Average annual rainfall for Phoenix is about 9 inches. This year we might hit 10 inches. No records this year except in TV drama land.
An extra inch of rain means another four weeks of too wet to drywash. That means less gold per year not more.
We have a few members here that have gold producing claims with occasional running water. Maybe ask them how difficult it is to find gold and water in the same place around Phoenix.
If you are really hung up on the idea of sluicing and panning you can always drive a few hours north and get your toes wet at the public panning area on Lynx or Rose creeks in Prescott. Might be a bit cold and there is no guarantee there will be surface water but you will be able to get your pan wet with a little digging.
Wet season in Arizona is mid July to mid September. If you are crazy enough to stand in a wash when it's raining you might see enough water to float your sluice, car, tent and pan but that wash will be dry a few hours later.
Heavy Pans