Water in the Desert


by Richard Mushorn, June 2012

The average annual rainfall in the Sonoran Desert is 6-8 inches.  This does not seem like much, especially when you consider there are places in theU.S.that can receive up to two feet per day.  The mountain regions of Kauai, for example, average 460 inches per year.

Desert rainfall, while certainly much less, is still impressive.  One inch of rain per acre will produce 27,000 gallons of water.  An average annual rainfall of six inches will produce 162,000 gallons of water per acre.  During that year, rain on 6,000 sq ft of rooftop and hardscape (eg, asphalt, brick, concrete) would amount to 21,600 gallons.  This water will then drain onto the desert and increase the water supply from 3.71 gallons per square foot in the undeveloped desert to 4.31 gallons per square foot on developed land.  Add to this the runoff from paved roads, landscape irrigation, car washing, pool drainage, and general water hosing and it is easy to understand that we no longer have a “native” desert landscape, but one that has been altered by building and lifestyles.

The result of this is evident in the overgrown nature of our plants at the road edges.  Depending on the road pitch and drainage we may be attaining multiples of the annual rainfall.  Thus, the desert has, in some ways, become a jungle.  Everyone understands that the National Forest Service thins out our forests to prevent the spread of wildfires.  On a smaller but no less important scale, we as homeowners need to be diligent about our landscape culling efforts to adhere to fire safety as well as aesthetic standards.

The undisturbed naturalSonoranDesertis a beautiful sight.  The plants do not overgrow, nor do they crowd each other.  Without raking and blowing or other human interference the wildflowers will bloom, die, and return on an annual basis.  The plants live synergistically, offering mutual support and adequate space.

If we as neighbors truly wish to live in a natural desert environment we will need to assist Mother Nature by correcting some of the problems we have created.  Although the City of Scottsdale currently does not impose water restrictions, we can reduce or eliminate raking and blowing which stirs seeds to perpetuate growth of grasses and noxious weeds.  Restoring the desert to its native state is not entirely possible but with small compromises we can attain a more natural neighborhood landscape.

The City of Scottsdale has many programs to help you save water.

HVR1 Precipitation Records: 1993-2010