Chapter 3 Climates Of India

Weather, Seasons And The Climate

While often used interchangeably, weather and climate refer to different concepts. Weather describes the state of the Earth's atmosphere at a specific time and place. It refers to short-term conditions like temperature, precipitation, wind, and humidity experienced hourly or daily. Weather is constantly changing.

Climate, on the other hand, represents the long-term pattern of weather that a particular area or region experiences over an extended period, typically several decades (30 years or more). It describes the average weather conditions, seasonal variations, and frequency of extreme events for a region.

Seasons are periods of the year characterized by specific weather conditions that repeat annually. Seasons occur as the Earth revolves around the Sun, causing different parts of the planet to receive varying amounts of solar energy throughout the year. Common seasons in many parts of the world include spring, summer, autumn, and winter.

Seasons are related to both weather and climate. The daily weather changes within a season, but the overall characteristics of weather (e.g., hot and dry, humid and rainy) are typical for that season in a particular climate. The pattern of seasons is a defining feature of a region's climate.

Traditionally, in many parts of India, the year is divided into six seasons, known as Ritus:

• Vasanta: Spring
• Grishma: Summer
• Varsha: Rainy season (Monsoon)
• Sharad: Autumn
• Hemanta: Pre-winter
• Shishir: Winter

These traditional seasons are often linked to specific cultural practices, rituals, and festivals like Vasanta Panchami or Sharad Purnima. Life, including human activities (like farming, clothing choices), plant growth (blooming, shedding leaves), and animal behaviour (developing fur), is often in rhythm with these seasonal changes.

While climate has historically been stable over long periods, recent decades have seen significant changes in global and regional climates, largely attributed to human activities.

Types Of Climates In India

India's vast geographical diversity contributes to a wide range of climatic conditions across the country. Different regions experience distinct climate types:

• Alpine Climate: Found in the high Himalayan mountains (e.g., Himadri range), characterized by very cold, snowy winters and cool summers. Requires heavy clothing.
• Temperate Climate: Present in lower Himalayan regions (e.g., Himachal range) and other hilly areas. Features moderately cold winters and not excessively hot summers. Many popular 'hill stations' with pleasant climates are located here.
• Subtropical Climate: Common in the Northern Plains, experiencing very hot summers and cold winters. This climate is highly favourable for growing crops like wheat.
• Arid Climate: Found in the Thar Desert region in the west, characterized by extreme heat during the day, cold nights, and very scarce rainfall. Requires unique adaptations for water conservation.
• Tropical Wet Climate: Experienced along the western coastal strip, receiving heavy rainfall, particularly during the monsoon season. This climate supports the cultivation of rice and spices.
• Semi-arid Climate: Found in the central Deccan Plateau, featuring hot summers, mild winters, and moderate rainfall concentrated during the rainy season.
• Tropical Climate: Prevalent in Eastern India and the southern peninsula. Characterized by mild winters and distinct wet and dry periods influenced by monsoon winds.

Understanding the factors that influence these different climate types helps explain India's varied weather patterns and seasonal cycles.

Factors Determining The Climate

Several factors, operating at global, regional, and local scales, interact to determine the climate of any particular place. Key factors include:

Latitude

Latitude is the distance of a place from the Equator, measured in degrees. Latitude significantly affects temperature because it determines the angle at which sunlight strikes the Earth's surface.

Places near the Equator (low latitudes) receive the sun's rays almost perpendicularly. This concentrates the sun's energy over a smaller area, resulting in higher temperatures. As latitude increases (moving towards the poles), the sun's rays become more inclined or oblique. This spreads the solar energy over a larger area and requires the rays to pass through a greater thickness of the atmosphere, reducing the heat reaching the surface. Consequently, temperatures generally decrease as latitude increases, leading to warm/hot climates near the Equator, temperate climates in mid-latitudes, and cold/frigid climates near the poles.

In India, places closer to the Equator, like Kanyakumari and the Nicobar Islands (around 8°N latitude), experience warm or hot weather year-round, while locations further north in the Himalayas, like Srinagar (around 34°N latitude), have much colder temperatures.

Altitude

Altitude refers to the height of a place above sea level. As altitude increases, temperature generally decreases. This is why places at higher elevations, like hill stations in India, are cooler than the plains below, even at the same latitude.

Reasons for temperature decrease with altitude:

1. Decreasing Air Density: Atmospheric pressure and air density decrease with altitude. Less dense air holds less heat.
2. Distance from Earth's Surface: The Earth's surface is primarily heated by the sun, and this heat is then transferred to the air above. Air further away from the heated surface is generally cooler.

Mountains like the Himalayas are so high that temperatures remain below freezing point, resulting in permanent snow cover on many peaks.

Proximity To The Sea

The distance of a place from the sea affects its climate, particularly temperature variations. Coastal areas generally experience more moderate temperatures, with less extreme differences between summer and winter, compared to places located far inland at the same latitude.

The sea acts as a temperature moderator because water heats up and cools down more slowly than land. During summer, the sea remains cooler than the land, and sea breezes help cool coastal areas. In winter, the sea retains heat longer than the land, warming the coastal regions. This results in a smaller temperature range in coastal areas.

For example, Mumbai, a coastal city, has a much smaller temperature range between summer and winter than Nagpur, an inland city at a similar latitude. Mumbai's temperatures are moderated by the Arabian Sea, while Nagpur experiences more extreme seasonal temperatures.

Winds

Winds are air movements that can transport air masses with different characteristics across regions. Winds can carry warm or cold air, affecting the temperature of the areas they blow over. For instance, hot, dry winds blowing from desert regions can cause heatwaves, while cold winds from snowy mountains can lead to cold waves.

Winds also influence humidity and precipitation by carrying moisture. Winds blowing from over the sea are often moisture-laden and can bring rainfall to the land, while winds blowing from over landmasses are typically dry.

The seasonal reversal of winds, known as monsoons, is a critical climatic phenomenon in India, bringing significant rainfall.

Topography

The topography, or the physical surface features of an area (mountains, valleys, plains, etc.), significantly influences local and regional climates. Mountains can act as barriers to wind and precipitation. For example, the Himalayas partially block cold winds from Central Asia from entering the Indian subcontinent.

Mountain ranges like the Western Ghats can influence rainfall patterns; their windward side (facing the moist winds) receives heavy rainfall, while the leeward side (away from the winds) experiences a rain shadow effect, receiving much less rain.

The shape of the land can also affect temperature and wind flow. Valleys might trap cold air, while open plains might be more exposed to winds.

The combined effect of latitude, altitude, proximity to the sea, winds, and topography determines the specific climate patterns, including temperature range, precipitation (rain, snow, fog, mist), and wind conditions, that characterize a region over the long term.

Within a broader climate region, localized areas can have their own distinct climate patterns called microclimates. These are variations in temperature, humidity, etc., in a small geographical area, such as a valley, a forest, or even urban areas (like 'urban heat islands' which are warmer due to heat trapped by buildings and concrete).

The Monsoons

The monsoon is a defining feature of India's climate and central to life across the subcontinent, particularly for agriculture. Derived from the Arabic word 'mausim' meaning 'season', the term refers to the seasonal reversal of winds over the Indian Ocean and surrounding landmasses, which brings significant rainfall.

The monsoon mechanism is primarily driven by the differential heating and cooling rates of land and sea. Land heats up and cools down much faster than water.

• Summer (Southwest) Monsoon: During summer, the large Asian landmass heats up significantly, creating a large area of low pressure. The oceans, being cooler, have relatively high pressure. Air naturally flows from high-pressure to low-pressure areas. Thus, moisture-laden winds from the Indian Ocean and the Arabian Sea are drawn towards the heated landmass. As these humid winds rise over the warmer land, the moisture condenses, leading to widespread and often heavy rainfall across the Indian subcontinent. These are the southwest monsoon winds, typically arriving at India's southern tip in early June and covering most of the country by mid-July. The Western Ghats significantly influence this monsoon, causing heavy rain on their western slopes and creating a rain shadow on the eastern Deccan Plateau.
• Winter (Northeast) Monsoon: In winter, the landmass cools down rapidly, becoming cooler than the ocean. This creates a high-pressure system over the land and relatively low pressure over the warmer ocean. Winds then blow from the land towards the ocean. These winds are generally dry, bringing cold conditions to most of India. However, as some of these winds pass over the Bay of Bengal, they pick up moisture and bring rainfall to parts of east and south India (particularly coastal Tamil Nadu and Andhra Pradesh). These are the northeast monsoon winds.

Monsoons are crucial for India's agriculture, determining crop cycles and influencing water availability. Regions like Mawsynram in Meghalaya receive exceptionally high rainfall, holding the record for the highest average annual rainfall globally (around 11,000 mm).

The monsoon phenomenon has also inspired cultural expressions, including specific ragas in Indian classical music associated with rain.

Traditional knowledge about weather prediction, passed down through generations in Indian communities, often includes observations related to animal behavior, plant flowering, or even the placement of bird nests, offering local insights into anticipating monsoon onset and rainfall patterns.

Climate And Our Lives

Climate has a profound and interconnected impact on various aspects of our lives, including culture, economy, and society.

• Culture: India's diverse climate and distinct seasons are deeply woven into its cultural fabric. Numerous festivals and rituals across the country are linked to agricultural cycles, harvest seasons, or the arrival of rain (e.g., Baisakhi, Onam, Pongal, Makar Sankranti, Bihu, Lohri, Chhath Puja, Gudi Padwa, Hemis, Losoong). These celebrations reflect communities' reliance on and reverence for natural cycles.
• Economy: The Indian economy, particularly its large agricultural sector, is heavily dependent on climate patterns, especially the monsoon rainfall. Poor monsoon rainfall (known as 'monsoon failure') can lead to crop losses, water scarcity, migration of agricultural labourers to urban areas, food price increases (inflation), and reduced overall economic activity. Industries also rely on predictable weather and water availability. Extreme weather events can disrupt economic activities and supply chains.
• Society: Climate conditions influence living patterns, housing styles, clothing choices, and food habits in different regions. Climate-related challenges, such as droughts or floods, can lead to displacement of communities and impact social stability. Understanding local climate and traditional coping mechanisms is important for community well-being.

The impact of climate is not only seen in daily life but also becomes critically apparent during climate-related disasters.

Climates And Disasters

India's varied climate makes it vulnerable to various types of natural disasters driven by extreme weather conditions. These events can cause significant loss of life, damage to property and infrastructure, environmental degradation, and economic disruption.

Cyclones

Cyclones are intense tropical storms that form over warm ocean waters, characterized by strong winds rotating around a central 'eye' of low pressure and bringing heavy rainfall. The Indian coastline, particularly the eastern coast along the Bay of Bengal, is frequently affected by cyclones.

Cyclones form when a low-pressure system develops over the sea. Warm, moist air rises, leading to cloud formation and drawing in surrounding air. If conditions are favourable (sufficiently warm water, low wind shear), this system intensifies, winds strengthen and rotate inwards, forming a cyclone with a calm, cloudless 'eye' at its centre. Cyclones can cause extensive damage upon landfall due to high winds, heavy rain, and storm surges.

Organizations like the India Meteorological Department (IMD) monitor cyclone formation and movement, issuing warnings to enable preparedness and evacuation efforts. The National Disaster Response Force (NDRF) plays a crucial role in rescue and relief operations during cyclones and other disasters.

Floods

A flood occurs when an area that is usually dry becomes inundated with water. Causes include excessive rainfall, rivers overflowing their banks, or failure of dams or natural barriers holding water.

Floods are common during the monsoon season in India. Areas prone to riverine flooding include the vast plains watered by major rivers like the Ganga, Brahmaputra, and their tributaries (e.g., parts of Uttar Pradesh, Bihar, Assam). Coastal states like Kerala and Andhra Pradesh can experience floods due to heavy monsoon rainfall or cyclonic activity.

In mountainous regions, floods can be triggered by glacial bursts. These occur when glacial lakes, formed by melting glaciers and dammed by ice or debris, suddenly overflow or burst their banks due to excessive water accumulation (often from rapid melting or heavy rain) and pressure buildup. Glacial bursts can be extremely destructive, causing flash floods downstream, as tragically seen in Uttarakhand in 2013.

Urban flooding can also occur in cities during heavy rainfall, often exacerbated by overburdened or blocked drainage systems, construction on natural waterways, and the prevalence of impervious surfaces like concrete and asphalt that prevent water absorption into the ground.

Landslides

A landslide is the rapid movement of a mass of rock, soil, or debris down a slope. Landslides are frequently triggered by heavy rainfall (which saturates soil and makes slopes unstable), earthquakes, or volcanic eruptions.

Mountainous and hilly regions in India are particularly susceptible to landslides, including the Himalayas (Himachal Pradesh, Uttarakhand, Sikkim, Arunachal Pradesh) and the Western Ghats. Human activities such as deforestation, improper construction on slopes, and building infrastructure without considering geological stability can increase the risk and frequency of landslides, particularly during the monsoon season.

Forest Fires

Forest fires are uncontrolled fires that spread through forests, grasslands, and other vegetation. They are often ignited by natural causes (like lightning) but are frequently caused by human carelessness (e.g., unattended campfires, discarded cigarette butts). Dry climatic conditions, droughts, and high winds contribute to the spread and intensity of forest fires.

States with large forest or grassland areas, including Uttarakhand, Himachal Pradesh, Madhya Pradesh, Chhattisgarh, and regions within the Western Ghats, are prone to forest fires. These fires cause significant environmental damage (destroying forests, harming wildlife, degrading ecosystems) and have economic consequences (loss of timber, disruption of livelihoods, reduced air quality, displacement of communities).

Understanding the causes and impacts of these climate-related disasters is crucial for developing preparedness plans and mitigation strategies at individual, community, and governmental levels.

Climate Change

Climate change refers to significant, long-term shifts in global or regional climate patterns. While Earth's climate has naturally changed over geological time, the current rapid climate change observed since the 19th century is primarily driven by human activities.

The main human activities contributing to climate change include:

• Burning of fossil fuels (coal, petroleum, natural gas) for energy, industry, and transportation.
• Deforestation and land-use change.
• Environmentally harmful industrial practices.
• Patterns of excessive or wasteful consumption.

These activities release large amounts of greenhouse gases (like carbon dioxide) into the atmosphere. While a natural 'greenhouse effect' is essential to warm the Earth, the increased concentration of these gases due to human activity traps excess heat, leading to rapid global warming and disruption of established climate patterns.

The consequences of climate change include rising average temperatures, increased frequency and intensity of extreme weather events (heatwaves, cold waves, droughts, floods, storms), changes in precipitation patterns, sea-level rise, and impacts on ecosystems, agriculture, water resources, and human health.

In India, warmer temperatures are already noticeable, impacting seasonal patterns (shorter, milder winters), agricultural production, and industries. Preparing for these challenges requires understanding the link between climate change causes and the resulting disasters.

Addressing climate change involves two main approaches:

• Mitigation: Taking steps to reduce greenhouse gas emissions and slow down global warming (e.g., transitioning to renewable energy, improving energy efficiency, planting trees, promoting sustainable lifestyles).
• Adaptation: Adjusting to the current and expected impacts of climate change (e.g., building more resilient infrastructure, developing drought-resistant crops, improving early warning systems).

Promoting sustainable practices and building resilience within communities are crucial for facing the challenges posed by climate change, although balancing economic growth with environmental protection remains a complex global challenge.