Quick Introduction — What you must remember

This chapter explains what weather is — the short-term state of the atmosphere at a place — and the elements that determine it. You will learn how scientists measure weather, how weather differs from climate, and why India’s climate is heavily influenced by the monsoon. The chapter also links weather and climate to human activities, hazards and the idea of climate change.

Elements of Weather — Simple definitions

Temperature

Temperature measures how hot or cold the air is. It is measured by a thermometer (°C). Daily temperature changes depend on time of day, season, altitude, and cloud cover.

Precipitation (Rainfall)

Precipitation includes rain, snow or hail. Measured using a rain gauge, it is the most important factor for agriculture. India receives most of its annual rainfall during the monsoon season.

Humidity

Humidity is the amount of water vapour in the air. A hygrometer measures humidity. High humidity makes hot days feel warmer and affects evaporation and plant transpiration.

Air Pressure

Air pressure is the weight of the air above us, measured in millibars using a barometer. Pressure differences cause wind — air moves from high to low pressure areas.

Wind

Wind is the horizontal movement of air, described by speed and direction. The anemometer measures wind speed. Winds are named by the direction they originate (e.g., northerly winds blow from the north).

Cloudiness & Visibility

Clouds form when moist air rises and cools. Cloud type and amount affect temperature and rainfall. Visibility indicates how far we can see and is reduced in fog or heavy rain.

Weather Instruments & Weather Stations

Modern weather observation combines instruments and stations. A typical weather station records temperature, rainfall, humidity, pressure, wind speed and direction, and sunshine duration. Data from multiple stations help produce weather maps and forecasts.

• Thermometer: Measures air temperature.
• Rain gauge: Measures rainfall amount.
• Barometer: Measures air pressure — useful for predicting storms.
• Anemometer: Measures wind speed; wind vane shows direction.
• Hygrometer: Measures humidity.
• Satellite & Radar: Provide large-scale images of cloud cover and storm systems.

Exam tip: When asked to describe any instrument, mention what it measures and why that measurement matters (e.g., barometer readings fall before storms — helpful for warnings).

Weather vs Climate — Important difference

Weather refers to short-term atmospheric conditions (hours to days) at a location. Climate is the long-term average of weather patterns (decades to centuries) for a region. Example: A rainy day is weather; rainy season patterns over many years describe the climate.

Types of Climate in India — A brief guide

India has a variety of climates due to its size, latitude and relief. Main types include:

• Tropical wet (humid): Coastal regions and the Western Ghats — heavy rainfall and evergreen forests.
• Tropical wet and dry: Much of peninsular India — distinct wet (monsoon) and dry seasons.
• Arid and semi-arid: Thar Desert and surrounding areas — low rainfall.
• Mountain climate: Himalayan regions — colder with snowfall at high altitudes.
• Coastal climate: Moderated temperatures and high humidity along coasts.

Link climate types to crops, housing and clothing when answering exam questions: e.g., heavy rainfall → rice cultivation; mountain climate → warm clothing and terraced farming.

The Indian Monsoon — Key concepts

What is the monsoon?

The monsoon is a seasonal wind system that reverses direction between summer and winter and brings the majority of India’s rainfall. The southwest monsoon (June–September) delivers most rain; the northeast monsoon affects parts of southeast India in October–December.

Why does monsoon occur?

• Differential heating of land and sea during summer creates low pressure over the Indian subcontinent and high pressure over the Indian Ocean; moisture-laden winds move towards the land and rise over hills producing rain.
• The Tibetan Plateau influences wind patterns; the Himalayas act as a barrier helping in rainfall distribution.

Onset, retreat and variability

Onset begins in southern India in June and progresses northwards. Withdrawal happens around September–October. The monsoon’s timing and amount vary yearly, affecting agriculture and water supply.

Exam tip: Mention two factors causing monsoon — differential heating and the role of the Himalayas/Tibetan Plateau — for a concise answer.

How Weather and Climate Affect Our Life

Weather and climate shape agriculture, water resources, health, housing, transport and disasters. Examples:

• Agriculture: Rainfall timing controls sowing and harvest; droughts reduce yields while excess rain causes floods.
• Water resources: Rainfall recharges rivers and groundwater; changes in rainfall patterns affect water availability.
• Health: Weather influences diseases (e.g., malaria increases in wet conditions; heatwaves cause heatstroke).
• Infrastructure: Roads, buildings and power systems are affected by storms, floods and cyclones.

Climate Change & Natural Disasters — A short overview

Climate change refers to long-term changes in average weather patterns, largely driven by greenhouse gas emissions. Impacts include rising temperatures, changing rainfall patterns, more intense heatwaves, and sea-level rise which increase the frequency and severity of natural disasters like cyclones, floods and droughts.

• Adaptation measures: Water conservation, improved forecasting, climate-resilient crops and early warning systems.
• Mitigation measures: Reducing emissions through renewable energy, afforestation and efficient resource use.

For exams, be ready to give one or two examples of climate change impacts and simple measures to reduce risk at local/community level.

Practical Exam Tips & Short Practice Questions

Answer structure: Start with a short definition, list features or causes with bullets, and end with an example or consequence. Use headings and subheadings for clarity.

• Practice Q1: Define humidity and name an instrument to measure it. (Ans: Humidity is water vapour in air; measured by hygrometer.)
• Practice Q2: Why is the southwest monsoon important for India? (Ans: Provides majority of annual rainfall supporting agriculture, groundwater recharge and water supply.)
• Practice Q3: Mention two effects of climate change. (Ans: Increased heatwaves and rising sea levels.)

Map & Diagram Tips

Label the wind direction of the southwest monsoon on a map of India, mark regions with heavy rainfall (western ghats, northeastern states) and show the general path of monsoon onset. For diagrams, a simple sketch of the water cycle (evaporation, condensation, precipitation) helps explain rain formation.