I’ve been to quite a few deserts that get the occasional seasonal torrential rain.

They still remain deserts nine to ten months out of twelve.

The water saturates the soil, can’t percolate to underground aquifers where it could otherwise be stored, and runs into (ephemeral) rivers, washing away some of whatever is left of the soil with it.

I wouldn’t be surprised if two places could have roughly the same yearly amount of precipitation yet look completely different depending on how the rainfalls are distributed over time.