Geoscience Reference
In-Depth Information
Case 2: Soil Salinization in
Arid and Semi-Arid Lands
As a result, water managers in Las Vegas can employ
strict use restrictions and are aggressively searching for
supplemental sources of water from neighboring areas.
5.
Regional climate models suggest that the southwestern
United States will become more drought-prone in the com-
ing decades, potentially making water concerns more acute.
This next case study expands on the theme of human interactions in
marginal lands by focusing on some of the problems that can develop
in association with agriculture in these regions. As we discussed
earlier in this chapter, the development of agriculture increased the
carrying capacity of landscapes and gradually led to increased popu-
lation. During the previous hunter/gatherer phase of human evolu-
tion, the global population was probably less than 5 million people.
Today, modern agricultural techniques support a global population
of about 6.8 billion, with 9 billion (perhaps more) projected by 2050.
The ability of agriculture to feed everyone on a sustain-
able basis poses enormous challenges. The production of cereal
grains such as wheat and sorghum, for example, will have to
double
between now and 2050, not only to meet the basic needs
of so many people, but also because more people will consume
grain-fed beef as their standards of living improve. To meet this
growing demand, further increases in agricultural output are es-
sential for global political and social stability and equity. An
even greater challenge is to meet this demand in a sustainable
way that maintains the health of environmental systems.
One of the primary factors complicating the task of in-
creasing global food production is simply the limited supply
of
arable land
on Earth (Figure 20.10). Recall from the discus-
sion of the hydrological cycle in Chapter 7 that about 71% of
As you can see, a full understanding of population growth
and water use in marginal environments such as the southwest-
ern United States requires a holistic assessment of many factors
directly related to physical geography. This particular case study
has included several topics discussed in earlier chapters, such
as Köppen climates, the Basin and Range province, the rain
shadow effect, groundwater, drainage basins, runoff, and global
climate change. All these factors are intimately related to create
a distinctive environment in the southwestern United States, one
that happens to be the center of a recent population boom.
The societal tensions resulting from issues like this one are
loosely referred to as
water wars
and are particularly intense in
places where different groups of people compete for the same
water supply. According to current estimates, about 1 billion
people on Earth lack access to reliable freshwater supplies. This
number will undoubtedly increase as global population continues
to grow. In many other places, access to water is being used as a
political weapon to influence the behavior of neighboring coun-
tries. An excellent example is Turkey, where dams have been
built across the Tigris and Euphrates rivers that reduce stream
flow into neighboring Iraq. Examples such as these abound
around the world and will be political flashpoints for the rest of
your life. To fully understand them, and their potential solutions,
requires an excellent understanding of physical geography.
Arable land
Land that has the high potential to be cultivated
for crop production.
Hectares per capita
Less than 0.10
0.10- 0.19
0.20- 0.29
0.30- 0.49
0.50 or more
No data
Arable land, 1999-2001
Figure 20.10 Map of global arable lands.
This map shows the countries that contain arable land; it is somewhat misleading. Much
of the western United States, for example, as well as most of Australia, contains very little arable land. Regardless, note that this map
indicates that extensive parts of the world contain few lands suitable for agriculture.
