Question

why are deserts located on western margins of continents in the tropics?

Answer 1

 In the subtropical regions, easterly winds called Trades blow. They are called North-East Trades in Northern Hemisphere and South-East Trades in Southern Hemisphere. These planetary winds blow from the Sub tropical High pressure belts to the Equatorial Low Pressure Belt. So they blow from higher latitude to lower latitude and hence suffer more evaporation than condensation. So, these winds become onshore and moist in the eastern margins of continents where they provide profuse precipitation. But while they cross the continent to reach the western parts, they become offshore and dry and hence do not provide rainfall. So, deserts have formed in the western margins of continents in the subtropics.