process typically further reduces the carrying capacity of an already fragile
environment. Natural fluctuations in rainfall can change the shape of a
desert, usually working around the margins of an existing desert. Overgrazing, mining of groundwater, and overuse in farming are primary human
activities that can produce desertification of an area.
The African Sahel is the most striking example of desertification or land
degradation seen in modern times. The Sahel is the belt that extends across
Africa at about 15° N and forms the southern extent of the Sahara desert.
An increase in the nomadic herding population of the region in combination
with a drought lasting from 1968 to 1991 has produced desertification in
the area (Strahler and Strahler 2000). Desertification has resulted in a
drastic reduction of regional grazing capacity until conditions and time allow
regeneration of the vegetative cover, if erosion and the other impacts of
desertification have not been so severe as to irreversibly damage the land.
Global warming can produce desertification in the same way that natural
climate change does; therefore, accurate climate modeling is a requisite
component of understanding desertification. Simulation models project that
the net effects of global warming and desertification will be an intensification and extension of drought conditions during dry seasons (Feddema
1999).
15.3 Water as a Scarce Resource
Water is a critical resource for life and essential for economic success in a
modern, developed society. Water is required for domestic consumption,
sanitary use, industrial use, cooling water in the generation of electric
power, hydroelectric power generation, and agricultural irrigation. Water
quantity can be measured in terms of total demand but is better represented
in terms of the quantity per person over some period of time (daily or
yearly). During the past century, there was an 800% increase in total water
demand, driven primarily by population increases, but demand per person
also doubled (Gleick 1998).
Models can be used to identify and alleviate water distribution problems.
For example, Jowitt and Xu (1992) found that relatively simple time-series
models can be used to predict consumer water demand and that these
results can be used to design water distribution systems. As another
example, Luijten et al. (2001) used a model to assess water availability and
use under different development pathways of development and growth in
Latin American countries with steep-slope farming. The model helped
reduce the complexities of dealing with the land–water interface and spatial
linkages within the watershed. These model results can help teach local
stakeholders about responses of the landscape to water management
practices. A third example focuses on balancing difference uses of water.
Droogers et al. (2000) developed a simulation model to evaluate irrigation
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Wendell Chris King and Virginia H. Dale
environment. Natural fluctuations in rainfall can change the shape of a
desert, usually working around the margins of an existing desert. Overgrazing, mining of groundwater, and overuse in farming are primary human
activities that can produce desertification of an area.
The African Sahel is the most striking example of desertification or land
degradation seen in modern times. The Sahel is the belt that extends across
Africa at about 15° N and forms the southern extent of the Sahara desert.
An increase in the nomadic herding population of the region in combination
with a drought lasting from 1968 to 1991 has produced desertification in
the area (Strahler and Strahler 2000). Desertification has resulted in a
drastic reduction of regional grazing capacity until conditions and time allow
regeneration of the vegetative cover, if erosion and the other impacts of
desertification have not been so severe as to irreversibly damage the land.
Global warming can produce desertification in the same way that natural
climate change does; therefore, accurate climate modeling is a requisite
component of understanding desertification. Simulation models project that
the net effects of global warming and desertification will be an intensification and extension of drought conditions during dry seasons (Feddema
1999).
15.3 Water as a Scarce Resource
Water is a critical resource for life and essential for economic success in a
modern, developed society. Water is required for domestic consumption,
sanitary use, industrial use, cooling water in the generation of electric
power, hydroelectric power generation, and agricultural irrigation. Water
quantity can be measured in terms of total demand but is better represented
in terms of the quantity per person over some period of time (daily or
yearly). During the past century, there was an 800% increase in total water
demand, driven primarily by population increases, but demand per person
also doubled (Gleick 1998).
Models can be used to identify and alleviate water distribution problems.
For example, Jowitt and Xu (1992) found that relatively simple time-series
models can be used to predict consumer water demand and that these
results can be used to design water distribution systems. As another
example, Luijten et al. (2001) used a model to assess water availability and
use under different development pathways of development and growth in
Latin American countries with steep-slope farming. The model helped
reduce the complexities of dealing with the land–water interface and spatial
linkages within the watershed. These model results can help teach local
stakeholders about responses of the landscape to water management
practices. A third example focuses on balancing difference uses of water.
Droogers et al. (2000) developed a simulation model to evaluate irrigation
298
Wendell Chris King and Virginia H. Dale