Geoscience Reference
In-Depth Information
influx of people into the region. As a result of the drought, the
SNWA moved the drought status from
drought watch
to
drought
alert
and imposed a series of tougher water restrictions. For ex-
ample, no new grass turf is allowed in residential yards and is
limited in rear and side yards to 50% of the area, with a 3 m (10
ft) minimum dimension and a 464 m
2
(5000 ft
2
) maximum. In
addition, lawn watering is allowed on only three assigned days
per week and golf courses are governed by strict water budgets.
If violations of these and other restrictions are observed, cus-
tomers are first warned, and then subsequently fined if further
waste occurs. As of October 2013, these restrictions are still in
place, and, in fact, the SNWA is now subsidizing people to tear
out their lawns to save water.
Colorado River and local groundwater. Efficiency has indeed
improved dramatically in the recent past, as Las Vegas residents
now stretch their water supplies further through the restrictions
described earlier. Unfortunately, these gains are offset by the
increased overall demand due to growing population. As a re-
sult, a systematic effort is currently ongoing to acquire water
from groundwater supplies in Lincoln and White Pine counties,
which lie north of Las Vegas (Figure 20.5a). The extent of these
supplies is currently being assessed, with the goal of building a
pipeline that will deliver water to Las Vegas in the near future.
Although these counties are lightly populated (~14,000 total
people), many residents are fighting to keep what they consider
to be
their
water. They believe that groundwater extraction from
the counties will degrade the environment and destroy their tra-
ditional ranching lifestyle. They recall the negative impacts that
water diversion from Owens Valley, California, to Los Angeles in
the early 20th century had on the environment. Much of this water
was diverted from Mono Lake, which is about 385 km (240 mi)
northeast of Los Angeles, to fuel the rapid growth of southern
California. As a result of this diversion, the level of Mono Lake
fell about 14 m (45 ft), approximately 7500 hectares (18,500
acres) of shoreline were consequently exposed to blowing wind,
and the salinity of the lake doubled by the early 1980s. The con-
cerns of residents in Lincoln and White Pine counties are shared
by officials in neighboring Utah because groundwater extraction
in Nevada may impact groundwater resources there. They are par-
ticularly concerned about the viability of Fish Springs, which is
a lake that is home to a fish called the least chub. Environmental-
ists are concerned that the least chub will become endangered if
the lake level declines as a result of groundwater extraction in
Nevada. Tapping groundwater resources may also be problem-
atic because it can cause surface subsidence and fracturing. Such
problems have already been identified in Tucson basin in Arizona,
for example, where as much as 13 cm (~5 in.) of subsidence has
occurred in some areas due to compaction of the aquifer system.
A Drought-Prone Future?
In the context of the recent drought, one cannot help but wonder
what future climate conditions may be like in the Southwest.
To answer this question it is useful to look at the past. Recent
tree-ring studies, like those discussed in Chapter 9, indicate that
eight droughts with intensities similar to the current one have
occurred in the region within the past 500 years, with perhaps
two or three being even more severe. These studies show that
arid conditions are the norm and that extreme droughts are fairly
common in the American Southwest. These studies also reveal
that the Colorado River Compact was signed during a relatively
wet phase in the regional climate, one resulting in more runoff
into the Colorado than normal. In other words, the current dis-
tribution of water in the upper basin, lower basin, and Mexico is
based on ideal conditions that may, in fact, be quite rare.
Unfortunately, it appears that ideal climate conditions in
the Southwest may become even more rare in the future. This
assessment is based on climate models that predict future en-
vironmental conditions. These models demonstrate that the
southwestern climate indeed became more arid in the late 20th
century and is continuing the trend into this century. The pre-
vailing belief is that ongoing global climate change is altering
the movement of storms and moisture in the atmosphere and
that the drying trend will continue at least until 2100. In short,
climate researchers are concerned that the drought conditions
of the past decade will become the new norm for the region.
If this assessment of future climate conditions is true, it
has important implications for water resources in southwest-
ern cities such as Las Vegas and Phoenix, especially if recent
growth rates pick up again as the national economy improves.
An increasing number of scientists argue that planners should
acknowledge that water resources are limited and that shortfalls
will occur more frequently in the future. Some even suggest
that recent growth rates are unsustainable and that limits should
actually be placed on the number of people who can live in the
region. In response to these concerns, a 2007 planning study
argued that limiting growth in Clark County was an unrealis-
tic method of drought control because the economy of Nevada
would suffer. Instead, the focus should be to increase the effi-
ciency of water usage and to continue an aggressive search for
other water sources to supplement the current supply from the
KEY CONCEPTS TO REMEMBER ABOUT
LAS VEGAS WATER ISSUES
1.
The Las Vegas Valley lies within the rain shadow of
the Sierra Nevada Mountains and thus receives about
10 cm (4 in.) of precipitation per year. Average annual
temperatures range from warm in the winter to excep-
tionally hot in summer.
2.
A major factor in the growth of Las Vegas was the
Colorado River Compact, which was signed in 1922.
This document legally subdivided the Colorado River
basin into separate basins with distinct water rights.
3.
Rapid growth of Las Vegas began in the 1950s, in part
due to the advent of air conditioning. Population has
grown from about 50,000 in 1950 to over 2 million today.
4.
Increased population has raised serious concerns
about the sustainability of water supplies in the region.
