What could be the main reason/reasons for the formation

Solution

The natural zones in the tropical belts of the northern and southern hemispheres are deserts. These zones lie in the interior and along the western coasts of most continents.  Subtropical deserts They are caused by the circulation patterns of air masses. They are found along the Tropic of Cancer, between 15 and 30 degrees north of the Equator, or along the Tropic of Capricorn, between 15 and 30 degrees south of the Equator. As the hot air rises, it cools and drops its moisture as heavy tropical rains. The resulting cooler,drier air mass moves away from the Equator. As it approaches the tropics, the air descends and warms up again.  The descending air hinders the formation of clouds, so very little rain falls on the land below. Around 30° N. and S., the poleward flowing air begins to descend toward the surface in subtropical high-pressure belts. Since the African and Eurasian desert belt lies in the sub-tropics, Hence, statement 1 is correct. Desert zones in tropical regions have a highly diverse relief, shaped by physical weathering and eolian accumulation. In the aridest deserts (Sahara, Arabian), vast gravelly, sandy, stony, and saline expanses are almost completely devoid of vegetation, which is concentrated along the intermittent streams and in the foothills of mountain ranges. Cold ocean currents have a direct effect on desert formation in west coast regions of the tropical and subtropical continents. Hence, statement 2 is not correct.