Arizona is home to both regional and flash floods.  While regional floods can involve large and small river systems, it is Arizona’s perennial rivers – the Colorado, Salt, Gila and Verde Rivers – that are most heavily impacted. 

Arizona’s monsoon season, with its predilection for sudden, torrential and localized rainfall, coupled with a landscape incised by thousands of washes and gullies, is ripe for dangerous flash floods. Of particular concern from a floodplain-management perspective is flooding on alluvial fans, where channels diverge downstream and broad areas outside of channels may be inundated in large floods.