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.