Climate of India

Climate refers to the overall weather patterns and fluctuations that occur over a large area for an extended period, typically over decades or longer. It differs from weather, which is the state of the atmosphere in a specific location over a short period. The key elements of weather and climate include temperature, air pressure, wind, humidity, and precipitation. Weather conditions can change rapidly within a day, but over a period of weeks or months, specific trends emerge—such as whether it is hot or cold, windy or calm, or rainy or dry.

India’s monsoon climate, primarily found in southern and southeastern Asia, exhibits regional variations, ranging from extreme cold in the northern Himalayas to hot desert in Rajasthan.

Factors Influencing Climate in India:

Several geographical and meteorological factors influence India’s climate, resulting in regional differences in temperature, winds, and rainfall:

Latitude:

• Solar energy received varies by region due to Earth’s curvature, causing significant temperature variations.
• Higher altitudes result in cooler temperatures due to decreased atmospheric pressure.
• Mountains with thinner air are cooler than plains, resulting in a hot tropical climate.

Relief:

• Physical features of land like mountains and plateaus significantly affect weather conditions.
• Relief influences air pressure, wind patterns, temperature, wind speed, and rainfall distribution.

Distance from the Sea:

• Coastal regions experience mild climates with minimal temperature variation.
• Areas like Chennai and the Konkan Coast experience relatively stable temperatures.
• Inland areas experience continental-type climates with larger temperature variations.

Winds and Rainfall:

• Winds and type and amount of rainfall can vary significantly across India.
• Rainfall distribution is affected by mountain presence and wind direction.
• Most rainfall occurs during the south-west monsoon from June to September.

Air Pressure and Winds:

• The coasts of India, including areas like the Sundarbans and the Andaman and Nicobar Islands, are home to mangrove forests, which can survive in both fresh and saltwater.

Ocean Currents:

• Warm and cold ocean currents affect the climate of India’s coastal regions.

Seasons and Their Characteristics in India:

There are significant seasonal variations in India’s monsoon climate. The weather changes drastically from one season to another, and these shifts are most noticeable in the central regions, especially in the northern and northwestern parts of India. Coastal areas experience less temperature variation, while rainfall follows a predictable cycle. Indian meteorologists identify four primary seasons:

1. The Cold Weather Season (Winter):
   • Winter starts in mid-November and lasts until February.
   • Coldest months are December and January.
   • Southern parts like coastal areas have milder winters.
   • Northern plains and Himalayan regions experience colder temperatures.
   • Higher altitudes may see snowfall.
   • Northeast trade winds bring dry, cool air, contributing to Northeast Monsoon winter rainfall.
2. Cold Waves:
   • Fall below 6°C between November and April.
   • Most affected regions: Jammu & Kashmir, Punjab, Uttar Pradesh, Rajasthan, Madhya Pradesh.
   • Frequency decreases as southward movement occurs.
3. The Hot Weather Season (Summer):
   • Temperatures rise in February-March, especially in the south.
   • By May, temperatures soar to 33°C or higher, especially south of Vindhyas.
   • Rise causes a drop in air pressure, forming a low-pressure  area from Thar Desert to Chotanagpur Plateau.
   • Hot, dry winds, known as loo, blow across Ganga plains during afternoons and may continue until night.
4. Hot Waves: Between March and July, parts of India experience extreme heat waves. The regions most affected include the northwestern plains, Uttar Pradesh, and Rajasthan, while southern regions like Kerala and Tamil Nadu remain relatively unaffected. Heat waves are common in northwestern India, occurring at least once a year.
   

India’s climate is highly diverse, influenced by various geographical and meteorological factors. Understanding these variations helps in the study of regional weather patterns and the impact they have on agriculture, daily life, and ecosystems across the country.

The Season of Advancing Monsoon:

In April and May, the intense heat of the land in North-West India creates a low-pressure area. This is due to the land warming up significantly, causing the air above it to rise, thereby reducing air pressure in the region. Meanwhile, the equatorial low-pressure system grows stronger, and the South-East trade winds—originating from the warm subtropical portions of the Southern Oceans—begin to blow toward this low-pressure area. By early June, these winds, moving over the Indian Ocean, cross the equator. As they do, they are deflected to the right in the Northern Hemisphere, transforming into the South-West Monsoon.

The advancing monsoon season is marked by humidity-laden winds that bring rainfall as they pass over the warm equatorial currents. These winds divide as they approach the Indian Peninsula, forming two branches: the Arabian Sea branch and the Bay of Bengal branch. By early June, these two branches reach India, signaling the onset of the monsoon. Over the next four to five weeks, the monsoon gradually spreads across the country, bringing rains with it. The winds carry substantial moisture, which results in rainfall, particularly as they pass over the warm ocean currents.

The Season of Retreating Monsoon:

In October and November, with the apparent southward movement of the sun, the monsoon trough weakens, and the region starts experiencing a shift towards high-pressure conditions. As a result, the South-West Monsoon begins to retreat. This phase is characterized by the gradual withdrawal of the monsoon winds, which weakens their intensity and leads to a clear sky and a rise in temperatures.

During this time, although daytime temperatures remain high, nights become cooler and more pleasant. The air still holds some moisture, leaving the land relatively moist, but the increasing humidity and high temperatures during the day can make the weather feel oppressive. This phenomenon is referred to as October Heat. By the second half of October, the mercury begins to fall rapidly, especially in Northern India.

By early November, the low-pressure area shifts from north-western India to the Bay of Bengal. This shift in pressure leads to the formation of cyclonic depressions that originate in the Andaman Sea and move towards the east coast of India, bringing heavy rainfall, particularly in Odisha, Andhra Pradesh, and Tamil Nadu. These coastal areas are often affected by thunderstorms, which contribute to the rainfall during this period.

Climatic Divisions of India:

The climate across India is highly diverse and varies significantly from one region to another. These variations, including differences in monsoonal climates, can be classified based on various factors such as temperature, rainfall, and seasonal patterns.

Köppen’s Climate Classification System: Köppen’s scheme classifies climates based on monthly temperature and precipitation values. The five primary climatic types identified by Köppen are:

1. Tropical Humid Climates: In these regions, the average monthly temperature remains above 18°C year-round.
2. Dry Climates: These areas experience high temperatures with limited rainfall, leading to semi-arid or arid conditions.
3. Warm Climates: In these regions, the mean temperature ranges from 18°C to 3°C during the coldest months.
4. Snow Climates: These climates are characterized by a mean temperature of over 10°C during the warmest month and below 3°C during the coldest.
5. Ice Climates: In these areas, the warmest month has a mean temperature of under 10°C.

Thornthwaite’s Water Balance Classification: Thornthwaite’s climatic classification is based on the concept of water balance, which is the relationship between rainfall and the water demand from evaporation and plant transpiration. Areas where rainfall exceeds the water demand have a humid climate, while regions where rainfall is insufficient to meet evaporation needs are classified as dry.

This classification accounts for seasonal changes in both rainfall and water demand, using formulas to calculate water surplus and deficit over time.

Stamp’s Climate Classification: Based on the 18°C isotherm for January, Stamp’s scheme divides India into two major climatic regions:

1. Subtropical India: This region includes areas like the Himalayan regions, northwestern plateau, dry plains of the northwest, and medium rainfall areas such as Punjab, Uttar Pradesh, and parts of Haryana.
2. Tropical India: This region is further divided based on rainfall patterns, such as:
   • Very Heavy Rainfall regions like Assam and Meghalaya.
   • Heavy Rainfall areas, including West Bengal, Odisha, and parts of Andhra Pradesh.
   • Medium Rainfall regions such as the Konkan Coast, Malabar Coast, and parts of Tamil Nadu.

RL Singh’s Climate Classification: In 1971, Professor RL Singh introduced a modified climate classification system based on annual rainfall and temperature regimes. This classification is also influenced by variations in monthly temperatures, particularly in July and January. Singh divided India into ten climatic groups, including:

• Sub-Humid Transitional Regions: Found in areas like the middle Ganga plain and Coromandel coast.
• Semi-Arid Tropical Regions: Found in areas like central Gujarat and Maharashtra.
• Arid Regions: Found in regions such as Kachchh and parts of South-Western Haryana.
• West Himalayas: Including Jammu & Kashmir, Himachal Pradesh, and Uttarakhand with their steep terrain.

This system allows for a more nuanced understanding of India’s diverse climatic regions, incorporating both precipitation and temperature variations.

India’s climate, influenced by various geographical and meteorological factors, is divided into multiple climatic zones. These zones differ significantly in terms of temperature, rainfall, and other climatic factors, contributing to the country’s rich diversity of ecosystems and weather patterns.