Forms of Precipitation: Rain, Snow, Hail
In Kashmir snow falls in winter, here water falls in the rainy season and sometimes hailstones suddenly hit fields. All these things falling from the sky belong to one family.
Water falling from clouds to the ground in liquid or solid form is precipitation. Rain, snowfall and hail are its main forms.
Key idea 1 : Snowfall — When air temperature falls below freezing, vapour turns directly into snow crystals; this is sublimation. In high latitudes and temperate regions snow falls even at sea level; in the tropics only above the snowline. Snow does not flow, it piles in layers. When heavy, it stops transport and communication, but on melting it gives water to the region.
Key idea 2 : Difference between ice and snow — Snow is loose and opaque. Pressure of upper layers makes lower layers uniform, hard and transparent; this is ice. When temperature falls below 0 °C a layer of ice forms on a lake; it is not directly related to snowfall.
Key idea 3 : How hail falls — When the ground is very hot, air rises fast, cools and vapour condenses forming dark clouds. Water drops rise high and freeze. Heavy hailstones start to fall but the upward air throws them up again, each time adding a new layer of ice. After many rounds the stone grows big and finally hits the ground hard. Crops may be destroyed.
- Easy : Vapour turning directly into snow crystals? — Sublimation.
- Medium : What increases the layers of hail? — Being tossed up by air.
- Exam-type : In which season does hail fall in India? — Summer.
In the figure: Rain, snow and hail.
Snow = vapour → ice crystals; hail = tossed up and down and grows in layers.
Ice and snow are not the same; snow is loose, ice is hard and transparent.
Memory clue: Snow = sublimation; hail = layer on layer. Memory clue: "Snow is light, hail is heavy".
Spot the difference
| Form | State | Special point |
|---|---|---|
| Rain | Liquid | Water for farming |
| Snow | Solid, loose | Formed by sublimation |
| Hail | Solid, layered balls | Crop damage |
Practice questions
- 1What is precipitation?
- 2State the main forms of precipitation.
- 3What is sublimation?
- 4State the difference between ice and snow.
- 5How is hail formed?
- 6Why do hailstones have layers?
- 7State good and bad effects of heavy snowfall.
- 8Why does it not snow in Maharashtra?
Show answers (try them yourself first)
- 1Water falling from clouds as liquid or solid.
- 2Rain, snowfall, hail.
- 3Direct change of vapour into ice crystals.
- 4Snow is loose; ice is hard and transparent.
- 5Drops freeze in the upper air and fall as heavy stones.
- 6Because a new layer is added each time they are tossed up and down.
- 7Good: water on melting; bad: transport blocked.
- 8Because temperature does not fall low enough and the region is below the snowline.
Types of Rainfall
When the lid of a hot pot in the kitchen is lifted, steam rises and drops stick to the lid. On a huge scale the same happens in the atmosphere and it rains.
Moist air rises, cools, condenses and forms clouds. When drops become heavy they fall as rain. By the reason for air rising there are three types: convectional, orographic and cyclonic.
Key idea 1 : Convectional rainfall — In equatorial regions the ground and the air near it are heated by the sun, become light, rise and cool. Cool air holds less vapour so condensation occurs and it rains. There it rains almost every afternoon with lightning and thunder. The Congo basin of Africa and the Amazon basin of South America are examples.
Key idea 2 : Orographic rainfall — Moist winds from the sea or lakes are blocked by high mountain ranges, rise along the slope, cool and give rain. The side facing the wind gets more rain. After crossing the mountain the air has lost vapour and warms and dries; so the far side gets less rain; this is the rain-shadow area. Monsoon rainfall in India is orographic.
Key idea 3 : Cyclonic rainfall — Where air pressure is lower than the surroundings a cyclone forms. Air from around comes to the centre, rises, cools and rains. In temperate regions it is wide; in the tropics it is limited and stormy. Most of the world gets orographic rain; convectional rain falls in certain regions and is certain; orographic and cyclonic rain are uncertain so floods and droughts can come often.
- Easy : On the windward side of a mountain is rain more or less? — More.
- Medium : Daily afternoon rain with thunder where? — Equatorial regions.
- Exam-type : Rain around a low pressure centre? — Cyclonic.
In the figure: Three types of rainfall.
Heated → convectional; mountain blocks → orographic; low pressure → cyclonic.
A rain-shadow area is not one without rain; it only gets less rain.
Memory clue: Heat-Hill-Hurricane. Memory clue: "Heated, blocked, swirled".
Spot the difference
| Type | Reason | Example |
|---|---|---|
| Convectional | Heating of ground | Congo, Amazon basin |
| Orographic | Mountain barrier | Indian monsoon rain |
| Cyclonic | Low pressure centre | Temperate belts |
Practice questions
- 1Which are the types of rainfall?
- 2How does convectional rainfall occur?
- 3How does orographic rainfall occur?
- 4What is a rain-shadow area?
- 5When does cyclonic rainfall occur?
- 6Which rainfall is found most in the world?
- 7State the rainfall type of Maharashtra and where the rain shadow lies.
- 8Why do you think afternoon convectional rain is less in oceanic equatorial areas?
Show answers (try them yourself first)
- 1Convectional, orographic and cyclonic.
- 2Heated air rises, cools and condenses.
- 3Moist winds are blocked by mountains, rise and cool.
- 4The low-rain part on the far side of the mountain.
- 5Where a cyclone forms.
- 6Orographic rainfall.
- 7Orographic; rain shadow lies east of the Sahyadri.
- 8The sea surface does not heat as fast as the land.
Measuring Rainfall
If an empty tin is kept in the open school ground it holds water after rain. Measuring its depth tells how much it rained. A rain gauge does this work carefully.
The instrument that measures rainfall is a rain gauge. Rain is measured in millimetres. The amount of rain depends on amount of vapour, air pressure, temperature, relief and latitude.
Key idea 1 : How a rain gauge is built — A funnel of fixed diameter collects rain in a bottle, which is poured into a measuring jar and read in millimetres. The gauge is kept in the open on a 30 cm high mound so water is collected without obstruction. In heavy rain areas readings are taken every three hours.
Key idea 2 : What is 1 mm of rain? — If 1 mm of rain falls and the water does not run off, soak in or evaporate, 10 lakh litres of water collect on 1 sq km. Snow can also be measured with a rain gauge; it is carefully melted and the water is measured.
Key idea 3 : Factors affecting rainfall — The amount of rainfall depends on vapour in the atmosphere, air pressure and temperature. Relief of the land and latitude of the place also matter. So areas of heavy rainfall are found in the tropics.
- Easy : If 1 mm of rain falls over 2 sq km, how many litres? — 20 lakh litres.
- Medium : 5 mm of rain over 1 sq km means how much? — 50 lakh litres.
- Exam-type : On how high a mound is the gauge kept? — 30 cm.
In the figure: Working of a rain gauge.
According to Guinness records Mawsynram in Meghalaya has the world’s highest average annual rainfall (about 11,870 mm); some sources say other places compete for this title. As per the textbook a 120 mm layer of snow is taken equal to 10 mm of rain. (Check with the textbook)
1 mm × 1 sq km = 10 lakh litres.
A rain gauge should not be kept under trees or next to buildings; it is kept in the open.
Memory clue: 1 mm = 10 lakh litres per sq km. Memory clue: "One mm, a million litres".
Spot the difference
| Part | Work | Special point |
|---|---|---|
| Funnel | Collects water | Fixed diameter |
| Measuring jar | Measures water | Reads in mm |
| Mound | Gives open space | 30 cm high |
Practice questions
- 1What is a rain gauge?
- 2Which are the parts of a rain gauge?
- 3Why is a rain gauge kept in the open?
- 4How much water per sq km is 1 mm of rain?
- 5If 3 mm of rain falls over 4 sq km, how many litres of water?
- 6How is snow measured?
- 7State factors affecting the amount of rainfall.
- 8Write how you will record a week’s rainfall and draw a bar graph.
Show answers (try them yourself first)
- 1An instrument measuring rainfall.
- 2Funnel, bottle, measuring jar, mound.
- 3So water is collected without obstruction.
- 410 lakh litres.
- 51.2 crore litres (120 lakh).
- 6The water obtained from melted snow is measured.
- 7Vapour, pressure, temperature, relief, latitude.
- 8Record mm daily, draw 7 bars, height = rainfall.
Fog, Dew, Frost and Effects of Precipitation
On winter mornings drops of water sparkle on grass blades and distant things vanish. Without rain the crop dries and too much rain brings floods. The effects of precipitation are tied to our life like this.
When vapour condenses or freezes near the ground we see fog, dew or frost. Too little or too much precipitation brings drought or floods.
Key idea 1 : Fog, dew and frost — Air near the ground cools and vapour condenses into tiny water particles that float; when their density rises fog forms. When moist air touches a very cold object drops settle on it; this is dew. If air temperature is below 0 °C these drops freeze; this is frost. Dew and frost are more in winter.
Key idea 2 : Effects of precipitation — Precipitation is the main source of drinking water. Heavy rain brings floods and loss of life and property; no rain brings drought, food shortage, trouble for farmers and effect on the economy. Indian farming depends largely on the monsoon. Good rain at the right time raises production but India’s rain is erratic.
Key idea 3 : Effects of fog and acid rain — Dense fog reduces visibility; roads, railways, waterways and air transport suffer, accidents happen and trains and flights are cancelled. Frost damages crops and makes roads slippery. Industrial pollution mixes gases in air which react with vapour to form nitric and sulphuric acids. When these fall with rain it is acid rain; it harms living and non-living things.
- Easy : Drops of vapour settled on a cold object; what? — Dew.
- Medium : Below 0 °C dew freezes; what is it called? — Frost.
- Exam-type : Condition due to no rain? — Drought.
In the figure: Three forms of vapour near the ground.
Fog = floats; dew = sticks; frost = sticks and freezes.
Dew does not fall from the sky; it forms by vapour condensing on a cold object.
Memory clue: Floats = fog; sticks = dew; freezes = frost. Memory clue: "Float, Stick, Freeze".
Spot the difference
| Type | How formed | Effect |
|---|---|---|
| Fog | Tiny particles float in air | Low visibility, accidents |
| Dew | Condensation on cold object | Harms some crops, helps some |
| Frost | Dew freezes below 0 °C | Crop damage |
Practice questions
- 1How is fog formed?
- 2State the difference between dew and frost.
- 3State effects of precipitation on human life.
- 4Explain the effect of monsoon rain on Indian farming.
- 5What problems does dense fog cause?
- 6How is acid rain formed?
- 7What are the ill effects of acid rain?
- 8Write causes and remedies of drought and floods.
Show answers (try them yourself first)
- 1Vapour condenses into tiny particles that float near the ground.
- 2Dew = drops; frost = frozen drops (below 0 °C).
- 3Drinking water, farming; floods and drought.
- 4Rain at the right time raises yield; otherwise loss.
- 5Low visibility, accidents and cancelled transport.
- 6Gases from pollution react with vapour to make acids.
- 7Harm to living things and buildings.
- 8Causes: erratic rain; remedies: dams, water storage, planting trees.