Impact of Climate Change and Land Use on the Southwestern United States

Human impacts on the landscape

This page is a discussion of
Urban Land Use Change in the Las Vegas Valley

Las Vegas images

A comment by Laura R. Musacchio

The images of the growth of Las Vegas are great.  It is
so difficult for people to visualize the impacts of
development over several generations. These images fill
an important gap -- visually persuasive images that can
change how people see the world. I encourage the authors
of this paper to create more image sequences for  major
metropolitan areas of the West.  Phoenix would be a good
candidate because it is so decentralized.

Urban geologic mapping

A comment by Scott Lundstrom

As part of the Las Vegas Area Urban Corridor Project, I am
mapping the Quaternary geology of the Las Vegas 1:100,000
sheet, which essentially provides a record of  geomorphic
and hydrologic response to past climate change, and
documents surficial soil and deposit distribution prior to
urbanization.  It is good to see the digitized record of
urban growth reported by Acevedo et al, and Sayler -
analyses that combine such data with our digitized
geologic mapping will be able to address many issues
related to the urban impact on the landscape.

One example is flood hazard.  Where areas of alluvial
fans, eolian deposits, and past groundwater discharge
deposits that the dominate the surficial cover of the Las
Vegas Valley are covered by housing developments, the
infiltration characteristics of the surface are changed.
Infiltration is generally reduced and runoff increases
because pavement and rooftops generally have no
infiltration capacity.  In contrast, the fine-sand-
dominated eolian veneer on Quaternary deposits has a
greater infiltration capacity, but one which varies with
its depth and somewhat inversely with the amount of soil
caliche development related to the age and geologic
history of the underlying surficial materials, as
documented by geologic mapping.  Thus the spatially
varying change in infiltration and runoff potential for
specified precipitation scenarios can be evaluated to
address the change in flood hazards with urbanization.
This real effect was illustrated in November, 1996, when a
relatively minor regional rainfall event of about 2 cm
over 3 hours produced disruptive flooding in central urban
areas of Las Vegas.  In contrast, no evidence of runoff
was observed in any of the natural channels of not-yet-
urbanized alluvial fans draining higher areas that likely
received greater orographically enhanced rainfall.  On the
other hand, documentation of enhanced runoff through
analysis of both urban mapping and surficial geology might
potentially increase water supply to the urban area by
documenting increased recharge back into the Colorado

Scott Lundstrom
National Cooperative Geologic Mapping
U.S. Geological Survey
Denver, CO

Impacts of urbanization

A comment by Laura R. Musacchio

Questions raised by Scott's good comment:

I am a landscape planner/landscape ecologist, so my thoughts
are reflective of my background.

It is very plausible the increased amount of impervious
pavement in Las Vegas could enhance runoff (and recharge)
into the Colorado River and provide more water for Las
Vegas.  However, the decreased infiltration of water into
the city's soils may also prevent adequate recharge of an
aquifer which is below the city (if there is one to begin
with, my knowledge is limited.).  Or perhaps with all the
lawn watering, there is plenty of ground water recharge? The
most difficult aspect of these highly-urbanized ecosystems
in an the desert is predicting how they will behave given
different natural or human pertubations. We have only begun
to scratch the surface of understanding the dynamics of
these systems.  I do not think these desert cities have been
around long enough for
us to have seen all the dynamics of these systems (however,
the fate of the Anazazi pueblos may be a good place to
start).  My guess is that they will behave as non-linear systems.

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