In what way does the karez in Xinjiang get its water?

Karez is built in the form of an underground canal (the underground part looks a bit like a ditch), which may be because of the weather in Xinjiang. Water will flow along the ditch (to reduce evaporation of water). People drill some wellheads on the ground that are no different from those in other places, and draw water with buckets and wheels like people in other places.