Answer:
I'll assume you have to match the name with their definitions.
1. aquifers
underground water sources
That's because of the presence of porous rocks that let water pass through them and reach an underground cavern that then acts as a tank.
2. delta
a broad, triangular-shaped land area at the mouth of a river
That's common especially in larger rivers that meet their destination point (usually the ocean).
3. oasis
a small fertile area in the desert, usually a place where water is close to the surface (plural - oases)
We all heard about oases in the desert, where human and animals alike gather to drink.
4. rain shadow
an area that receives less precipitation because of its location on the leeward side of a mountain
That's common in high mountains region where the mountains are so high they block the passage of clouds to the other side.
North Cascades National Park is very rocky and features mountains and sneak peeks of the North Cascades Range. The mountain peaks have formed due to erosion from water and glacial ice.
Enlightment and other things
Answer: Is prone to desertification or drought.
Explanation: The Sahel region is located in Africa between the Sahara to the north and the Sudanian Savanna to the south.
The Sahel has a semi arid climate which is characterized by precipitation below potential evapotranspiration.
What this means is that the amount of water that would be evaporated and transpired by a specific crop or ecosystem is low. This region is prone to desertification or drought because of the low amount of water evaporated and transpirated in the region.