Understanding the Weather — Class 7 Social Science
Exploring Society Part 1 · Chapter 2
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- Mathematics
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2- Mathematics
- Space weighted by chapter size
- Charts from the book's own data
- Traps corrected
- Space weighted by chapter size
- Charts from the book's own data
- Traps corrected
- Space weighted by chapter size
- Charts from the book's own data
- Traps corrected
Chapter summary
Key ideas & terms
- Weather
- The state of the Earth's atmosphere at a particular time and place, described by elements such as temperature, rainfall, wind and humidity.
- Troposphere
- The lowest layer of the atmosphere, closest to the ground, where living things breathe and where almost all weather takes place.
- Precipitation
- Any form of water — rain, snow, sleet or hail — that falls from the sky.
- Atmospheric pressure
- The weight of the air above and around us pressing on the Earth's surface, measured in millibars with a barometer.
- Relative humidity
- A measure of how much water vapour the air holds compared to the maximum it could hold, expressed as a percentage and measured with a hygrometer.
- Meteorology
- The systematic study of weather and how it changes, which forms the basis of weather forecasting.
Extra questions & answers
What is weather, and where does it mostly occur?
Weather is the state of the Earth's atmosphere at a given time and place, and almost all weather phenomena occur in the troposphere, the atmospheric layer nearest the ground.
What are the five elements of weather?
Temperature, precipitation, atmospheric pressure, wind and humidity.
Why do we need common standards to measure temperature?
Because what feels cold to one person may feel pleasant to another; without an agreed scale like Celsius, people in different places cannot share an exact sense of how hot or cold it is.
How is rainfall measured, and in what unit?
With a rain gauge, where rain falls through a funnel into a cylinder and a scale records the depth of water collected, measured in millimetres.
What instrument measures atmospheric pressure, and what does a low reading mean?
A barometer measures it in millibars; normal pressure at the coast is about 1013 mb, and a reading below 1000 mb indicates a depression that may grow into a storm or cyclone.
How do a wind vane and an anemometer differ?
A wind vane shows the direction the wind is blowing from, while an anemometer's spinning cups measure the wind's speed in kilometres per hour.
How did people traditionally forecast weather before instruments?
They observed nature's clues, such as ants shifting their eggs to higher ground, frogs croaking loudly, or pine cones opening and closing, to anticipate rain or storms.
What is an Automated Weather Station (AWS)?
A self-operating system that uses sensors to measure and record temperature, humidity, wind, rainfall and pressure without needing a person present.
When was the India Meteorological Department set up, and what does it do?
It was set up in 1875; it collects weather data, predicts the weather, and issues colour-coded warnings for events like heat waves, heavy rain and cyclones.
Why is accurate weather prediction increasingly important?
It helps people plan activities and lets governments prepare for disasters; this matters more than ever because climate change is making extreme weather such as droughts, floods and cyclones more frequent.
LET'S EXPLORE
What are some of the words in your local language that you use to describe the weather? Hot, cold, warm, chilly, crisp, pleasant, and so on, are commonly used terms in English.
Weather is described differently in every language. In English we say hot, cold, warm, chilly, crisp, pleasant, humid, cloudy etc. In my local language also there are similar words – for example for very hot, very cold, for drizzle, for heavy rain, for windy or foggy weather. You can ask your family which words they use at home for a pleasant cool morning, a scorching afternoon or a rainy evening and make a list with their English meanings.
THINK ABOUT IT
Let us imagine that Krishnan from Chennai is speaking with Amir in Kashmir. Krishnan tells Amir that it has become chilly in Chennai after it rained the previous night. Amir asks him how cold it is. How will Krishnan explain to Amir how cold it is? After all, what is cold for Krishnan may be quite pleasant for Amir!
Krishnan cannot explain cold just by saying chilly because the feeling of chilly is different for a person in Chennai and a person in Kashmir. Chennai is normally very hot, so even
LET'S EXPLORE
What do you think could be some other reasons to measure the weather more precisely? (Hint: Think how knowing the weather a few hours or a few days in advance would help you plan some activities.)
We need precise weather measurement for many practical reasons. Farmers need to know when rain is expected to sow or harvest crops. Pilots, sailors and fishermen need to know about wind and storms for safety. If we know about a heat wave, heavy rain, cyclone or cold wave in advance, we can carry umbrellas, wear the right clothes, store water, or stay indoors. Accurate forecasts also help governments prepare for floods, droughts and to send warnings so people can be safe.
LET'S EXPLORE
Talk to elders in your neighbourhood and ask them how they predict the weather. What signs do they observe? Document any sayings in your regional language that refer to weather prediction.
Elders often use traditional natural signs to predict weather without instruments. They observe ants carrying eggs to higher ground before heavy rain, frogs croaking loudly before rain, birds flying low before a storm, dark clouds gathering, changes in wind direction, or pine cones closing when humidity is high and opening when it is dry. In many villages there are local sayings or proverbs about the monsoon arrival that have been passed down. You can interview grandparents, note the signs they mention and write any regional saying in its original language with its meaning in English.
LET'S EXPLORE
Here's a chart of the temperatures of a city in Madhya Pradesh. What is the maximum temperature recorded in the week shown here? What is the minimum? Calculate the range.
From the table: Maximum temperatures for the week are
Remember the conversation between Krishnan and Amir? If Krishnan said it was 20°C in Chennai and he was feeling a little cold, he and Amir would have a measure they could understand. What do you think Amir’s reaction to Krishnan’s statement might be?
If Krishnan says it is
DON'T MISS OUT
Can you think of a reason why rain arises from the sun?
Yes. The sun heats the Earth, which makes water from oceans, rivers and lakes evaporate into water vapour. The warm vapour rises, cools and condenses to form clouds. When the clouds become heavy they give rain. So the energy for the whole water cycle comes from the sun. That is why the ancient saying says from the sun arises rain, from rain comes food and from food comes life.
LET'S EXPLORE
Make a rain gauge as shown in the diagram above. Place the rain gauge in an open area, away from objects that might obstruct rain. Ensure that the rain gauge is on a flat surface and will not tilt or topple with the wind. Using the measuring scale, record the amount of rainwater collected at the same time every day, for a month. (If there is snow, allow it to melt before taking the measurement.) Calculate the average rainfall for every week in that month and comment on the variation from week to week.
This is a project activity. Make a simple rain gauge with a funnel and a cylindrical bottle marked in millimetres
THINK ABOUT IT
Why do you think it would be important to measure atmospheric pressure? Who are the people most likely to use such measurements?
Atmospheric pressure tells us about the weight of air above us. A sudden fall below about
THINK ABOUT IT
Have you seen seeds like these flying in the wind? What would happen to the seeds if there was no wind?
Yes, many plants make light, fluffy or winged seeds that are carried by wind, like cottony seeds and winged seeds shown in the figure. Wind helps disperse seeds far from the parent plant so they can find space, light and nutrients to grow. If there were no wind, these seeds would fall close to the parent plant, crowd together, and compete for sunlight and water, so fewer new plants would grow and the species would not spread to new areas.
LET'S EXPLORE
Where do you think humidity is likely to be more, Kochi or Jaipur? You might guess that Kochi has higher humidity than Jaipur because it is located near the sea. But how will we know for sure? If we had to compare the humidity level between Kochi and Mangaluru, how would we do it? Discuss with your classmates.
Kochi, being on the coast of Kerala, gets moist air from the sea, while Jaipur is inland in the desert region of Rajasthan with very dry air, so Kochi is likely to have higher humidity. To know for sure we should not guess but measure relative humidity with a hygrometer at both places at the same time and compare the readings in percent
THINK ABOUT IT
If the humidity in Delhi is at 52% while in Kochi it is 84%, in which of the two places are wet clothes likely to dry faster? And where are you likely to sweat more, assuming the temperature is the same in both places?
At
LET'S EXPLORE
Discuss, in pairs, different situations in which weather predictions are helpful. Make a list, and after you have completed it, share it and discuss it with the pair sitting next to you. How many different categories of situations have you been able to identify?
Weather predictions are helpful in many categories: 1) Agriculture – farmers decide when to sow, irrigate and harvest. 2) Safety and disaster management – warnings for cyclones, floods, heat waves and cold waves to evacuate people. 3) Transport – pilots and sailors plan flights and voyages around wind and storms; fishermen avoid going to sea during storms. 4) Daily life – choosing clothes, carrying umbrellas, planning school trips, sports events and weddings. 5) Health – preparing for heat-related illnesses or cold exposure. 6) Industry and energy – managing water supply and electricity demand. You can list these categories and compare with your partner.
LET'S EXPLORE
What do you observe happening on that day? What are the various weather conditions that the IMD is alerting people to?
On 19 May 2024 the India Meteorological Department map shows many simultaneous warnings across India. The legends indicate heat wave, hot and humid, heavy to extremely heavy rain, very heavy rain, hailstorm, thunder and lightning, strong surface winds, dust storm, fog and cold wave conditions in different subdivisions. So the country is experiencing both extreme heat in the northwest and centre and heavy wet weather in the east and south.
Which states have warning signs?
The map uses coloured warning levels. States with Warning (Take Action) or Alert (Be Prepared) shading on that day include many parts of Rajasthan, Gujarat, Punjab, Haryana, Delhi, Uttar Pradesh, Madhya Pradesh, Maharashtra, Karnataka, Kerala, Tamil Nadu, West Bengal, Assam, Meghalaya, Tripura, Lakshadweep and the Northeastern states. The exact subdivisions are marked in red, orange and yellow on the IMD map.
Which parts of India are likely to be free from severe weather?
The subdivisions coloured in green for No Warning are likely to be free from severe weather on that day. These are scattered pockets where none of the listed hazards – heat wave, heavy rain, thunderstorms etc. – were forecast, meaning relatively calm weather.
Which states are likely to face heat wave conditions?
Heat wave symbols are shown over northwest and central India, especially Rajasthan, Punjab, Haryana, Delhi, Uttar Pradesh, Gujarat, Madhya Pradesh and parts of Maharashtra. These states are marked for heat wave and hot and humid warnings on 19 May 2024.
What are the causes for warning in Tripura and Lakshadweep?
According to the icons on the map, Tripura in the northeast is under a warning for heavy to very heavy rain with thunder and lightning, and Lakshadweep off the Kerala coast is under a warning for heavy rain and strong surface winds/thunderstorms associated with monsoon activity over the Arabian Sea.
Questions and activities
(1) Hygrometer
(d) Humidity – Hygrometer measures relative humidity as a percentage, for example
(2) Anemometer
(c) Wind direction and speed – Anemometer with rotating cups measures wind speed in
(3) Barometer
(b) Atmospheric pressure – Barometer measures pressure in millibars
(4) Thermometer
(e) Temperature – Thermometer measures temperature, for example in degrees Celsius
(5) Rain gauge
(a) Precipitation – Rain gauge measures rainfall depth in millimetres
2. Jyotsna is deciding what clothes to pack for her school trip to Mumbai in June. She looks at the weather forecast, which predicts 29°C and 84% humidity. What would be your advice to her?
Mumbai in June is hot and very humid –
3. Imagine that a small group of students is setting up a rain gauge. Here are some options for the site. 1. The school vegetable garden. 2. The terrace of the school building. 3. Open ground with elevated platform. 4. Compound wall of school. 5. Verandah of the school laboratory. Discuss in your group and finalise the site. Write down the reasons for your decision.
The best site is 3. Open ground with elevated platform. A rain gauge must be in an open area where no trees, walls or roofs block rain or cause extra runoff, on flat ground so water does not collect unevenly, and slightly elevated so splashing from the ground does not enter. The terrace may be blocked by walls or give false readings due to wind, the vegetable garden may have irrigation water splashing in, and the compound wall and verandah are sheltered and will block rain. Hence open ground with a stable level platform gives the most accurate measurement.
4. Below is a chart taken from IMD, Jammu and Kashmir. Looking at the data available, write a short script to report the weather conditions in different parts of Jammu and Kashmir on the date shown. (Hint: Cover the temperature range, maximum and minimum temperatures, humidity, precipitation, etc.) Note: ACT means actual; NOR means normal; DEP is departure from normal; R/F is rainfall; S/N is snowfall; TR means trace amount.
Weather report for Jammu and Kashmir on 01-02-2024 evening: All stations were colder than normal. Srinagar recorded a maximum of