With reference to 'water vapour', which of the following statements is/are correct? 1. It is a gas, the amount of which decreases with altitude. 2. Its percentage is maximum at the poles. Select the answer using the code given below:
Contents13
- A1 only
- B2 only
- CBoth 1 and 2
- DNeither 1 nor 2
Show answer
Answer: (A) 1 only
Correct Answer: (a) Statement 1 only.
Statement 1: Water vapour decreases with altitude — ✓ CORRECT.
Water vapour is concentrated in the lower atmosphere and reduces as you go higher.
Statement 2: Water vapour is maximum at the poles — ✗ WRONG.
It's the opposite — water vapour is maximum near the equator (warm, wet tropics — up to 4% of air by volume) and minimum at the poles and deserts (less than 1%).
Key fact: Water vapour decreases both with altitude AND from equator to poles.
It also acts as a natural blanket — absorbing solar radiation and trapping earth's heat.
Water vapour concentration varies dramatically from 4% near the equator to less than 1% at poles, making it the most variable atmospheric component.
UPSC is testing the common confusion between water vapour distribution and ice/snow presence - students wrongly think poles have more water vapour because of visible ice.
Water Vapour Distribution in Atmosphere
Geography water vapour altitude poles
Water Vapour Distribution: Altitude & Latitude Patterns
Water vapour decreases with altitude — concentrated in lower atmosphere
Maximum water vapour at equator (up to 4%), minimum at poles (<1%)
Water vapour acts as natural greenhouse gas — absorbs solar radiation and traps heat
What is Water Vapour
Water vapour is the gaseous form of water in the atmosphere. It's invisible (unlike water droplets in clouds) and varies dramatically by location and altitude. Understanding its distribution helps explain climate patterns worldwide.
Water Vapour Distribution Patterns
Factor | Pattern | Typical Range | Reason |
|---|---|---|---|
Altitude | Decreases upward | Sea level: 0-4% → High altitude: <0.1% | Temperature drops, air can hold less moisture |
Latitude | Decreases poleward | Equator: up to 4% → Poles: <1% | Warmer air holds more water vapour |
Season | Higher in summer | Summer: 2-4% → Winter: 0.5-2% | Temperature controls moisture capacity |
Location | Varies by climate | Deserts: <1% → Tropics: 2-4% | Evaporation rates differ |
Key Properties & Functions
Source: Evaporation from oceans (86%), lakes, rivers, and transpiration from plants
Greenhouse effect: Absorbs longwave radiation from Earth's surface, warming the atmosphere
Condensation nuclei: Forms clouds and precipitation when temperature drops below dew point
Weather patterns: Drives monsoons, cyclones, and regional climate variations
Question Connection
This PYQ tests two fundamental patterns: vertical distribution (Statement 1 - correct) and latitudinal distribution (Statement 2 - incorrect). The trap lies in confusing poles with equatorial regions for maximum moisture.
Trap: Statement 2 reverses the pattern — water vapour is minimum at poles, not maximum
Confusion: Don't mix up ice at poles with water vapour — ice is solid, vapour needs warm air
Memory aid: Think warm = wet vapour, cold = dry air — equator is warm (high vapour), poles are cold (low vapour)
Temperature-Moisture Relationship
Geography
How Temperature Controls Atmospheric Moisture Capacity
Warm air can hold much more water vapour than cold air
Saturation capacity doubles roughly every 10°C temperature rise
Relative humidity = (actual moisture / maximum possible) × 100
The Physics Behind
Temperature controls how much water vapour air can hold before reaching saturation. This explains why tropical regions have high humidity while polar regions remain dry even near ice and snow.
Moisture-Temperature Mechanism
%%{init: {"flowchart": {"wrappingWidth": 460}}}%%
flowchart TD
s1["`**Heat increases molecular energy**
Higher temperature makes water molecules move faster`"]
s2["`**Air expansion creates space**
Warm air expands, providing more room for water molecules`"]
s3["`**Saturation capacity rises**
More water vapour can exist before condensation begins`"]
s4["`**Higher absolute humidity possible**
Actual water content in air increases with temperature`"]
s1 --> s2
s2 --> s3
s3 --> s4Temperature vs Moisture Examples
Location | Average Temp | Water Vapour % | Climate Result |
|---|---|---|---|
Amazon Basin | 27°C | 3-4% | High humidity, frequent rain |
Mediterranean | 18°C | 1-2% | Moderate humidity, seasonal rain |
Siberia | -15°C | <0.5% | Very dry, little precipitation |
Antarctica | -40°C | <0.1% | Extremely dry desert conditions |
Don't confuse: Presence of ice/snow with high water vapour — cold air can't hold much vapour
Common error: Thinking humidity depends only on water sources, ignoring temperature control
UPSC pattern: Questions often test the inverse relationship — where there's lots of water (poles) but little vapour
Global Humidity & Precipitation Patterns
Geography equator poles percentage
World Humidity Distribution: From Equator to Poles
Equatorial regions: Highest humidity (2-4%) due to high temperatures and ocean evaporation
Polar regions: Lowest humidity (<1%) due to extremely cold temperatures
Subtropical deserts: Low humidity despite moderate temperatures due to dry air circulation
Global Humidity Zones
# Global Humidity Distribution
## Equatorial Belt (0°-10°)
- Amazon Basin
- Congo Basin
- Southeast Asia
- High evaporation + High temperature
## Subtropical (20°-30°)
- Sahara Desert
- Australian Outback
- Descending dry air
- Low relative humidity
## Temperate (30°-60°)
- Europe
- North America
- Moderate humidity
- Seasonal variation
## Polar (60°-90°)
- Antarctica
- Arctic
- Extremely low vapour
- Cold air limitationWorld Humidity Distribution
World map showing atmospheric humidity distribution with color-coded zones from high humidity equatorial regions to low humidity polar areas
Notice how humidity follows temperature patterns — maximum at hot equator, minimum at cold poles
India's Humidity Patterns
Monsoon influence: Southwest monsoon brings 4% humidity to Western Ghats during summer
Desert regions: Thar Desert maintains <1% humidity despite being in tropics
Altitude effect: Hill stations like Shimla have lower humidity than plains despite same latitude
Seasonal variation: Humidity ranges from 30% (winter) to 90% (monsoon) in most regions
Geographic trap: Don't assume coastal = high humidity — depends on temperature and wind patterns
Altitude confusion: Mountain regions can be dry despite being near water sources
Seasonal reversal: Some regions are more humid in winter due to local weather patterns