Why no reflections in the water? Everything else looks really nice, I like how those rocks/wooden stumps? add a storytelling element, makes me wonder whether they've also once been like the one in the middle.
Even if I had all the water I needed this would be the most thrilling sight in any desert. The surviving grassy terraces look fantastic, especially with the lovely old-school (ginkgo?) trees hanging off the edges and especially crowning the top. Then there's the gorgeous evening sky, the waning crescent, and the great light play over the swirling sands. (The shading does a nice job of the contours but the ripples are a great addition.) Clouds and blowing sand add more atmosphere too.
The little trees trying to grow around it do remind me that it's still a tough place to grow, never mind thrive. Still, all those birds must appreciate the shade and cool water this place provides. Even your special bird seems very happy to visit.
so neat! it makes me think of that layered island in wind waker, you had to latch on to the trees to get to the top, and it had a river falling right into the ocean but i always loved the atmosphere of oases, so this is great!