Previous Year Question
What could be the main reason/reasons for the formation of African and Eurasian desert belt?
It is located in the sub-tropical high pressure cells.
It is under the influence of warm ocean currents.
Which of the statements given above is/are correct?
Correct Answer: A
Detailed Solution
Statement 1 is correct: A large part of the African and Eurasian desert belt lies approximately between 20° and 30° N latitudes. It includes the Sahara, Arabian and Iranian desert regions and is associated with the subtropical high-pressure belt.
The process operates as follows:
Warm air rises in the equatorial region.
In the upper atmosphere, this air moves towards the subtropical latitudes.
Near 30° latitude, the air descends.
While descending into higher pressure, the air is compressed and warms adiabatically.
This warming lowers relative humidity and suppresses condensation and cloud formation.
Consequently, rainfall remains very low and desert conditions develop.
Statement 2 is incorrect: Warm ocean currents generally warm the air and increase evaporation and moisture availability. Coastal currents associated with desert conditions are usually cold ocean currents. For example, the cold Canary Current strengthens aridity along the north-western coast of Africa.
Although cold currents assist the formation of some coastal deserts, the principal large-scale cause of the African and Eurasian desert belt is the subtropical high-pressure system and its descending dry air.