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CBSESecondary School (English Medium) Class 7
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Syllabus

Weather and Climate

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Topics

  • Introduction
  • Weather related / Climatic factors
  • Changes in Weather

Introduction

  1. Weather: Weather refers to the atmospheric conditions, such as temperature, humidity, wind, and rainfall, at a specific time and place. It can change quickly, even within a few hours or days. For example, you might say, “It’s sunny in the morning but raining in the afternoon.” Weather describes short-term changes in the atmosphere that we experience daily.
  2. Climate: Climate is the average weather conditions of a specific region recorded over a long period, usually 30 years or more. It gives a general idea of what the weather is usually like in that area. For example, a desert has a hot and dry climate, while a polar region has a cold climate. Climate represents the long-term patterns and trends in atmospheric conditions.

Weather related / Climatic factors

  1. Atmospheric Pressure: Atmospheric pressure is the weight of air pressing down on the Earth's surface. It changes with altitude, temperature, and humidity. High pressure generally brings clear skies, while low pressure often leads to cloudy or rainy weather. It is measured using a barometer and expressed in millibars (mb) or atmospheres. Variations in atmospheric pressure are key drivers of winds and storms.
  2. Temperature: Temperature measures how hot or cold the air is at a particular time and place. It influences weather patterns, determining factors like evaporation, wind flow, and precipitation. It is measured in degrees Celsius (°C) or Fahrenheit (°F) using a thermometer. Temperature changes during the day, seasons, and geographical regions. It directly affects human activities, crops, and ecosystems.
  3. Sunlight: Sunlight is the primary source of energy for Earth, influencing temperature and weather patterns. It affects photosynthesis in plants, heating the land, air, and water, which drives processes like evaporation and wind. The intensity of sunlight varies with time of day, latitude, and seasons. Less sunlight can cause cooler temperatures, while more sunlight leads to warming.
  4. Clouds: Clouds are formed when water vapour condenses into tiny water droplets or ice crystals in the atmosphere. They play a major role in weather by bringing precipitation like rain, snow, or hail. Clouds also affect the temperature by blocking sunlight during the day and trapping heat at night. Different types of clouds (e.g., cumulus, stratus, cirrus) indicate specific weather conditions.
  5. Humidity: Humidity refers to the amount of water vapour present in the air. It determines how "moist" or "dry" the atmosphere feels. High humidity makes the air feel warmer and can lead to cloud formation and rainfall. It is measured using a hygrometer and expressed as a percentage. Humidity is critical for determining weather conditions like fog, dew, or thunderstorms.
  6. Rainfall: Rainfall occurs when water vapour in clouds condenses into droplets that fall to the ground. It is a key factor in determining the water availability for plants, animals, and humans. Rainfall is measured in millimetres (m) using a rain gauge. It varies with location, season, and atmospheric conditions. Too much rainfall causes floods, while too little can lead to droughts.
  7. Visibility: Visibility refers to how far one can see clearly in the atmosphere. It is affected by factors like fog, rain, dust, smoke, or pollution. Poor visibility is common during heavy fog or storms and can disrupt transportation, including road, air, and sea travel. High visibility usually occurs during clear weather with minimal air particles.
  8. Wind: Wind is the movement of air from high-pressure to low-pressure areas. It affects weather by transporting heat, moisture, and pollutants across regions. Wind speed and direction are measured using an anemometer and a wind vane. Winds play a role in storms, monsoons, and other large-scale weather phenomena.

Changes in Weather

  1. Weather refers to atmospheric conditions at a specific location and time, while climate remains constant in a region for a long duration.
  2. Weather changes frequently over short periods, whereas climate changes slowly over much longer durations.
  3. Climate significantly impacts human life by influencing basic needs like food, clothing, and shelter.
  4. It plays an essential role in occupations, particularly in agriculture, as seen in agrarian countries like India.
  5. Temperature, wind speed and direction, and atmospheric pressure are crucial climatic factors.
  6. These climatic factors are considered during the construction of infrastructure such as runways, seaports, bridges, and skyscrapers.
  7. Understanding weather and climate helps in planning daily activities and long-term developments.
  8. Climate determines the overall lifestyle, occupations, and economic activities of people in a particular region.
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