Climate and Vegetation in India

Learning Outcomes:

1. Understand the difference between weather and climate.
2. Identify the factors affecting India’s climate.
3. Learn about the monsoon mechanism in India.
4. Recognize the distribution of natural vegetation and forest types.

Weather and Climate

India’s climate is diverse due to spatial and temporal variations. The weather represents the short-term atmospheric conditions like temperature, pressure, wind, and precipitation. In contrast, climate refers to the average weather over a longer period, often over decades. India’s climate is monsoonal, experiencing distinct seasonal variations.

Important Note: The monsoon climate unites India with Southeast Asia, but there are noticeable regional variations. For instance, Kerala and Tamil Nadu’s climates are significantly different from Uttar Pradesh and Bihar, despite sharing a monsoon climate.

Seasonal and Regional Variations in Temperature

1. Summer Extremes: In western Rajasthan, temperatures can reach 55°C in summer, while Leh experiences temperatures as low as -45°C in winter. Churu records highs of 50°C, while Tawang may be as low as 19°C on the same day.
2. Winter Extremes: Drass (Ladakh) experiences -45°C on a December night, while Thiruvananthapuram and Chennai may register 20°C or higher.
3. Diurnal Temperature Differences: In Kerala and the Andaman Islands, day-night temperature differences are minimal (7-8°C). In contrast, Thar Desert shows a dramatic drop from 50°C during the day to as low as 15°C at night.

Regional Precipitation Variations

1. Snow and Rain: Snowfall occurs only in the Himalayas, while the rest of the country experiences rain.
2. Annual Precipitation: Cherrapunji and Mawsynram receive over 1,080 cm of rainfall annually, while Jaisalmer rarely gets more than 9 cm.
3. Rainfall Distribution: The Ganga delta and Odisha experience strong rainstorms in July and August, while the Coromandel coast remains dry. Coastal Tamil Nadu experiences rains at the beginning of the winter season.

Factors Affecting India’s Climate

India’s climate is shaped by various geographical factors:

1. Latitude: India’s northern region lies in the sub-tropical and temperate zone, while the southern part is in the tropical zone, leading to higher temperatures in the south.
2. Himalayan Barrier: The Himalayas act as a shield, blocking cold winds from Central Asia and trapping monsoon winds, forcing them to shed moisture over India.
3. Land and Water Distribution: The differential heating of land and sea creates varying air pressure zones, leading to the reversal of monsoon winds.
4. Distance from the Sea: Coastal regions like Mumbai enjoy an equable climate, while inland areas like Delhi and Kanpur experience extremes.
5. Altitude: Higher elevations, such as Darjeeling, are cooler compared to plains like Agra, even though they share the same latitude.
6. Relief: Physiography influences wind and rainfall. The windward sides of the Western Ghats and Assam receive significant rainfall, while the southern plateau remains dry.

The Nature of the Indian Monsoon

The Indian monsoon is complex and critical to the country’s climate. Despite extensive research, it remains a partially understood phenomenon. Understanding the onset and break of the monsoon provides crucial insights into its behavior.

Onset of the Monsoon

1. Differential Heating: During summer, the large landmass north of the Indian Ocean heats up, creating low-pressure areas. This draws in winds from the high-pressure Indian Ocean, setting the stage for monsoon winds.
2. Inter-Tropical Convergence Zone (ITCZ): The ITCZ shifts northward, drawing in southeast trade winds across the equator, which are deflected to become the southwest monsoon.
3. Entry into India: The southwest monsoon reaches the Kerala coast by June 1 and moves across India, engulfing the entire subcontinent by mid-July.

Break in the Monsoon

During the rainy season, there may be periods of no rain lasting for days or weeks, known as a monsoon break. These breaks occur due to the following:

1. Northern India: Breaks happen when rain-bearing storms are less frequent along the monsoon trough.
2. West Coast: Dry spells occur when winds blow parallel to the coast.

Rhythm of the Seasons

India’s climate is characterized by four primary seasons:

1. Cold Weather Season (Winter): Starting in mid-November, with December and January being the coldest months. Northern regions experience temperatures below 21°C, while some areas face freezing conditions.
2. Hot Weather Season (Summer): Starting in March, temperatures rise in northern India. By May, northwestern India experiences temperatures as high as 48°C.
3. Southwest Monsoon Season (Rainy Season): The monsoon brings rains from June to September. The Arabian Sea and Bay of Bengal branches of the monsoon winds cause heavy rainfall across India.
4. Retreating Monsoon Season: In October and November, as the monsoon retreats, temperatures drop, and the weather becomes oppressive, commonly referred to as October heat.

Traditional Indian Seasons

In Indian tradition, a year is divided into six two-month seasons:

Distribution of Rainfall

India experiences considerable rainfall variation across regions:

1. High Rainfall Areas: Western Ghats and northeast India, particularly the Khasi Hills, receive over 200 cm of rainfall annually.
2. Medium Rainfall Areas: Eastern India, parts of Gujarat, and Tamil Nadu receive 100-200 cm.
3. Low Rainfall Areas: Western Uttar Pradesh, Delhi, Haryana, and parts of Rajasthan receive 50-100 cm.
4. Inadequate Rainfall: Parts of Andhra Pradesh, Karnataka, Maharashtra, and Rajasthan receive less than 50 cm of rainfall.

The Impact of Monsoons on Indian Life

1. Agriculture: The monsoon is crucial for agriculture, as 64% of India’s population depends on it. Timely rainfall is essential for the agricultural cycle.
2. Regional Variations: The variability of rainfall affects crop variety and can lead to droughts or floods.
3. Economic Impact: Properly timed rainfall leads to agricultural prosperity, while failure causes severe economic damage.
4. Soil Erosion: Sudden bursts of monsoon rains often lead to soil erosion.

Global Warming and Climate Change

Global warming is a pressing issue influenced by natural and human factors. Carbon dioxide, methane, and other greenhouse gases have significantly contributed to warming. This phenomenon has multiple consequences:

1. Rising Sea Levels: Due to melting ice caps, the sea level could rise by 48 cm by the end of the century, increasing flooding risk.
2. Agricultural Shifts: Changes in climate will shift agricultural patterns and affect food production.
3. Insect-borne Diseases: Warmer climates may promote diseases like malaria.

Important Note: The effects of global warming are particularly concerning for India’s coastal regions, which could face significant flooding.

The Southwest Monsoon Season

The southwest monsoon is the lifeline for India’s agriculture, bringing rain to most parts of the country. However, not all regions benefit equally, and some areas remain rain-shadow regions due to the obstruction of the Western Ghats.

Monsoon Winds of the Arabian Sea

1. Western Ghats: Winds rising along the Western Ghats bring heavy rainfall (250-400 cm), but the leeward side remains dry.
2. Central India: Winds follow the Narmada and Tapi valleys, bringing rain to central regions.
3. Western Rajasthan: The third branch of the Arabian Sea monsoon brings little rain to this region.

Monsoon Winds of the Bay of Bengal

The **Bay

of Bengal branch** brings heavy rains to West Bengal and Bangladesh before splitting into two. One branch moves westward, while the other heads toward the Brahmaputra valley.

Important Note: Tamil Nadu remains dry during the monsoon because it lies in the rain-shadow area.

MCQ: What causes rainfall on Tamil Nadu’s coastal areas at the beginning of winter?
Answer: North-Eastern Monsoon