Geologic, Hydrologic, and Urban Hazards for Design in Desert Environments - Design with the Desert: Conservation and Sustainable Development - page 112

suppressed to minimize destruction of property. Over time, the increase of development
along the wildland-urban interface has increased the hazard for fires and the potential
loss of lives and property. In 2011, Arizona and New Mexico experienced the largest and
most severe wildfires in their long histories with wildlands, resulting in the loss of many
homes, destruction of property, and increase in flood hazards, both in forested areas and
former desert grassland.* Effective interventions are urgently needed around many homes
and communities to avoid catastrophic losses in populated areas of the Southwest; oth-
erwise, fires of equal or greater magnitude can be expected in the future. Design on the
urban-wildland interface must address questions of fire safety for new developments and
retrofitting of existing ones to minimize this hazard.
5.8 Summary
Urban design and planning require knowledge of the myriad hydrologic and geologic
hazards posed by the desert environment, how these hazards are posed spatially, and
the concept of acceptable risk. The desert hydrologic environment provides an excellent
example. River channels, surface water, and groundwater are integral to the desert
landscape, on the one hand representing a natural wildness and on the other a resource
to be tamed and used. High variability of precipitation and surface runoff is one strong
characteristic of arid regions; some flood records display nonstationarity with less
predictable flood characteristics and uncertain levels of risk. Both mass wasting and more
common storm runoff can lead to long-term sedimentation problems that can exasperate
flood hazard by defeating engineered channels. Riparian vegetation, desirable in the
urban environment, uses considerable water for growth and can exacerbate sedimentation
in channels, leading to tradeoffs between hazard mitigation and aesthetics.
Other hazards may be more predictable or understandable, particularly within their
context of causality. Overdraft of groundwater systems has caused substantial subsid-
ence in the large alluvial basins of the region that affects buildings and infrastructure.
This hazard is not expected in areas without substantial groundwater extraction or out-
side of large alluvial basins. Seismic hazards are localized in the southwestern United
States along existing fault zones in predictable areas. While earthquake prediction is in
its infancy, knowledge of the hazard is well developed, and this hazard can be mitigated
using existing building codes with acceptable risk.
Few areas of the arid Southwest are subject to all these natural hazards simultaneously,
but Palm Springs, California, provides one example of an urban environment that faces
all of them. The San Andreas fault passes north and east of town, making this urban
center subject to extreme seismic hazards. Drainages from Mount San Jacinto to the west
periodically produce debris flows, and the White Water River, which flows through town,
can produce large floods from rainfall and(or) snowmelt from both the San Jacinto and
San Gorgonio Mountains. Finally, excessive groundwater development in the Coachella
Valley, particularly south and east of town, has caused significant subsidence. Urban
design in an area such as Palm Springs would benefit from multihazard risk assessment
* http://www.azcentral.com/news/articles/2011/07/09/20110709arizona-fire-wallow-fire-100-percent-
contained.html (accessed July 13, 2011).