Module 54. Climatology and Weather Patterns in India
India’s climatology represents a complex interplay of geographical location, topography, monsoonal dynamics, and global atmospheric circulation systems. Stretching from the Himalayan highlands in the north to the tropical coasts in the south, the country experiences diverse climatic conditions ranging from arid deserts to humid rainforests. Understanding India’s weather patterns is crucial for agriculture, water resource management, and disaster preparedness.
Geographical and Climatic Background
India lies entirely in the northern hemisphere between latitudes 8°4′N and 37°6′N and longitudes 68°7′E and 97°25′E. The Tropic of Cancer passes almost through its middle, dividing the country into tropical and subtropical zones. This geographical positioning, combined with its peninsular shape, results in varied climatic conditions across different regions.
According to the Köppen climate classification, India features several types of climates:
- Tropical wet (monsoon) climate in the western coast, Assam, and parts of the north-east.
- Tropical dry (steppe and desert) climate in Rajasthan, Gujarat, and interior Deccan plateau.
- Subtropical humid climate in northern plains and foothills of the Himalayas.
- Mountain climate in the Himalayan region.
The Himalayas act as a climatic divide, preventing the cold Siberian winds from entering India and forcing the south-west monsoon winds to rise, resulting in heavy rainfall on the windward side. The Thar Desert in the northwest influences the formation and intensity of the monsoon.
Major Climatic Seasons
The Indian Meteorological Department (IMD) classifies the Indian year into four distinct seasons based on weather patterns and temperature variations:
- Winter Season (December to February) – Characterised by dry and cool conditions. Northern India experiences temperatures below 10°C in the plains, while southern India remains relatively warmer. Western disturbances originating from the Mediterranean region bring occasional rainfall and snowfall to north-western India.
- Summer Season (March to May) – Marked by rising temperatures, reaching up to 45°C in northern plains and central regions. The pre-monsoon months witness the development of local winds such as Loo in the north and Kalbaisakhi thunderstorms in eastern India.
- South-west Monsoon Season (June to September) – The most significant season, accounting for nearly 75% of the annual rainfall. The monsoon enters India through the Kerala coast around 1 June and gradually covers the entire country by mid-July. Two branches – the Arabian Sea and the Bay of Bengal – deliver rainfall to different regions.
- Retreating or North-east Monsoon Season (October to November) – The withdrawal of the south-west monsoon marks this period. The north-east monsoon brings rainfall primarily to Tamil Nadu, coastal Andhra Pradesh, and parts of the eastern coast.
The Monsoon System
The monsoon is the defining element of India’s climate. It is a large-scale seasonal reversal of winds due to differential heating of land and sea. During summer, the landmass of the Indian subcontinent heats up faster than the surrounding ocean, creating a low-pressure zone that attracts moisture-laden winds from the Indian Ocean. Conversely, in winter, high pressure over the land drives dry winds toward the sea.
Key features of the Indian monsoon include:
- Onset and withdrawal: The monsoon typically sets in over Kerala in early June and retreats by early October.
- Variability: The amount and distribution of rainfall vary widely from year to year, influencing agriculture and water availability.
- Breaks and active spells: Periods of heavy rainfall alternate with dry spells, affecting crop productivity.
- Regional variations: Western Ghats, northeastern states, and coastal areas receive over 200 cm of rainfall annually, while western Rajasthan receives less than 20 cm.
Regional Weather Patterns
The climatic diversity of India manifests through distinct regional weather patterns:
- Northern Plains: Experience extreme temperature variations, from cold winters to scorching summers, with moderate monsoonal rainfall.
- Western Desert (Thar): Characterised by arid conditions, sparse rainfall, and high diurnal temperature range.
- Peninsular India: Enjoys a moderate climate with less variation in temperature due to maritime influence.
- Himalayan Region: Exhibits mountain climate with altitude-dependent temperature and precipitation; snow and glaciers dominate the higher reaches.
- Coastal Regions: Maintain equable temperatures with high humidity and frequent cyclonic activity, especially along the Bay of Bengal.
Cyclones and Extreme Weather Events
Cyclonic disturbances significantly influence India’s weather, particularly along its eastern and western coasts. The Bay of Bengal witnesses more cyclonic formations due to warmer sea-surface temperatures and favourable wind patterns. These cyclones, especially during the pre- and post-monsoon periods, can cause heavy rainfall, storm surges, and extensive damage to infrastructure and agriculture.
In addition to cyclones, India experiences heatwaves, cold waves, fog, and droughts. The frequency and intensity of such extreme events have shown increasing trends due to climate change and urbanisation. The IMD and the National Disaster Management Authority (NDMA) have developed early warning systems and mitigation strategies to reduce their impact.
Influence of Global Phenomena
India’s climate is also influenced by several global climatic phenomena:
- El Niño and La Niña: These Pacific Ocean events affect monsoon behaviour; El Niño often leads to drought-like conditions, while La Niña tends to strengthen monsoonal rainfall.
- Indian Ocean Dipole (IOD): The difference in sea-surface temperature between the western and eastern Indian Ocean can modulate the monsoon’s strength.
- Western Disturbances: Upper-level westerly winds originating in the Mediterranean bring winter rainfall to northern India.
Impact on Agriculture and Economy
Agriculture in India is largely dependent on monsoonal rainfall, with about two-thirds of the cultivated area relying on rain-fed systems. A good monsoon ensures food security, while a deficient one can lead to drought, crop failure, and economic stress. The timing and distribution of rainfall are often more critical than the total amount received.
The monsoon also influences hydroelectric power generation, river flow patterns, and groundwater recharge. Conversely, excessive rainfall can lead to floods, soil erosion, and landslides, particularly in hilly and coastal areas.
Climate Change and Emerging Challenges
Recent trends indicate changes in India’s climatic patterns, including erratic monsoons, rising temperatures, and shifting rainfall zones. The frequency of intense rainfall events has increased, while moderate rainfall days have declined. The Himalayan glaciers are retreating, threatening long-term water availability in northern river systems.
The Government of India, through initiatives such as the National Action Plan on Climate Change (NAPCC) and State Action Plans on Climate Change (SAPCCs), has sought to build resilience through adaptation and mitigation strategies. Focus areas include sustainable agriculture, renewable energy, afforestation, and early warning systems for extreme weather events.