Climate

Correct answer: (b) Mawsynram

Mawsynram, located in the Meghalaya plateau (East Khasi Hills), receives the highest rainfall in the world — approximately 1141 cm annually. It has surpassed Cherrapunji (which was previously considered the wettest place) due to its position on the windward side of the hills that forces the moisture-laden Bay of Bengal branch of the south-west monsoon to rise and precipitate heavily.

Correct answer: (b) Loo

During the hot weather season (May–June), very hot, dry, and dust-laden winds blow in the afternoon over the northern plains of India. These winds are called 'Loo'. They blow from the west and north-west and can be dangerous to human health, sometimes causing heat strokes.

Correct answer: (c) Early June

The south-west monsoon normally arrives at the Kerala coast (the southernmost tip of the Indian mainland) by the 1st of June. From there it advances northward and covers the entire country by mid-July. Hence, the monsoon arrives in India approximately in early June.

Correct answer: (b) Warm days and cold nights

During the cold weather season (December–February), the sun's rays are oblique over India. Days are relatively warm because of sunshine, but nights are cold because the clear skies allow the heat absorbed during the day to radiate back quickly into the atmosphere. Hence, the cold season is characterised by warm days and cold nights.

Given: We need to identify the factors (controls) that affect the climate of India.

Answer:

The following six major controls affect the climate of India:

1. Latitude: India lies between 8°4'N and 37°6'N. The Tropic of Cancer divides the country into two halves — the tropical region in the south and the sub-tropical region in the north. The southern part has a hot climate throughout the year while the northern part experiences extremes of temperature.

2. Altitude: India has mountains in the north (the Himalayas) and a vast coastal plain in the south. Places at higher altitudes are cooler than places at lower altitudes. The Himalayas prevent cold winds from Central Asia from entering India.

3. Pressure and Winds: The pressure and wind systems over India are influenced by the pressure conditions over Central Asia and the Indian Ocean. The seasonal reversal of winds (monsoons) is the most dominant feature.

4. Distance from the Sea (Continentality): Coastal areas have an equable (moderate) climate due to the moderating influence of the sea. Interior parts of India, far from the sea, experience extreme climate (very hot summers and very cold winters).

5. Ocean Currents: The warm ocean currents along the coast influence the temperature and rainfall of coastal areas.

6. Relief (Topography): Mountains and plateaus influence the distribution of rainfall. The Western Ghats and the Himalayas act as barriers and force the moisture-laden winds to rise, causing heavy orographic rainfall on the windward side and creating rain shadows on the leeward side.

Given: We need to explain why India has a monsoon type of climate.

Answer:

India has a monsoon type of climate due to the following reasons:

1. Location in the Tropics: India is located in the tropical region where the monsoon circulation is dominant.

2. Differential Heating of Land and Sea: During summer, the large landmass of the Indian subcontinent heats up much faster than the surrounding Indian Ocean. This creates a low-pressure area over the land and a high-pressure area over the sea. Moisture-laden winds blow from the sea towards the land — this is the south-west monsoon.

3. Seasonal Reversal of Winds: In winter, the land cools faster than the sea. High pressure develops over land and low pressure over the sea. Winds blow from land to sea — this is the north-east monsoon. This seasonal reversal of wind direction is the defining characteristic of a monsoon climate.

4. Role of the Himalayas: The Himalayas act as a barrier and prevent the monsoon winds from escaping northward, forcing them to shed their moisture over the Indian subcontinent.

5. Shift of ITCZ: The Inter-Tropical Convergence Zone (ITCZ) shifts northward in summer over the Ganga plain, attracting the trade winds from the Southern Hemisphere, which cross the equator and blow as the south-west monsoon.

Thus, the combination of these factors gives India a typical monsoon type of climate characterised by a distinct rainy season, a dry season, and seasonal reversal of winds.

Given: We need to identify the part of India with the highest diurnal range of temperature and explain the reason.

Answer:

Part of India: The Thar Desert region of Rajasthan (and other interior desert/semi-arid areas of north-western India) experiences the highest diurnal range of temperature.

Reasons:

1. Sandy soil: Sandy soil heats up very quickly during the day and loses heat very rapidly at night, causing extreme temperatures in both day and night.

2. Absence of vegetation: There is very little vegetation cover to moderate the temperature.

3. Absence of moisture/cloud cover: The sky remains clear (no clouds) both during the day and at night. During the day, the sun's rays heat the surface intensely. At night, without cloud cover, the heat radiates back quickly into the atmosphere, making nights very cold.

4. Distance from the sea: Being far from the sea, there is no moderating maritime influence.

As a result, the diurnal (day-night) range of temperature can be as high as 30°C to 40°C in these desert regions.

Given: We need to identify the winds responsible for rainfall along the Malabar coast.

Answer:

The Arabian Sea branch of the South-West Monsoon accounts for rainfall along the Malabar coast (the western coastal plain of Kerala and Karnataka).

Explanation:
- The south-west monsoon has two branches: the Arabian Sea branch and the Bay of Bengal branch.
- The Arabian Sea branch is stronger and carries more moisture. It strikes the Western Ghats almost perpendicularly.
- The Western Ghats force these moisture-laden winds to rise (orographic lifting), causing very heavy rainfall on the windward (western) side — the Malabar coast.
- This is why the Malabar coast receives very heavy rainfall (over 250 cm) during the monsoon season.
- The leeward side (Deccan Plateau) remains relatively dry — this is called the rain shadow area.

Given: We need to define monsoons and explain the concept of 'break' in monsoon.

Definition of Monsoon:

The word 'monsoon' is derived from the Arabic word 'mausim' which means season. Monsoons refer to the seasonal reversal of wind direction — winds blow from sea to land during summer (bringing rainfall) and from land to sea during winter. In India, the south-west monsoon (June to September) brings the bulk of the annual rainfall.

'Break' in Monsoon:

During the south-west monsoon season, there are wet and dry spells (periods of rain and no rain). These dry spells are called 'breaks' in the monsoon.

- During a break, the monsoon trough (low-pressure zone) shifts northward towards the foothills of the Himalayas.
- Rainfall occurs in the sub-Himalayan belt while the rest of the country remains dry.
- After a few days, the trough shifts back southward and rainfall resumes over the plains.
- These breaks can last for a few days to a few weeks.
- Prolonged breaks can lead to drought conditions in parts of the country.

Thus, the monsoon is not a continuous phenomenon — it has active phases (heavy rain) and break phases (little or no rain).

Given: We need to explain why the monsoon is considered a unifying bond for India.

Answer:

The monsoon is considered a unifying bond for the following reasons:

1. Common rainfall pattern: Despite regional variations in temperature and relief, the monsoon provides rainfall to almost the entire country during the same season (June to September), giving India a common climatic experience.

2. Agricultural calendar: The entire agricultural calendar of India revolves around the monsoon. Farmers across the country — from north to south and east to west — depend on the monsoon for their Kharif crops. This creates a shared agricultural rhythm.

3. River systems: The monsoon feeds all the major river systems of India. These rivers, carrying monsoon water, unite different regions of the country.

4. Cultural unity: The arrival of the monsoon is celebrated across India through festivals, songs, dances, and special food preparations. This creates a shared cultural experience that transcends regional differences.

5. Eagerly awaited: People across the entire country eagerly await the arrival of the monsoon, creating a sense of shared anticipation and unity.

6. Sets life in motion: The monsoon sets agricultural activities in motion across the country simultaneously, binding the lives of people together.

Thus, despite India's great diversity in landscape, language, and culture, the monsoon acts as a unifying bond that gives the country a common climatic identity.

Given: We need to explain why rainfall decreases from east to west in Northern India.

Answer:

Rainfall decreases from east to west in Northern India due to the following reasons:

1. Direction of the Bay of Bengal branch of the monsoon: The Bay of Bengal branch of the south-west monsoon enters India from the north-east (through the Brahmaputra valley and the north-eastern states). It then moves westward along the Ganga plains.

2. Progressive loss of moisture: As the Bay of Bengal branch moves westward across the Northern Plains, it sheds its moisture progressively. By the time it reaches western Uttar Pradesh, Haryana, Punjab, and Rajasthan, it has already lost most of its moisture. Hence, rainfall decreases from east to west.

3. Distance from the sea: Eastern parts of Northern India (West Bengal, Bihar) are closer to the Bay of Bengal and receive more moisture. Western parts (Rajasthan, Punjab) are farther from the sea and receive less moisture.

4. Weakening of the Arabian Sea branch: The Arabian Sea branch, after crossing the Western Ghats, loses most of its moisture. The remaining moisture it carries northward is not sufficient to cause heavy rainfall in western Rajasthan.

5. Aravalli Mountains: The Aravalli range runs parallel to the direction of the Arabian Sea branch of the monsoon, so it does not act as a barrier to force the winds to rise and precipitate. This further reduces rainfall in Rajasthan.

Result: Kolkata receives about 160 cm of rainfall, Patna about 105 cm, Allahabad about 76 cm, Delhi about 56 cm, and Jodhpur only about 36 cm — clearly showing the decrease from east to west.

Given: We need to explain why seasonal reversal of wind direction occurs over the Indian subcontinent.

Answer:

Seasonal reversal of wind direction takes place over the Indian subcontinent due to differential heating and cooling of land and sea across seasons:

In Summer (June–September):
- The large landmass of the Indian subcontinent heats up rapidly due to the high angle of the sun.
- A strong low-pressure area develops over the Thar Desert and the north-western plains.
- The Indian Ocean (especially the Arabian Sea and Bay of Bengal) remains relatively cooler, creating high pressure over the sea.
- Winds blow from the high-pressure area (sea) to the low-pressure area (land) — these are the south-west monsoon winds (sea to land).

In Winter (December–February):
- The landmass cools rapidly while the sea retains heat longer.
- High pressure develops over Central Asia and the Indian subcontinent.
- Low pressure develops over the warm Indian Ocean.
- Winds blow from land to sea — these are the north-east trade winds (land to sea), which are dry and bring little rainfall (except to the Tamil Nadu coast).

This complete reversal of wind direction between summer and winter is the fundamental characteristic of the monsoon climate, and it is caused by the differential heating and cooling of the land and sea.

Given: We need to explain why most of India's rainfall is concentrated in a few months.

Answer:

The bulk of rainfall in India is concentrated over a few months (June to September) due to the following reasons:

1. Monsoon mechanism: India's rainfall is almost entirely dependent on the south-west monsoon, which blows only during the summer months (June to September). This is a seasonal phenomenon lasting only about 4 months.

2. Dry conditions in other seasons: During winter (October to February), the north-east trade winds blow from land to sea. These winds are dry (they pick up little moisture over land) and bring very little rainfall to most parts of India.

3. Hot dry season: During the hot weather season (March to May), the weather is hot and dry. Occasional pre-monsoon showers (like Mango showers in Kerala and Karnataka, and Kaal Baisakhi in West Bengal) occur but are not widespread.

4. Retreating monsoon: The retreating monsoon (October–November) brings some rainfall to the Tamil Nadu coast and parts of south-eastern India, but this is limited in extent.

5. Geographical position: India's tropical location means it does not receive significant winter rainfall from the westerly disturbances except in the north-western parts (Punjab, Haryana) which receive some winter rain from western disturbances.

Thus, about 75–90% of India's annual rainfall is received during the four monsoon months of June to September.

Given: We need to explain why the Tamil Nadu coast receives rainfall in winter.

Answer:

The Tamil Nadu coast receives winter rainfall due to the following reasons:

1. North-East Monsoon (Retreating Monsoon): During October–December, the south-west monsoon retreats from the Indian subcontinent. The winds now blow from the north-east (from land to sea) — these are called the north-east monsoon or retreating monsoon.

2. Moisture from the Bay of Bengal: As the north-east trade winds blow from the land towards the sea, they pass over the Bay of Bengal and pick up moisture from it.

3. Orientation of the Tamil Nadu coast: The Tamil Nadu coast (Coromandel coast) faces the Bay of Bengal and lies in the path of these moisture-laden north-east winds. When these winds strike the Tamil Nadu coast, they cause rainfall.

4. Rain shadow during south-west monsoon: During the south-west monsoon season, Tamil Nadu lies in the rain shadow area of the Western Ghats. The Arabian Sea branch of the south-west monsoon loses most of its moisture on the western side of the Ghats. The Bay of Bengal branch moves parallel to the Tamil Nadu coast and does not cause much rainfall there. Hence, Tamil Nadu receives little rainfall during the south-west monsoon.

5. Cyclones: The Bay of Bengal is prone to cyclones during October–November, which also bring heavy rainfall to the Tamil Nadu coast.

Thus, while most of India receives rainfall during June–September, Tamil Nadu receives most of its rainfall during October–December (winter months).

Given: We need to explain why the delta region of the eastern coast is frequently struck by cyclones.

Answer:

The delta region of the eastern coast (deltas of the Mahanadi, Godavari, Krishna, and Kaveri rivers) is frequently struck by cyclones due to the following reasons:

1. Warm Bay of Bengal waters: The Bay of Bengal has warm surface waters, especially during October–November (post-monsoon season). Warm water provides the energy needed for the formation and intensification of tropical cyclones.

2. Shallow and enclosed nature of the Bay of Bengal: The Bay of Bengal is relatively shallow and semi-enclosed. This allows cyclones to intensify rapidly as they move towards the coast.

3. Low-lying delta regions: The delta regions are flat and low-lying, making them extremely vulnerable to storm surges (walls of water pushed by cyclones). There are no natural barriers to protect these areas.

4. Funnel-shaped coastline: The shape of the Bay of Bengal acts like a funnel — as cyclones move northward or north-westward, the narrowing of the bay concentrates the storm's energy, increasing its destructive power.

5. Retreating monsoon season: During October–November, when the south-west monsoon retreats, the conditions in the Bay of Bengal are particularly favourable for cyclone formation — warm sea surface temperatures, high humidity, and low wind shear.

6. Frequency of cyclones: The Bay of Bengal accounts for about 7% of the world's tropical cyclones, and many of these make landfall on the eastern coast of India.

Thus, the combination of warm sea waters, the geography of the Bay of Bengal, and the low-lying nature of the delta regions makes them highly vulnerable to cyclones.

Given: We need to explain why parts of Rajasthan, Gujarat, and the leeward side of the Western Ghats are drought-prone.

Answer:

Parts of Rajasthan and Gujarat:

1. Distance from the sea: These regions are far from the moisture source (the sea), so the monsoon winds lose most of their moisture before reaching here.

2. Aravalli Mountains run parallel: The Aravalli range runs parallel to the direction of the Arabian Sea branch of the monsoon. It does not act as a barrier to force the winds to rise and precipitate. Hence, the monsoon passes over Rajasthan without causing significant rainfall.

3. Hot desert conditions: The Thar Desert in Rajasthan creates a hot, dry environment. The high temperatures cause rapid evaporation of any moisture that does arrive.

4. Low rainfall: These areas receive less than 20–25 cm of annual rainfall, making them highly drought-prone.

Leeward side of the Western Ghats:

1. Rain shadow effect: The Western Ghats act as a barrier to the Arabian Sea branch of the south-west monsoon. The moisture-laden winds rise on the windward (western) side, cool down, and shed their moisture as heavy rainfall on the Malabar coast.

2. Dry descending air: After crossing the Western Ghats, the winds descend on the leeward (eastern) side. Descending air warms up and its relative humidity decreases, making it dry. This creates a rain shadow zone on the Deccan Plateau.

3. Less rainfall: The leeward side receives only 50–70 cm of rainfall compared to over 250 cm on the windward side.

Thus, both geographical location and topography make these regions drought-prone.

Given: We need to describe the regional variations in the climatic conditions of India.

Answer:

Although India has a broadly monsoon type of climate, there are significant regional variations in temperature, rainfall, and seasons. These can be described as follows:

1. Temperature Variations:

- North vs. South: In winter, the temperature in Drass (Ladakh) can fall to $-45°C$, while Thiruvananthapuram (Kerala) remains warm at about $22°C$. In summer, Rajasthan may record temperatures above $50°C$, while Pahalgam (Kashmir) remains cool at about $20°C$.

- Coastal vs. Interior: Coastal cities like Mumbai and Chennai have an equable (moderate) climate with small annual and diurnal ranges of temperature. Interior cities like Delhi and Nagpur experience extreme temperatures — very hot summers and cold winters.

2. Rainfall Variations:

- Highest rainfall: Mawsynram in Meghalaya receives over 1141 cm of annual rainfall — the highest in the world. The Malabar coast and the north-eastern states also receive very heavy rainfall (over 200 cm).

- Lowest rainfall: The Thar Desert in Rajasthan and parts of Ladakh receive less than 20 cm of annual rainfall.

- East to West decrease: In Northern India, rainfall decreases from east to west. Kolkata receives about 160 cm, while Jodhpur receives only about 36 cm.

3. Seasonal Variations:

- North India: Experiences four distinct seasons — hot summer, rainy season, cool autumn, and cold winter. Snowfall occurs in the Himalayan region.

- South India: Has a less pronounced seasonal variation. The temperature remains high throughout the year. The Tamil Nadu coast receives most of its rainfall in winter (October–December) from the north-east monsoon, unlike the rest of India.

- North-East India: Receives very heavy rainfall during the south-west monsoon. Cherrapunji and Mawsynram are among the wettest places on Earth.

4. Wind Variations:

- Loo: Hot, dry winds blow over the northern plains in summer.
- Kaal Baisakhi: Violent pre-monsoon thunderstorms occur in West Bengal and Assam in the evenings during summer.
- Mango showers: Pre-monsoon showers in Kerala and Karnataka help in the ripening of mangoes.

Conclusion: Despite these regional variations, the monsoon provides an overall climatic unity to the country by bringing rainfall to almost the entire country during the same season.

Given: We need to describe the cold weather season in India.

Answer:

Cold Weather Season (Winter Season)

Period: December to February

1. Temperature:
- The cold season sets in by November in northern India.
- The temperature decreases from south to north. In January (the coldest month), Chennai has a mean temperature of about $24–25°C$, while Delhi has about $14°C$, and Drass (Ladakh) can go as low as $-45°C$.
- Days are warm (due to sunshine) but nights are cold (due to clear skies allowing rapid radiation of heat). This gives a high diurnal range of temperature.
- Cold waves sweep across the northern plains, causing temperatures to drop sharply.

2. Pressure and Winds:
- High pressure develops over the northern plains due to the cold conditions.
- Winds blow outward from this high-pressure zone towards the sea.
- The north-east trade winds blow from the land towards the sea. Since they originate over land, they are dry and bring little rainfall to most parts of India.

3. Rainfall:
- Most of India is dry during this season.
- Western disturbances: Low-pressure systems originating over the Mediterranean Sea and moving eastward bring winter rainfall to the north-western plains (Punjab, Haryana, Delhi) and snowfall to the Himalayan region. This rainfall is very important for the Rabi crops (wheat, mustard, etc.).
- Tamil Nadu coast: Receives rainfall from the north-east monsoon (retreating monsoon) during October–December.

4. Sky Conditions:
- The sky is generally clear in most parts of India.
- Dense fog occurs in the northern plains, especially in December and January, disrupting transport.
- Frost is common in the northern plains and hilly areas.

5. Importance:
- The cool and dry weather is ideal for the cultivation of Rabi crops.
- The western disturbance rainfall is crucial for wheat cultivation in Punjab and Haryana.

Conclusion: The cold season in India is characterised by low temperatures (especially in the north), dry conditions over most of the country, occasional western disturbance rainfall in the north-west, and clear skies with fog in the northern plains.

Given: We need to describe the characteristics and effects of monsoon rainfall in India.

Answer:

Characteristics of Monsoon Rainfall:

1. Seasonal: Monsoon rainfall is seasonal, occurring mainly from June to September (south-west monsoon) and October–November (north-east monsoon in Tamil Nadu).

2. Uneven distribution: Rainfall is unevenly distributed across the country. Mawsynram receives over 1141 cm while the Thar Desert receives less than 20 cm annually.

3. Decreases from east to west in Northern India: As the Bay of Bengal branch moves westward, it progressively loses moisture, so rainfall decreases from east to west.

4. Orographic rainfall: The Western Ghats and the north-eastern hills receive very heavy rainfall on their windward sides due to orographic lifting of moisture-laden winds.

5. Uncertain and irregular: The onset, duration, and withdrawal of the monsoon are uncertain. Some years bring floods; others bring droughts. The monsoon can also have 'breaks' — dry spells within the rainy season.

6. Comes in bursts: The monsoon does not arrive gradually — it arrives suddenly with strong winds and heavy downpours. This is called the 'burst' of the monsoon.

7. Two branches: The south-west monsoon has two branches — the Arabian Sea branch (which brings rainfall to the western coast, Western Ghats, and parts of central India) and the Bay of Bengal branch (which brings rainfall to north-eastern India and the Ganga plains).

Effects of Monsoon Rainfall:

Positive Effects:

1. Agriculture: About 60% of India's agriculture depends on monsoon rainfall. It provides water for Kharif crops (rice, cotton, sugarcane, millets). The entire agricultural calendar revolves around the monsoon.

2. Water resources: Monsoon fills rivers, lakes, ponds, and groundwater reserves. It is the primary source of fresh water for India.

3. Hydroelectric power: Rivers swollen by monsoon water are used to generate hydroelectric power.

4. Forests and biodiversity: Monsoon rainfall supports India's rich forests and biodiversity. The tropical monsoon forests are a direct result of this rainfall pattern.

5. Relief from heat: After the scorching summer, the monsoon brings relief from the heat and refreshes the environment.

Negative Effects:

1. Floods: Excessive rainfall causes floods in river valleys (e.g., Brahmaputra valley, Bihar plains), destroying crops, property, and lives.

2. Droughts: Deficient or delayed monsoon causes droughts, leading to crop failure and water scarcity.

3. Soil erosion: Heavy monsoon rainfall causes soil erosion, especially on slopes and in areas with little vegetation cover.

4. Landslides: In hilly areas, heavy rainfall triggers landslides.

5. Disruption of transport: Heavy rainfall and floods disrupt road and rail transport.

Conclusion: The monsoon is the lifeline of India. Despite its uncertainties and occasional destructive effects, it is the most important climatic event in India, binding the entire country together through a shared experience of rain, agriculture, and culture.

Note: This question requires practical map work on an outline map of India. The following descriptions guide you on what to mark:

(i) Areas receiving rainfall over 400 cm (mark in dark blue/heavy shading):
- The north-eastern states — Meghalaya (especially Mawsynram and Cherrapunji), Assam, Arunachal Pradesh, Nagaland, Manipur, Mizoram, Tripura.
- The western coast — the Malabar coast (Kerala and coastal Karnataka), and parts of the Western Ghats.
- These areas receive very heavy rainfall due to orographic effect and their position on the windward side of hills.

(ii) Areas receiving less than 20 cm of rainfall (mark in yellow/light shading):
- Rajasthan (especially the Thar Desert — western Rajasthan).
- Parts of Gujarat (Kutch region).
- Ladakh (the cold desert in the rain shadow of the Himalayas and Karakoram).
- Parts of the Deccan Plateau in the rain shadow of the Western Ghats.

(iii) Direction of the south-west monsoon (draw arrows):
- Arabian Sea branch: Draw arrows from the Arabian Sea moving north-eastward towards the western coast of India (Kerala, Karnataka, Goa, Maharashtra). One branch moves northward along the western coast; another crosses the Western Ghats and moves over the Deccan Plateau and central India.
- Bay of Bengal branch: Draw arrows from the Bay of Bengal moving north-westward. One branch enters through the north-east (Brahmaputra valley) and moves westward along the Ganga plains. Another branch moves along the eastern coast.
- Both branches eventually merge over north-western India.

Instructions for map work: Use an outline map of India, mark the above regions with appropriate colours/shading, draw arrows to show wind direction, and add a legend/key to explain the markings.

Answer:

Thiruvananthapuram (Kerala): The south-west monsoon arrives at the Kerala coast by the 1st of June. The Arabian Sea branch of the monsoon is very active and vigorous when it first arrives. It strikes the Western Ghats with full force in June, causing very heavy rainfall. By July, the monsoon has spread over the entire country and its intensity over Kerala somewhat decreases. Hence, June is rainier than July in Thiruvananthapuram.

Shillong (Meghalaya): Shillong is located on the Meghalaya plateau, which is one of the first landmasses to receive the Bay of Bengal branch of the monsoon. The monsoon arrives here in early June with great vigour. The funnel-shaped topography of the Meghalaya hills (especially around Cherrapunji and Mawsynram) forces the winds to rise sharply, causing extremely heavy rainfall in June. By July, the monsoon has spread further and the intensity over Shillong may slightly decrease. Hence, June tends to be rainier than July in Shillong.

Answer:

The south-west monsoon arrives at the Kerala coast (Thiruvananthapuram) by the 1st of June and at Mumbai by about the 10th of June.

- In Thiruvananthapuram, the monsoon is most vigorous in June (when it first arrives). By July, its intensity over Kerala decreases as the monsoon has moved northward.

- In Mumbai, the monsoon arrives slightly later (mid-June) and reaches its peak intensity in July. The Arabian Sea branch of the monsoon strikes the Western Ghats near Mumbai with great force in July, causing very heavy rainfall.

Additionally, Mumbai's position on the western coast, directly facing the Arabian Sea, and the orientation of the Western Ghats near Mumbai, make July the rainiest month there. Hence, July is rainier in Mumbai than in Thiruvananthapuram.

Answer:

The south-west monsoons are less rainy in Chennai due to the following reasons:

1. Rain shadow area: Chennai (on the Coromandel coast, eastern side) lies in the rain shadow area of the Western Ghats. The Arabian Sea branch of the south-west monsoon sheds most of its moisture on the windward (western) side of the Western Ghats. By the time it crosses the Ghats and reaches Chennai, it has very little moisture left.

2. Bay of Bengal branch moves parallel: The Bay of Bengal branch of the south-west monsoon moves roughly parallel to the Tamil Nadu coast (in a north-westward direction). It does not strike the coast perpendicularly and hence does not cause significant orographic rainfall on the Tamil Nadu coast.

3. Compensation in winter: Chennai makes up for this deficiency by receiving rainfall from the north-east monsoon (retreating monsoon) during October–December, when moisture-laden north-east winds blow from the Bay of Bengal towards the Tamil Nadu coast.

Answer:

Shillong receives much more rainfall than Kolkata due to the following reasons:

1. Topography: Shillong is located on the Meghalaya plateau (altitude about 1496 m). The Bay of Bengal branch of the south-west monsoon, after entering through the Bay of Bengal, is funnelled into the narrow gap between the Meghalaya hills and the Himalayas. The hills force the moisture-laden winds to rise sharply, causing very heavy orographic rainfall.

2. Funnel effect: The shape of the Meghalaya hills (especially the Khasi Hills) acts like a funnel, concentrating the moisture-laden winds and forcing them upward, resulting in extremely heavy rainfall.

3. Kolkata is on the plains: Kolkata is located on the flat Ganga delta. There are no hills to force the winds to rise. The monsoon passes over Kolkata without being forced to rise, so it receives much less rainfall than Shillong.

4. Distance from the sea: While both are influenced by the Bay of Bengal branch, Shillong's topography amplifies the rainfall effect much more than Kolkata's flat terrain.

Answer:

Shillong is rainier in June than July: The Bay of Bengal branch of the south-west monsoon arrives at the Meghalaya hills in early June with full vigour. The hills force the winds to rise immediately, causing very heavy rainfall in June. By July, the monsoon has spread over the entire country and its intensity over Shillong somewhat decreases.

Kolkata is rainier in July than June: The south-west monsoon arrives at Kolkata slightly later than at Shillong (Kolkata is further west and south of the Meghalaya hills). The monsoon builds up gradually over Kolkata. By July, the monsoon is fully established over the entire Ganga delta region and reaches its peak intensity over Kolkata. Hence, July receives more rainfall than June in Kolkata.

In essence, the monsoon arrives earlier and with greater initial force at Shillong (due to topography), making June rainier there. At Kolkata, the monsoon takes time to build up to its full intensity, making July the rainiest month.

Answer:

Delhi receives more rainfall than Jodhpur due to the following reasons:

1. Bay of Bengal branch: The Bay of Bengal branch of the south-west monsoon moves westward along the Ganga plains. Delhi lies in the path of this branch and receives a significant amount of rainfall from it. Jodhpur, being further west and south-west, is beyond the effective reach of this branch.

2. Distance from moisture source: Delhi is closer to the Bay of Bengal branch's path than Jodhpur. As the monsoon moves westward, it progressively loses moisture. By the time it reaches Jodhpur, it has very little moisture left.

3. Aravalli Mountains: The Aravalli range runs parallel to the direction of the Arabian Sea branch of the monsoon near Jodhpur. It does not act as a barrier to force the winds to rise and precipitate. Hence, the Arabian Sea branch passes over Jodhpur without causing significant rainfall.

4. Thar Desert influence: Jodhpur is located near the Thar Desert. The hot, dry desert conditions further reduce the possibility of rainfall.

As a result, Delhi receives about 56 cm of annual rainfall while Jodhpur receives only about 36 cm.

Answer:

Thiruvananthapuram has an equable (moderate) climate due to the following reasons:

1. Coastal location: Thiruvananthapuram is located on the south-western coast of India, very close to the Arabian Sea. The sea has a moderating influence on temperature — it prevents extreme heat in summer and extreme cold in winter.

2. Low latitude: Being located near the equator (about 8°N latitude), the sun's rays are almost vertical throughout the year. This means there is little seasonal variation in the amount of solar radiation received, keeping temperatures fairly uniform throughout the year.

3. Sea breeze: The sea breeze from the Arabian Sea keeps the temperature moderate during the day, while the land breeze at night prevents temperatures from falling too low.

4. High humidity: The proximity to the sea keeps the humidity high, which also moderates temperature extremes.

As a result, Thiruvananthapuram has a small annual range of temperature (about $3–4°C$) and a small diurnal range, making it an equable climate.

Answer:

Chennai receives most of its rainfall during October–December (after the south-west monsoon has retreated from most of India) due to the following reasons:

1. Rain shadow during south-west monsoon: During the south-west monsoon (June–September), Chennai lies in the rain shadow area of the Western Ghats. The Arabian Sea branch loses its moisture on the western side of the Ghats. The Bay of Bengal branch moves parallel to the Tamil Nadu coast and does not cause significant rainfall.

2. North-east monsoon: After the south-west monsoon retreats (by October), the north-east monsoon (retreating monsoon) sets in. The north-east trade winds blow from the land towards the sea. As they pass over the Bay of Bengal, they pick up moisture and bring rainfall to the Tamil Nadu coast (including Chennai) during October–December.

3. Cyclones: The Bay of Bengal is prone to cyclones during October–November, which also bring heavy rainfall to Chennai and the Tamil Nadu coast.

Thus, while the rest of India receives most of its rainfall during June–September, Chennai receives most of its rainfall during October–December — after the fury of the south-west monsoon is over in most parts of the country.

Answer:

Jodhpur has a hot desert type of climate due to the following reasons:

1. Location in the Thar Desert: Jodhpur is located in the Thar Desert of Rajasthan, which is one of the world's major hot deserts.

2. Very low rainfall: Jodhpur receives only about 36 cm of annual rainfall. The Aravalli Mountains run parallel to the direction of the Arabian Sea branch of the monsoon and do not force the winds to rise and precipitate. The Bay of Bengal branch loses most of its moisture before reaching Jodhpur.

3. Sandy soil: The sandy soil heats up rapidly during the day and cools rapidly at night, causing extreme temperatures.

4. Sparse vegetation: The lack of vegetation means there is no shade or moisture retention, leading to high temperatures and rapid evaporation.

5. High temperatures: Jodhpur experiences very high temperatures in summer (above $40°C$) and relatively cold winters, with a very high diurnal range of temperature.

6. Dry winds: Hot, dry winds (Loo) blow over the region in summer, further desiccating the landscape.

All these factors combine to give Jodhpur a hot desert type of climate.

Answer:

Leh (Ladakh) has moderate precipitation almost throughout the year due to the following reasons:

1. Rain shadow of the Himalayas: Leh is located in the cold desert of Ladakh, which lies in the rain shadow of the Great Himalayas. The south-west monsoon cannot penetrate into Ladakh because the Himalayas and the Karakoram range block the moisture-laden winds. Hence, the south-west monsoon brings very little rainfall to Leh.

2. Western disturbances in winter: During winter, western disturbances (low-pressure systems from the Mediterranean) bring snowfall and some precipitation to Ladakh. This provides some moisture during the winter months.

3. High altitude: Leh is at a very high altitude (about 3500 m). At this altitude, even small amounts of moisture can precipitate as snow. The precipitation is spread over many months in the form of snowfall.

4. Cold desert conditions: The overall precipitation is very low (less than 20 cm annually), but because it is spread across many months (both summer monsoon remnants and winter western disturbances), it appears as moderate precipitation throughout the year rather than being concentrated in one season.

Thus, Leh receives small amounts of precipitation spread across the year from different sources.

Answer:

Delhi and Jodhpur (rain confined to ~3 months):
- Both Delhi and Jodhpur receive rainfall almost entirely from the south-west monsoon (July–September), which lasts only about 3 months in these regions.
- They do not receive significant rainfall from the north-east monsoon (which affects only the Tamil Nadu coast).
- Western disturbances bring some winter rainfall to Delhi but not to Jodhpur.
- Hence, rainfall is concentrated in about 3 months.

Thiruvananthapuram (rain for ~9 months):
- Thiruvananthapuram receives rainfall from multiple sources over a longer period:
- Pre-monsoon showers (April–May): Mango showers and thunderstorms.
- South-west monsoon (June–September): Heavy rainfall from the Arabian Sea branch.
- North-east monsoon (October–December): Rainfall from the retreating monsoon.
- This gives Thiruvananthapuram about 9 months of rainfall.

Shillong (rain for ~9 months):
- Shillong receives rainfall from:
- Pre-monsoon thunderstorms (April–May).
- South-west monsoon (June–September): Very heavy rainfall due to orographic effect.
- Post-monsoon (October–November): Some rainfall continues due to the Bay of Bengal branch.
- The topography of the Meghalaya hills ensures that moisture-laden winds cause rainfall for a longer period.

Conclusion: The difference is due to the geographical location (latitude, proximity to the sea), topography, and exposure to multiple rainfall-bearing systems in Thiruvananthapuram and Shillong, compared to Delhi and Jodhpur which depend almost entirely on the south-west monsoon for a short period.