Chapter Notes

Weather, Seasons and the Climate

It's common to hear people use the words weather and climate interchangeably, but they actually have different meanings. Weather is what we experience on a daily basis – a rainy morning, a sunny afternoon, or a windy evening. Weather is constantly changing.

Climate, on the other hand, is the long-term pattern of weather in a specific area or region, usually over several decades. Climate describes the typical weather conditions you can expect in a place.

Seasons

Seasons happen because the Earth revolves around the Sun. Each season lasts for a few months and comes back every year. Most regions of the world experience four main seasons: spring, summer, autumn, and winter.

India is unique because it experiences rainfall during a specific period called the monsoon or rainy season, in addition to the other four seasons.

In many parts of India, the year is traditionally divided into six seasons, also known as ṛitus:

• Vasanta (spring)
• Grīṣhma (summer)
• Varṣhā (rainy season)
• Śharad (autumn)
• Hemanta (pre-winter)
• Śhiśhir (winter)

Specific rituals and festivals are connected with these six ṛitus, such as Vasanta Pañchamī or Śharad Pūrṇima.

Human, plant, and animal life are closely connected to the seasons. The crops we grow, the food we eat, and the clothes we wear all change with the season. Trees and shrubs may bloom in spring, shed leaves in autumn, and animals grow thicker fur in winter, depending on the region.

Changes in Climate

While climate is generally stable over long periods, scientists have observed changes in the world's climates in recent decades. Studies indicate that many of these changes are caused by human actions.

To recap:

• Weather is our day-to-day experience – windy, rainy, hot, dry, etc.
• Seasons recur every year, and the weather changes with each season.
• Climate is the long-term weather pattern in a specific region.

Types of Climates in India

India is known for its diversity, and this extends to its climate as well.

• Alpine Climate: In the northern Himalayan mountains, there is an alpine climate with cold, snowy winters and cool summers.
• Temperate Climate: Lower in the Himalayas and in many hilly areas, the climate is temperate, with moderately cold winters and not-too-hot summers. These areas are home to many "hill stations" where people go to escape the heat of the plains.
• Subtropical Climate: The northern plains have a subtropical climate with very hot summers and cold winters. This region is where most of India's wheat is grown.
• Arid Climate: The Thar Desert in the west has an arid climate with extremely hot days, cool nights, and very little rainfall. People in this region have developed unique ways to collect and save water.
• Tropical Wet Climate: The western coastal strip receives heavy rainfall during the monsoon months, creating a tropical wet climate that is favorable for growing rice and spices.
• Semi-Arid Climate: The central Deccan Plateau has a semi-arid climate with hot summers, mild winters, and moderate rainfall during the rainy season.
• Tropical Climate: Eastern India and the southern peninsula experience a tropical climate with a mild winter and distinct wet and dry periods controlled by monsoon winds.

Factors Determining the Climate

Several factors determine the different climates we find in India. These factors can be general (affecting the entire planet) or regional/local.

Latitude

Latitude measures the distance from the Equator. Places near the Equator (low latitudes) are warmer, while places near the poles (high latitudes) are colder.

This is because the sun's rays hit the Earth at different angles. At the Equator, the rays are nearly perpendicular, focusing their energy on a smaller area. Near the poles, the rays are more angled, spreading the energy over a larger area.

Altitude

Altitude, or height above sea level, also affects temperature. Hill stations are cooler than the plains below because temperature decreases as altitude increases.

There are two reasons for this:

1. Atmospheric pressure and air density decrease with altitude, making the air cooler.
2. The sun heats the Earth's surface, so the farther away from the surface, the less hot the air will be.

Proximity to the Sea

Coastal areas have more stable temperatures – not too hot in summer and not too cold in winter. This is because the sea acts as a moderator for temperature.

Water heats up and cools down more slowly than land. During the summer, the sea absorbs heat, keeping coastal areas cooler. During the winter, the sea releases heat, keeping coastal areas warmer.

As you move inland, temperatures become more extreme, with hotter summers and colder winters.

Winds

Winds can move masses of warm or cool air.

• Winds from the west, traveling over the deserts of Arabia and Afghanistan, bring dry and hot air to states like Punjab, Haryana, Rajasthan, and Madhya Pradesh, causing heat waves in summer.
• Cold winds from across the Himalayas creep into the Himalayan foothills in winter, resulting in cold waves.

Winds also affect humidity and precipitation. Winds coming from the sea bring moisture and can cause rainfall.

Topography

Topography, the physical surface features of an area, plays an important role in determining climate.

• The Himalayas and Karakoram ranges protect the Indian subcontinent from the cold winds of Central Asia.
• The flat topography of the Thar Desert leaves it exposed to hot, dry winds.

Putting it all Together

The climate of any region is determined by all the factors above. Describing a climate involves looking at patterns of temperature, precipitation (rain or snowfall, fog or mist), and wind conditions over three decades or more.

A microclimate is a localized climate in a small area that differs from the surrounding region. Enclosed valleys, some forests, and "urban heat islands" (cities with lots of buildings and little vegetation) can have their own microclimates. Microclimates can influence local plant and animal life, crops, and human health.

The Monsoons

The monsoon season is vital to life in India. During the monsoon months, rivers fill up, the soil is soaked, crops grow, and life thrives.

The word "monsoon" comes from the Arabic word "mausim," meaning "season." It refers to seasonal winds over a large area of the Indian Ocean and surrounding regions, including Australia, Africa, and South Asia.

Monsoons have a yearly pattern based on the fact that land heats up and cools down faster than the ocean.

• In summer, the Asian landmass heats up, creating a low-pressure system. Winds are drawn from the cooler, high-pressure ocean towards the hot land, carrying moisture that condenses and falls as monsoon rains.
• In winter, the landmass cools down faster than the ocean. The land has a high-pressure system, while the ocean remains warmer with lower pressure. This causes winds to blow from the land towards the ocean, bringing dry conditions.

Monsoons in India

In India, the monsoon rains typically arrive at the southern tip of India in early June and move northward, covering the entire subcontinent by mid-July.

The Western Ghats act as a natural barrier. Their western slopes receive a lot of rainfall, while the Deccan Plateau to the east receives less. This is called the summer or southwest monsoon.

As winter approaches, the winds reverse and blow from the land to the ocean. These dry winds bring cold weather to south India. However, some of these winds pass over the Bay of Bengal, collect moisture, and bring rainfall to parts of east and south India. This is called the winter or northeast monsoon.

Climate and our Lives

Our lives are deeply connected to the climate.

• Local cultures reflect the impact of climate, with many Indian festivals associated with seasons and agricultural activities.
• The climate has a direct impact on the economy. "Monsoon failure" (poor rainfall) can lead to agricultural problems, water shortages, migration of agricultural workers, and increased food prices.
• Industrial activity also depends on predictable weather and water availability.

Climates and Disasters

India's diverse weather patterns can cause extreme conditions such as cyclones, floods, landslides, and other climate-related disasters.

Cyclones

The Indian coastline, especially the eastern coast, experiences several cyclones every year. Cyclones can be destructive, causing loss of life, damage to property, uprooting trees, and soil erosion. The India Meteorological Department (IMD) tracks cyclones and provides information about their formation, evolution, and path.

Cyclones form when the atmospheric pressure near the sea becomes lower than the surrounding areas, creating a low-pressure system. Air from surrounding areas rushes into the low-pressure area, bringing moisture and rain. When the low-pressure system is intense and wind speeds are high, a cyclone can form.

As winds collect moisture, they form clouds and rotate inwards towards the center of the depression. This cloudless center is called the eye of the cyclone.

Floods

A flood occurs when water overflows into normally dry land. This can be due to heavy rainfall, excessive water accumulation in rivers and lakes, or breached banks. Floods occur frequently during the monsoons. Uttar Pradesh, Bihar, Kerala, Andhra Pradesh, and Assam are particularly vulnerable.

In the Himalayan regions, floods can occur when glacial lakes overflow due to rapid melting or heavy rainfall. This is called a glacial burst and can have devastating consequences.

Many cities experience flooding due to overburdened drainage systems, poorly planned construction blocking waterways, and urban surfaces that prevent water absorption.

Landslides

A landslide is the sudden collapse of rock, soil, or debris, often triggered by heavy rain, earthquakes, or volcanic activity. Landslides are common in hilly and mountainous regions such as Himachal Pradesh, Uttarakhand, Sikkim, Arunachal Pradesh, the Western Ghats, and other hilly regions, especially during the monsoon.

Human activities like deforestation, poorly planned infrastructure, and excessive construction increase the risk of landslides.

Forest Fires

Forest fires are uncontrolled fires that spread rapidly across vegetation, often fueled by dry conditions, droughts, or high winds. Human carelessness is another common cause. Forest fires are common in states with large forested areas, such as Uttarakhand, Himachal Pradesh, Madhya Pradesh, Chhattisgarh, and mountain ranges like the Western Ghats.

Forest fires destroy forests, harm wildlife, degrade ecosystems, pollute the air, and displace local communities.

Climate Change

Climate change refers to significant, long-term changes in the climate, either globally or regionally. This includes shifts in temperature, precipitation, and weather events.

While climate change occurred naturally in the past, since the 19th century it has been largely driven by human activities, particularly:

• Burning fossil fuels (coal, petroleum oil, and natural gas)
• Deforestation
• Environmentally harmful industrial practices
• Excessive consumption

Burning fossil fuels releases carbon dioxide (CO2) and other greenhouse gases into the atmosphere. These gases trap heat from the sun, causing the greenhouse effect, which warms the Earth. However, the sudden increase in greenhouse gases from human activities is causing rapid global warming and disrupting climate patterns.

In India, rising temperatures are already noticeable. For example, in early 2025, the country's average temperature was significantly above normal, resulting in a shorter and milder winter. This affects agriculture and small-scale industries.

Understanding the causes of climate change and its link to disasters can help us prepare for future challenges. It also highlights the need for more environment-friendly practices and building resilience (the ability to recover quickly from difficulties) and adaptation in communities.

Governments worldwide, including India's, are attempting to promote mitigation measures (steps to slow down global warming), such as:

• Reducing greenhouse gas emissions
• Planting trees
• Boosting renewable energy
• Improving energy efficiency
• Promoting sustainable lifestyles (practices that can be maintained over a long period)

However, these efforts often conflict with the desire for economic growth and increased consumption.