Short & Long Question Answer: Climate

Q1: Distinguish between weather and climate.
Ans: The main difference between weather and climate is the time period over which atmospheric conditions are measured. Weather refers to short-term atmospheric conditions; climate refers to long-term average patterns.

• Weather describes the state of the atmosphere at a particular place over a short period - from minutes to days. It includes conditions such as temperature, humidity, rainfall, cloudiness and wind at that time.
• Climate is the average pattern of weather observed at a place over a long period, typically 30 years. It summarises what the weather is usually like - for example, whether a region is generally hot, cold, wet or dry.
• Weather can change from hour to hour or day to day, while climate changes slowly and is described by long-term trends and averages.
• Example: It may rain (weather) on a single day in Delhi, but Delhi's climate is described as having very hot summers and cool winters over many years.

Q2: What are western cyclonic disturbances?
Ans: Western cyclonic disturbances are extra-tropical low-pressure systems that originate over the Mediterranean region and move eastwards with the westerly winds. They affect north and north-western India mainly in winter and early spring.

• These disturbances travel across West Asia and bring cloudiness, rain and often snowfall to the Himalayan region and adjoining plains.
• They are responsible for winter precipitation in north India and sometimes cause cold waves in the plains.
• Their arrival is important for winter crops and for relieving very cold conditions in the region.

Q3: What is known as the Southern Oscillation or SO? Mention the feature connected with it.
Ans: The Southern Oscillation is a periodic change in air pressure across the tropical Pacific and surrounding oceans. It involves alternating high and low pressure between the eastern and western parts of the tropical Pacific and is closely linked with El Niño and La Niña events.

• A key feature connected with the Southern Oscillation is ENSO (El Niño-Southern Oscillation): during El Niño, warm ocean waters spread eastwards along the South American coast and are associated with weaker Indian monsoons; during La Niña, cooler waters and stronger monsoons may occur.
• Changes in these pressure and ocean temperature patterns influence rainfall and temperature in many parts of the world, including India.

Q4: Withdrawal of the monsoon is a gradual process. Explain.
Ans: The withdrawal of the monsoon from India happens in stages rather than all at once. It is controlled by the cooling of the land, changes in pressure systems and the retreat of the monsoon trough.

• Withdrawal begins in the north-west of India from early September and progresses south-eastwards.
• By mid-October, the monsoon withdraws from the northern half of the peninsula; withdrawal from the southern half is faster and is usually complete by early December.
• The process is gradual because the monsoon trough and low-pressure systems retreat slowly and different regions respond at different times depending on local topography and pressure changes.

Q5: The breaks in the monsoon are related to the movement of the monsoon trough. Explain.
Ans: Breaks in the monsoon occur when the monsoon trough shifts position and weakens, causing reduced rainfall over regions that had been receiving rain.

• The monsoon trough is an elongated low-pressure zone over the plains. When its axis lies over a region, that region receives good rainfall.
• When the trough shifts northwards towards the Himalayas or weakens, the plains experience dry spells or "breaks" while rainfall becomes concentrated over the mountain catchments.
• Thus, movement of the trough controls the timing and distribution of rainy and dry phases during the monsoon season.

Q6: How do the frequency and intensity of tropical depressions determine the amount and duration of monsoon rains?
Ans: Tropical depressions, especially those forming over the Bay of Bengal, play a major role in producing heavy rainfall during the monsoon. Their number and strength affect both the quantity and persistence of rain.

• Frequent and intense depressions bring widespread and heavy rainfall, increasing total seasonal rainfall and prolonging wet spells.
• If depressions are few or weak, rainfall may be below normal and long dry spells can occur, reducing the duration and amount of effective monsoon rain.
• Depressions generally follow the monsoon trough and carry large amounts of moisture from the ocean into the interior, so their path and speed also affect where and how long the rain falls.

Q7: Give a brief description of the distribution of rainfall in India.
Ans: The distribution of rainfall in India is highly uneven, varying widely from one region to another.

• The western coasts (windward side of the Western Ghats) and the northeastern hills receive very heavy rainfall - in many places over 400 cm annually.
• Regions such as western Rajasthan, parts of Gujarat, Haryana and Punjab receive low rainfall - often less than 60 cm per year.
• The interior of the Deccan plateau and the eastern slopes of the Sahyadris also receive relatively low rainfall.
• Some high-altitude cold deserts, for example Leh in Jammu and Kashmir, receive very little precipitation.
• Most other parts of the country receive moderate rainfall, while snowfall is restricted mainly to the higher Himalayas.

Q8: What do you mean by the southwest monsoon? Explain in brief.
Ans: The southwest monsoon is the seasonal wind system that blows from the south-west over the Indian subcontinent during the summer months and brings the main rainy season to most parts of India.

• Intense heating of the land, especially over the Thar Desert and north-west India, creates a low-pressure area which draws moisture-laden winds from the Arabian Sea and Bay of Bengal.
• These winds are forced to rise over the Western Ghats and the Himalayas, causing cooling and condensation of moisture and resulting in heavy rainfall.
• The southwest monsoon supplies the majority of India's annual rainfall and is crucial for agriculture and water resources.

Q9: What is known as the North East Monsoon or Retreating Monsoon? Explain in brief.
Ans: The North East Monsoon, or retreating monsoon, occurs after the southwest monsoon withdraws. It involves winds blowing from the north-east towards the equator and affects mainly the south-eastern coast of India.

• As the Indian landmass cools from September onwards, a high-pressure area develops and winds reverse to blow from land to sea in a north-easterly direction.
• These winds pick up moisture from the Bay of Bengal and bring rainfall to Tamil Nadu, parts of Andhra Pradesh and southern Tamil Nadu during October-December.
• Unlike the southwest monsoon, the retreating monsoon gives most of its rain to the south-east coast rather than the western coast.

Q10: What are the characteristic features of a retreating monsoon?
Ans: Key features of the retreating monsoon are listed below.

• As the sun moves south after the summer, the low-pressure trough over the northern plains weakens and a high-pressure system gradually establishes. This causes the southwest monsoon winds to weaken and withdraw.
• The months of October-November form a transition from the hot-rainy season to the dry winter. Skies clear in many places, and daytime temperatures may remain high while nights become cooler and pleasant.
• The land remains moist soon after withdrawal, so humidity can make daytime weather feel oppressive for a short period. In the second half of October, temperatures fall rapidly in northern India.
• Low-pressure conditions shift towards the Bay of Bengal by early November. Cyclonic depressions forming over the Andaman Sea often move across the eastern coast, causing heavy and widespread rainfall along the east coast.

Q11: Describe briefly what you know about the onset of monsoon and its withdrawal.
Ans: The Indian climate is largely monsoon dominated. The monsoon arrives and withdraws in a characteristic pattern influenced by pressure systems, topography and seasonal heating.

• The southwest monsoon is pulsating in nature and lasts roughly 100-120 days from early June to mid-September.
• The monsoon usually reaches the southern tip of India in the first week of June and then splits into two branches: the Arabian Sea branch and the Bay of Bengal branch.
• The Arabian Sea branch reaches Mumbai around 10 June and advances fairly rapidly north-westwards and inland, while the Bay of Bengal branch moves northwards to reach Assam in early June and then spreads westwards over the Gangetic plains.
• By mid-June, the Arabian Sea branch reaches Saurashtra-Kutch and central India; by mid-July the monsoon covers Himachal Pradesh and most of the country.
• Withdrawal begins from the north-western states in early September and by mid-October the monsoon has withdrawn from the northern half of the peninsula; the rest of the country becomes dry by early December.

Q12: What are the factors that affect India's climate? Describe them.
Ans: The major factors affecting India's climate include latitude, altitude, and pressure and wind systems. A brief description of each follows.

• Latitude: India lies between the equator and the temperate zone with the Tropic of Cancer passing through its middle. Southern areas are tropical while northern parts are sub-tropical, causing differences in solar heating and temperature.
• Altitude: Temperature falls with height, so higher regions such as the Himalayas and other hill areas are cooler than the plains. Altitude also influences rainfall and local climate.
• Pressure and winds: Seasonal changes in pressure over land and ocean cause wind reversal. In winter, high pressure over northern India brings dry cold winds; in summer, low pressure draws moist winds from the Indian Ocean, producing the monsoon.

Air also moves from the high-pressure area over the southern Indian Ocean in a south-easterly direction, crosses the equator and bends rightwards to reach the Indian subcontinent as the southwest monsoon. Upper-air circulation, western cyclonic disturbances and tropical cyclones further influence India's climate.

Q13: Give a brief description of the controls that affect India's climate.
Ans: There are six principal controls of India's climate: latitude, altitude, pressure and wind system, distance from the sea, ocean currents and relief. A short explanation of each is given below.

• Latitude: Latitude determines how much solar energy a place receives. Regions nearer the equator are warmer, while those farther north are cooler.
• Altitude: Higher places have thinner air and lower temperatures, giving hill stations cooler summers and colder winters.
• Pressure and wind system: These control the direction and strength of winds and hence the temperature and rainfall patterns - for example, the seasonal reversal that produces the monsoon.
• Distance from the sea: Oceans moderate temperature. Coastal areas generally have milder climates, while interior regions, far from the sea, experience more extreme temperatures.
• Ocean currents: Warm or cold currents influence coastal climates when onshore winds blow. They can raise or lower coastal temperatures and affect rainfall patterns.
• Relief: Mountain ranges act as barriers to winds, cause orographic rainfall on windward slopes and create rain shadows on the leeward side, affecting local climates.

Q14: State the factors that help in understanding the mechanism of monsoon.
Ans: The following factors explain how the monsoon develops and behaves:

• The differential heating and cooling of land and sea, which creates low pressure over the heated land and relatively higher pressure over the surrounding seas.
• The northward shift of the Inter-Tropical Convergence Zone (ITCZ) over the Ganga plain in summer; during the monsoon this trough acts as the monsoon trough.
• The presence and position of a high-pressure area east of Madagascar (about 20°S) over the Indian Ocean, which influences the strength and path of the monsoon winds.
• Intense heating of the Tibetan plateau in summer produces strong vertical air currents and contributes to the formation of low pressure aloft, strengthening the monsoon circulation.
• The movement of the subtropical westerly jet stream north of the Himalayas and the development of a tropical easterly jet over the peninsula during summer.
• Changes in pressure conditions over the southern oceans (for example those associated with ENSO) that modify the monsoon's strength and timing.

Q15: Differentiate between southwest monsoon and northeast monsoon.
Ans: Both monsoons are seasonal wind systems but they differ in timing, direction, source of moisture and regions affected.

• Southwest Monsoon (summer monsoon): Occurs from June to September. Winds blow from the Arabian Sea and Bay of Bengal towards the heated landmass of India, bringing widespread rainfall to most parts of the country. It is driven by a strong thermal low over north-west India and the reversal of wind direction over the Indian Ocean.
• Northeast Monsoon (retreating monsoon): Occurs mainly from October to December. Winds blow from the north-east towards the equator and pick up moisture from the Bay of Bengal, giving significant rainfall to Tamil Nadu, parts of Andhra Pradesh and south-eastern India. This monsoon is less extensive than the southwest monsoon and mainly affects the south-eastern coast.
• The southwest monsoon is the principal source of India's annual rainfall; the northeast monsoon supplies much of the remaining seasonal rainfall mainly to the south-east coast.