The Sonoran Plain has large dry river beds not unlike the NSW western plains. The largest of these is the Gila River which runs through the West Valley of Phoenix. It is a wide stretch of trees, shrubs, rocks and sand which presumably carries the water out of the city when the monsoons hit.*
The temperatures in Phoenix for the last two weeks have been in the 40C to 46C mark; hot enough that it was 38C the other day and people wore jeans to work instead of shorts. Phoenix is similar to Sydney in so many respects it is uncanny.
I have not yet been through a monsoon season in the desert, but apparently the start of the monsoon is when storms come through throwing lightning but not water. Again remarkably like the August storms western Sydney would get that would cause bush fires by carrying lightning but no water.
However I remember in the Hawkesbury that the flood season was normally easter, not August. That month was better known for its dry storms and buffeting winds.
* Confirmed. The rivers apparently swelled during the monsoon season. Not as much as they used to as the cities have been damming the rivers such as Tempe lake which is a dam in downtown Tempe.
