What could be the main reason/reasons of the formation of African and Eurasian desert belt? 1. It is located in the sub-tropical high pressure cells. 2. It is under the influence of warm ocean currents. Which of the statements given above is/are correct in this context?

Updated 11 Apr 2026

Contents20

UPSC Prelims GS2011Geography

A1 only
B2 only
CBoth 1 and 2
DNeither 1 nor 2

Show answer

Answer: (A) 1 only

Statement 1 is CORRECT:

The African-Eurasian desert belt (Sahara, Arabian, Thar, etc.) lies in the SUBTROPICAL HIGH-PRESSURE ZONE (around 20°-30° N latitude).

In this zone, air descends from high altitudes → descending air gets compressed and heated → it can hold more moisture instead of releasing it → NO rainfall → desert formation.

This is called the 'Hadley Cell' mechanism.

Statement 2 is WRONG:

WARM ocean currents actually bring MOISTURE and rainfall to nearby coasts (e.g., Gulf Stream warms Western Europe).

It's COLD ocean currents (like Canary Current off Sahara, Benguela Current off Namib Desert) that cause coastal deserts by cooling the air and preventing evaporation.

So warm currents are the OPPOSITE of what causes deserts.

Key concept:

Subtropical deserts = high pressure (descending dry air).
Coastal deserts = cold ocean currents.

Why this was asked

The African-Eurasian desert belt (Sahara, Arabian, Thar deserts) forms due to the subtropical high-pressure zone around 20°-30° N latitude where descending air gets compressed, heated, and cannot release moisture.

Warm ocean currents bring moisture and rainfall to coasts, while cold ocean currents like the Canary Current off Sahara actually create coastal deserts by cooling air and preventing evaporation.

Subtropical High Pressure Belt

Geography sub-tropical high pressure cells subtropical

Subtropical High Pressure Belt: Desert Formation Mechanism

Must know

Located at 20°-30° latitude in both hemispheres

Descending air creates high pressure and dry conditions

Forms world's major hot deserts: Sahara, Arabian, Thar, Kalahari

Good to know

Part of Hadley Cell circulation pattern

Desert Formation Process

The subtropical high pressure belt is the primary reason for the world's major hot deserts. This zone experiences subsiding air from the upper atmosphere, which compresses and heats up as it descends, creating stable high-pressure conditions that prevent rainfall.

How High Pressure Creates Deserts

%%{init: {"flowchart": {"wrappingWidth": 460}}}%%
flowchart TD
  s1["`**Air rises at Equator**
Hot air ascends due to intense heating`"]
  s2["`**Air moves poleward**
Upper atmospheric air flows toward 30° latitude`"]
  s3["`**Air descends at 30°N/S**
Cool air sinks creating high pressure`"]
  s4["`**Adiabatic warming**
Descending air compresses and heats up`"]
  s5["`**Increased moisture capacity**
Warm air holds more water vapor, no precipitation`"]
  s6["`**Desert conditions**
Clear skies, low humidity, minimal rainfall`"]
  s1 --> s2
  s2 --> s3
  s3 --> s4
  s4 --> s5
  s5 --> s6

Major Subtropical Deserts

Desert	Location	Latitude	Continent
Sahara	North Africa	20°-30°N	Africa
Arabian	Middle East	20°-30°N	Asia
Thar	India-Pakistan	25°-30°N	Asia
Kalahari	Southern Africa	20°-30°S	Africa
Atacama	Chile-Peru	20°-30°S	South America
Great Victoria	Australia	25°-32°S	Australia

Global Pressure Belts

Subtropical high pressure cells at 30°N and 30°S create the world's major hot desert belt

Source: PMF IAS — Atmospheric Pressure Belts and Wind Systems - PMF IAS · www.pmfias.com

Exam traps

Trap: Confusing subtropical deserts (caused by high pressure) with coastal deserts (caused by cold currents)

Trap: Thinking warm ocean currents cause deserts - they actually bring moisture and rainfall

Trap: Forgetting the Hadley Cell mechanism - air must rise at equator and descend at 30° latitude

Ocean Currents & Climate Impact

Geography warm ocean currents

Ocean Currents: Warm vs Cold Climate Effects

Must know

Warm currents bring moisture and moderate temperatures to coasts

Cold currents create coastal deserts by cooling air masses

Statement 2 is WRONG - warm currents don't cause deserts

Good to know

Examples: Gulf Stream (warm), Canary Current (cold)

Climate Impact Mechanism

Ocean currents significantly influence coastal climates through temperature regulation and moisture transport. The key distinction is that warm and cold currents have opposite effects on precipitation patterns and desert formation.

Warm vs Cold Ocean Currents

Factor	Warm Currents	Cold Currents
Temperature Effect	Raise coastal temperatures	Lower coastal temperatures
Evaporation	Increase evaporation	Reduce evaporation
Moisture Content	Carry more water vapor	Carry less water vapor
Precipitation	Increase rainfall	Decrease rainfall
Climate Created	Humid, moderate	Arid, coastal deserts
Example Current	Gulf Stream, Kuroshio	Canary, Benguela, Peru
Coastal Effect	Western Europe warmth	Sahara, Namib, Atacama deserts

Why Statement 2 is Wrong

Warm currents increase evaporation and bring more moisture to coastal areas

Examples: Gulf Stream makes Western Europe warmer and wetter than expected

Cold currents cool the air, reducing its moisture-holding capacity

Cold currents create coastal deserts: Canary Current → Sahara coast, Peru Current → Atacama Desert

Global Ocean Currents

Notice how cold currents (blue) align with coastal deserts, while warm currents (red) bring moisture

Source: MapsforUPSC — Ocean Currents: Map, Types, Causes & Key Facts – UPSC · mapsforupsc.com

Exam traps

Trap: Assuming 'warm' ocean currents cause deserts - they actually prevent desert formation

Trap: Confusing coastal desert formation (cold currents) with interior desert formation (high pressure)

Trap: Not knowing specific examples - Canary Current causes Sahara's coastal aridity

African-Eurasian Desert Belt

Geography African and Eurasian desert belt

African-Eurasian Desert Belt: World's Largest Arid Zone

Must know

Largest continuous desert belt spanning Africa and Asia

Includes Sahara, Arabian, Thar and Iranian deserts

Located between 20°-30°N latitude in subtropical high pressure zone

Good to know

Extends from Atlantic coast of Africa to Pakistan

Geographic Extent

The African-Eurasian desert belt forms the world's most extensive arid region, stretching approximately 12,000 km from Morocco's Atlantic coast to Pakistan's Thar Desert. This continuous belt demonstrates how subtropical high pressure creates consistent desert conditions across vast continental areas.

Major Deserts in the Belt

Desert	Country/Region	Area (approx.)	Key Features
Sahara	North Africa	9 million km²	World's largest hot desert
Libyan Desert	Libya, Egypt	1.1 million km²	Part of Sahara, extremely arid
Arabian Desert	Saudi Arabia, UAE	2.3 million km²	Rub' al Khali (Empty Quarter)
Thar Desert	India, Pakistan	200,000 km²	Great Indian Desert
Dasht-e Kavir	Iran	77,000 km²	Great Salt Desert
Dasht-e Lut	Iran	51,000 km²	Hottest surface temperatures recorded

Formation Factors

# African-Eurasian Desert Belt
## Primary Cause
- Subtropical High Pressure
- Descending Air Masses
- 20°-30°N Latitude
## Geographic Factors
- Continental Interior
- Distance from Ocean
- Rain Shadow Effects
## Atmospheric Circulation
- Hadley Cell
- Trade Winds
- Anti-cyclonic Conditions

Desert Belt Map

Satellite or relief map showing the continuous African-Eurasian desert belt from Sahara through Arabian Peninsula to Thar Desert, with latitude lines marked

The continuous desert belt clearly shows the impact of subtropical high pressure across two continents

Exam traps

Trap: Thinking this belt is caused by distance from ocean - it's primarily atmospheric pressure

Trap: Confusing with cold current deserts like Namib or Atacama - those are coastal, not continental

Trap: Not recognizing the continuous nature - it's one connected climatic phenomenon, not separate deserts

Hadley Cell Circulation

Geography

Hadley Cell: The Engine Behind Subtropical Deserts

Must know

Thermal circulation between equator and 30° latitude

Creates ITCZ (rising air) and subtropical highs (descending air)

Good to know

Drives trade winds and westerlies formation

Named after George Hadley (1735)

Circulation Mechanism

The Hadley Cell is Earth's most important atmospheric circulation pattern, driven by intense solar heating at the equator. This thermal circulation directly creates both the wet equatorial zone and the dry subtropical desert belt.

Complete Hadley Cell Process

%%{init: {"flowchart": {"wrappingWidth": 460}}}%%
flowchart TD
  s1["`**Equatorial Heating**
Intense solar radiation heats surface air`"]
  s2["`**Air Rises (ITCZ)**
Hot air becomes less dense and ascends`"]
  s3["`**Cooling & Condensation**
Rising air cools, water vapor condenses → heavy rainfall`"]
  s4["`**Poleward Flow**
Dry air moves toward 30° latitude at high altitude`"]
  s5["`**Air Descends at 30°**
Cool, dry air sinks creating high pressure`"]
  s6["`**Adiabatic Warming**
Descending air compresses and heats up`"]
  s7["`**Surface Return Flow**
Air flows back to equator as Trade Winds`"]
  s1 --> s2
  s2 --> s3
  s3 --> s4
  s4 --> s5
  s5 --> s6
  s6 --> s7

Hadley Cell Climate Zones

Latitude Zone	Air Movement	Pressure	Climate	Examples
0°-10°	Rising (ITCZ)	Low pressure	Wet, tropical	Amazon, Congo Basin
10°-20°	Descending begins	Transitional	Semi-arid	Sahel, Brazilian Cerrado
20°-30°	Strong descent	High pressure	Desert	Sahara, Arabian, Thar
30°-40°	Lateral flow	Moderate	Mediterranean	California, Mediterranean Sea

Hadley Cell Diagram

The Hadley Cell creates both equatorial rainfall and subtropical deserts through this circulation pattern

Source: Earthguide — AtmosphericCirculation · earthguide.ucsd.edu

Exam traps

Trap: Forgetting that descending air at 30° is the key - not just 'high pressure' in general

Trap: Confusing ITCZ (equatorial low) with subtropical high - they're opposite ends of Hadley Cell

Trap: Not connecting trade winds to Hadley Cell - they're the surface return flow

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