Social Sciences: Class 7 — Chapter 3: Climates of India

• Weather is what we experience every hour or day (e.g., rain, bright sunshine, wind). It keeps changing constantly.
• Climate is the pattern of weather an area or a region experiences over a long period of time—several decades at least. This pattern varies from region to region.

Seasons occur as the Earth revolves around the Sun. Each season lasts for a few months and recurs every year in a cycle.

Traditionally, in many parts of India, the year is divided into six seasons or ritus:

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

Specific rituals and festivals are associated with these six ritus, such as Vasanta Pañchamī or Śharad Pūrṇima. Human, plant, and animal life are in rhythm with these seasons, affecting the crops grown, food eaten, and clothes worn.

Latitudes measure the distance from the Equator. Places near the Equator (low latitudes) are warmer because the sun's rays hit nearly perpendicularly, focusing energy on a smaller area. Near the poles (high latitudes), the rays are oblique, distributing energy over a larger surface and passing through more atmosphere. In India, southern places like Kanniyakumari and the Nicobar Islands are warm year-round, while northern places like Srinagar are much cooler.

Temperature decreases as altitude increases. This explains why hill stations (e.g., Munnar, Ooty, Shimla, Darjeeling) are cooler than the plains below. This happens because:

1. Atmospheric pressure and air density decrease with altitude; less dense air gets cooler.
2. The sun heats the Earth's surface, so air farther from the surface is less hot.

The sea acts as a moderator for temperature. Coastal areas do not experience extreme temperature variations because land absorbs and loses heat quickly, while the sea absorbs and loses heat slowly. Moving inland leads to extreme temperatures. For example, coastal Mumbai has cooler summers (around $32^\text{C}$) and milder winters (around $18^\text{C}$), while inland Nagpur experiences up to $44^\text{C}$ in summer and $10^\text{C}$ in winter.

Winds move masses of warmer or cooler air. Western winds traveling over deserts from Arabia and Afghanistan bring dry, hot air (heat waves) to northwestern and central India in summer. In winter, cold winds from across the Himalayas bring cold waves. Winds from the sea bring moisture, resulting in rainfall.

The physical surface features (topography) play a major role. The Himalayas and Karakoram ranges protect the Indian subcontinent from cold Central Asian winds. Conversely, the flat topography of the Thar Desert offers no protection from hot, dry winds.

A microclimate is a climate localized in a small area (like enclosed valleys or forests) that differs from the surrounding region. Cities with dense concrete buildings and minimal vegetation trap heat, creating warmer zones known as urban heat islands.

The monsoon is driven by the difference in heating rates between land and water:

• Summer (Southwest Monsoon): The Asian landmass heats up rapidly, creating a powerful low-pressure system. Winds are drawn from the cooler, high-pressure ocean towards the hot land, carrying moisture that condenses and falls as heavy rain. It typically advances from the southern tip of India in early June and covers the subcontinent by mid-July.
• Winter (Northeast Monsoon): The landmass cools down faster than the ocean, reversing the pressure systems. Dry winds blow from the high-pressure land towards the warmer, low-pressure ocean. However, as they pass over the Bay of Bengal, they pick up moisture and bring winter rainfall to parts of eastern and southern India.

• Mawsynram, located in Meghalaya, receives the highest average annual rainfall in the world, about $11,000\text{ mm}$ (11 meters).
• Monsoons have inspired classical Indian ragas, such as Meghamalhār and Amruthavarshini.

Our ancestors developed local traditional knowledge to predict monsoons:

• Fishermen on the Konkan coast predict monsoons when deep-water fish come to the surface.
• In southern India, the monsoon is expected within 50 days of the blossoming of the Golden Shower tree (Cassia fistula).
• Low nests built by crows indicate heavy rainfall, while high nests indicate less rain.

Many Indian festivals are linked to agricultural cycles and seasons, including Bihu, Makar Sakranti, Baisakhi, Pongal, Onam, Lohri, Gudi Padwa, and Chhath Puja. Economically, a 'monsoon failure' leads to agricultural distress, water scarcity, migration of laborers, and food inflation.

Formed when atmospheric pressure near the sea becomes exceptionally low, drawing in high-speed, moisture-laden winds that rotate inward around a cloudless center called the eye of the cyclone. The India Meteorological Department (IMD) tracks these events.

Occur when water overflows onto dry land due to heavy rainfall or breached riverbanks. In the Himalayas, floods can be caused by glacial bursts (e.g., the 2013 Uttarakhand disaster near Kedarnath). Urban flooding is often caused by overburdened drainage systems and concrete surfaces that prevent water absorption.

The sudden collapse of rock, soil, or debris, common in hilly regions like the Himalayas and Western Ghats during monsoons. Human activities like deforestation and unplanned construction increase landslide risks.

Uncontrolled fires spread across vegetation, fueled by dry conditions, droughts, or high winds, often triggered by human carelessness.

• Greenhouse Effect: Gases like carbon dioxide ($\text{CO}_2$) trap heat from the Sun to keep the Earth warm. However, burning fossil fuels, deforestation, and industrial practices have released excessive greenhouse gases, causing rapid global warming.
• Impact in India: Rising temperatures are shortening and milding winters (e.g., early 2025 temperatures were $1\text{ to }3^\text{C}$ above normal), disrupting agriculture and small-scale industries.

• Resilience: The capacity of communities to withstand or recover quickly from climate difficulties.
• Mitigation: Adopting steps to slow down global warming, such as reducing emissions, planting trees, and boosting renewable energy.
• Sustainable Lifestyles: Adopting practices that can be maintained over a long period of time without harming the environment.