Why do some islands have regions that receive large amounts of rain annually and other regions of the same island have desert like conditions

The reasons for such big climate differences on the same island are topography, shape, and size of the island, wind patterns, and ocean currents.

Explanation:

While many islands around the world tend to have the same climate conditions across all of their territory, there are some that stick out by having total contrasts from one to the other side. A good example of such an island is Madagascar, where one side of the is covered with tropical rainforest, while the other is desert and semi-desert.

Such things occur because of numerous reasons, such as topography, size and shape of the island, wind patterns, and ocean currents. Since we took Madagascar as an example, we can continue with it. It is an island that has an elongated shape in a roughly north-south direction. The central part is dominated by mountains in a north-south direction, while the western and eastern parts are lowlands. The wind generally blows from the northeastern and northwestern directions.

This leads to a situation where the winds and the humidity they bring are blocked by the mountains, so there is intense rainfall on the windward sides, but very little precipitation on the leeward sides. The windward side thus has lush vegetation while the leeward has most barren land and the occasional desert plant here and there.