Why do the major deserts of the world occur around 25 degrees N or S?
The major deserts of the world occur around 25 degrees N or S because the Subtropical High Pressure Systems are located there. Air in the Subtropical High Pressure Systems is subsiding and warming. As a result, very little condensation occurs and any liquid water in the atmosphere evaporates. Therefore, clouds and precipitation are rare. Rivers do flow through some deserts, but they get their water from locations outside the desert. Much of the tropical desert region (especially in Africa) has few mountains, so their effect in blocking moist air is minimal.
