Rain? In the Desert?

The same series of storms that passed through California is in process of making its way through Arizona. We've collected considerable amount of water in the back yard over the past several days. It always accumulates in the low areas because the ground is so hard. It takes a long time for the water to soak into the ground. Some of the computer models show as much as six inches dumping on Phoenix. It seems like s decent storm for anywhere, but to put it into perspective, we only get an average of seven inches of rain a year.