UPSC Prelims 2011 Q94: Geography – Atmosphere & Climatology
What could be the main reason/reasons for 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?
- (a) 1 only
- (b) 2 only
- (c) Both 1 and 2
- (d) Neither 1 nor 2
Answer: (a) 1 only
Explanation
Why the African-Eurasian desert belt formed
This vast desert belt (Sahara through the Middle East to the Thar) follows a specific atmospheric pattern.
| Statement | Verdict | Reason |
|---|---|---|
| 1. Located in sub-tropical high-pressure cells | Correct | These deserts sit under subtropical high-pressure belts (around 20-30° latitude), where descending, dry air suppresses rainfall |
| 2. Under the influence of warm ocean currents | Incorrect | Coastal deserts are more often associated with cold ocean currents (e.g., the Canary Current near the Sahara), which suppress rainfall further, not warm currents |
Desert belt formation:
| Point | Detail |
|---|---|
| Key driver | Subtropical high-pressure cells — descending dry air |
| Coastal deserts | Often reinforced by cold ocean currents, not warm ones |
| Belt location | Roughly 20-30° N/S latitude |
Answer: (a) 1 only.
Why each option is right or wrong
- (a) CORRECT. Subtropical high-pressure cells, with their descending dry air, are the primary driver of this desert belt's formation.
- (b) Incorrect. Coastal deserts in this belt are typically linked to cold, not warm, ocean currents.
- (c) Incorrect. Statement 2's warm-current claim is false, so 'both' cannot be correct.
- (d) Incorrect. Statement 1 is accurate, so 'neither' is wrong.
Key point
The African-Eurasian desert belt forms mainly due to subtropical HIGH-PRESSURE CELLS with descending dry air — coastal stretches of it are reinforced by COLD ocean currents, not warm ones.
Remember
African-Eurasian desert belt: formed by subtropical high-pressure cells (descending dry air); coastal deserts reinforced by COLD currents, not warm.
Common mistakes
- Confusing cold ocean currents (which reinforce coastal deserts) with warm currents.
- Missing the subtropical high-pressure cell mechanism as the primary desert-forming driver.
- Not connecting descending dry air to the suppression of rainfall in this latitude band.
Exam tip
Subtropical deserts = high-pressure cells + descending dry air. Coastal deserts get reinforced by COLD currents, never warm ones.
Sources
- NCERT Class XI Geography — Fundamentals of Physical Geography — World Climate and Climate Change
- Savindra Singh — Climatology (Prayag Pustak Bhawan)