lie in the tropics, there are differences and similarities in their climates because of location, relief and winds.
Key idea 1 : Seasons and months — As India is in the northern hemisphere and Brazil mostly in the southern, seasons in the two countries are opposite. In India summer is March to May; in southern Brazil summer is December to February and winter June to August. In India monsoon rain falls from June to September, while in Brazil the rainy season is usually at the beginning and end of the year; in the Amazon region it rains throughout the year.
Key idea 2 : Rainfall and winds — Rainfall in India is due to the south-west and north-east monsoon winds and is orographic; convectional rain is not prominent here. In Brazil rain comes from the south-east and north-east trade winds. In India the Himalayas and Western Ghats decide the amount of rain; in Brazil the Great Escarpment and highlands. Both countries have rain-shadow areas: in India parts of Rajasthan and the regions east of the Ghats, in Brazil the Drought Quadrilateral.
Key idea 3 : Cyclones and disasters — India is frequently hit by cyclones, floods and droughts; Brazil rarely gets tropical cyclones, but floods and droughts occur there too. In India the temperature extremes are large (very hot in Rajasthan, very cold in the Himalayas); Brazil does not get such extreme cold as India, because it has no high mountains like the Himalayas.
- Easy : When is summer in India and southern Brazil? — March–May; December–February.
- Medium : Rain-shadow areas of both? — Parts of Rajasthan; Drought Quadrilateral.
- Exam-type : Where more cyclones? — In India.
In the figure: Comparison of the climates of India and Brazil.
Seasons opposite, rain shadow in both.
India and Brazil do not have the same season at the same time; seasons are opposite.
Memory clue: Comparison: seasons opposite, winds different, rain shadow in both. Memory clue: "Opposite seasons, same shadow".
Spot the difference
| Point | India | Brazil |
|---|---|---|
| Winds | Monsoon winds | Trade winds |
| Cyclones | Frequent | Rare |
| Rain shadow | Rajasthan, east of the Ghats | Drought Quadrilateral |
Practice questions
- 1Compare the climates of India and Brazil.
- 2Why are the seasons opposite in both countries?
- 3State the difference in rain-bringing winds of both countries.
- 4Why is the cyclone risk low in Brazil and high in India?
- 5Which are the rain-shadow regions of both countries?
- 6Why are temperature extremes large in India?
- 7How is the climate of both linked to the Tropic of Cancer/Capricorn?
- 8Write a note on directional differences in temperature and rainfall in India and Brazil.
Show answers (try them yourself first)
- 1Opposite seasons, different winds, cyclones, rain shadow in both.
- 2India in northern, Brazil mostly in southern hemisphere.
- 3Monsoon winds in India, trade winds in Brazil.
- 4In India cyclones form over seas and come; in Brazil convergence zone weak.
- 5Parts of Rajasthan and Drought Quadrilateral.
- 6Because of the Himalayas and the Thar Desert.
- 7Tropic of Cancer through middle of India, Tropic of Capricorn through south Brazil.
- 8Student writes the points.