TOEFL Experts Reading Practice 38
Over the past century, the states of Utah, Nevada, New Mexico, Arizona, and California, forming the Southwestern United States, have experienced tremendous population growth. In the 1910 census, these five states accounted for less than 4 percent of the domestic population. In 2010, this figure was greater than 16 percent. Population growth in the Southwest continues to outstrip growth in the rest of the country, as the region receives positive net migration from other states as well as substantial immigration from foreign countries. Part of the appeal is the pleasant weather, with mild to hot temperatures all year, and low precipitation. However, therein lies the crux of a major problem—the ecosystems of the Southwest are not equipped to sustainably provide enough water for the increasing number of people that live there.
All five Southwestern states rely greatly on external water sources, plus groundwater sources, which are large but finite. Per-capita water consumption is also higher than the national average for two reasons. First, these states have a drier climate, so more water is needed for the watering of lawns and gardens. Second, all five states have a substantial farming industry and are exporters of agricultural products domestically and abroad. These states therefore use much more water for irrigation per person than the rest of the United States.
Water use has become much more efficient across the United States in recent decades. Since 1980, per-capita usage has fallen by about 40 percent. This decline is even more pronounced in the Southwest. However, it is counterbalanced by a comparable growth in population, such that the total amount of water being consumed annually in the Southwest is basically unchanged. This level of usage is not sustainable over the long term.
The Southwestern states consumed a total of 61 million acre-feet1 of water in 2010. About 35 percent of this water comes from groundwater, and the rest comes from surface water, such as lakes and streams. Most of the groundwater being used is not fully replenished. In California alone, the net withdrawal of groundwater, after replenishment from precipitation and surface water, is currently around 10 million acre-feet per year. At this rate, California’s known usable groundwater supplies will be exhausted by the year 2060.
For surface water, these five states are heavily reliant on various sources. California has ample native freshwater supplies in the northern and central portions of the state. Excluding California, however, over half of the freshwater needs of the Southwest are met from a single source: the Colorado River. This river originates in the Rocky Mountains and meanders through Utah and Arizona before forming the border of Arizona and Nevada, plus parts of the Arizona–California border. The river then continues into Mexico.
Allocation of rights to this water has been a political flash point among the Southwestern states since the original Colorado River Compact, drafted in 1922. According to the present version of the Compact, 15 million acre-feet per year are allocated to seven Western states, of which the five Southwestern states receive about 10 million—Wyoming and Colorado receive the rest. Mexico also has an annual allotment of 1.5 million acre-feet. The river is dammed at various places, with the Hoover Dam on the border of Arizona and Nevada, forming Lake Mead, being the most well-known.
There are several problems with this allocation. First, the estimates for annual water flow in the Colorado River were based on a survey that occurred during a period of relatively heavy rainfall. It is unlikely that the Colorado River can continue to produce enough water to fill these allocations indefinitely. Evidence of this is seen by the water levels in Lake Mead, which are currently more than 150 feet below peak. Second, the agreement is a zero-sum game: any increase in allocation to one state must necessarily come at the expense of another. This puts pressure on high-growth states like Arizona and Nevada. Finally, there is the problem of the ongoing drought in the region. The drought puts pressure on all water sources, and the Colorado River is no exception. If the drought remains unabated, Lake Mead could eventually become unusable, and hydroelectric generating capacity in the Southwest could fall below minimum requirements as early as the year 2020.
Over the past century, the states of Utah, Nevada, New Mexico, Arizona, and California, forming the Southwestern United States, have experienced tremendous population growth. In the 1910 census, these five states accounted for less than 4 percent of the domestic population. In 2010, this figure was greater than 16 percent. Population growth in the Southwest continues to outstrip growth in the rest of the country, as the region receives positive net migration from other states as well as substantial immigration from foreign countries. Part of the appeal is the pleasant weather, with mild to hot temperatures all year, and low precipitation. However, therein lies the crux of a major problem—the ecosystems of the Southwest are not equipped to sustainably provide enough water for the increasing number of people that live there.
All five Southwestern states rely greatly on external water sources, plus groundwater sources, which are large but finite. Per-capita water consumption is also higher than the national average for two reasons. First, these states have a drier climate, so more water is needed for the watering of lawns and gardens. Second, all five states have a substantial farming industry and are exporters of agricultural products domestically and abroad. These states therefore use much more water for irrigation per person than the rest of the United States.
Water use has become much more efficient across the United States in recent decades. Since 1980, per-capita usage has fallen by about 40 percent. This decline is even more pronounced in the Southwest. However, it is counterbalanced by a comparable growth in population, such that the total amount of water being consumed annually in the Southwest is basically unchanged. This level of usage is not sustainable over the long term.
The Southwestern states consumed a total of 61 million acre-feet1 of water in 2010. About 35 percent of this water comes from groundwater, and the rest comes from surface water, such as lakes and streams. Most of the groundwater being used is not fully replenished. In California alone, the net withdrawal of groundwater, after replenishment from precipitation and surface water, is currently around 10 million acre-feet per year. At this rate, California’s known usable groundwater supplies will be exhausted by the year 2060.
For surface water, these five states are heavily reliant on various sources. California has ample native freshwater supplies in the northern and central portions of the state. Excluding California, however, over half of the freshwater needs of the Southwest are met from a single source: the Colorado River. This river originates in the Rocky Mountains and meanders through Utah and Arizona before forming the border of Arizona and Nevada, plus parts of the Arizona–California border. The river then continues into Mexico.
Allocation of rights to this water has been a political flash point among the Southwestern states since the original Colorado River Compact, drafted in 1922. According to the present version of the Compact, 15 million acre-feet per year are allocated to seven Western states, of which the five Southwestern states receive about 10 million—Wyoming and Colorado receive the rest. Mexico also has an annual allotment of 1.5 million acre-feet. The river is dammed at various places, with the Hoover Dam on the border of Arizona and Nevada, forming Lake Mead, being the most well-known.
There are several problems with this allocation. First, the estimates for annual water flow in the Colorado River were based on a survey that occurred during a period of relatively heavy rainfall. It is unlikely that the Colorado River can continue to produce enough water to fill these allocations indefinitely. Evidence of this is seen by the water levels in Lake Mead, which are currently more than 150 feet below peak. Second, the agreement is a zero-sum game: any increase in allocation to one state must necessarily come at the expense of another. This puts pressure on high-growth states like Arizona and Nevada. Finally, there is the problem of the ongoing drought in the region. The drought puts pressure on all water sources, and the Colorado River is no exception. If the drought remains unabated, Lake Mead could eventually become unusable, and hydroelectric generating capacity in the Southwest could fall below minimum requirements as early as the year 2020.
→(P3) Water use has become much more efficient across the United States in recent decades. Since 1980, per-capita usage has fallen by about 40 percent. This decline is even more pronounced in the Southwest. However, it is counterbalanced by a comparable growth in population, such that the total amount of water being consumed annually in the Southwest is basically unchanged. This level of usage is not sustainable over the long term.
→(P3) Water use has become much more efficient across the United States in recent decades. Since 1980, per-capita usage has fallen by about 40 percent. This decline is even more pronounced in the Southwest. However, it is counterbalanced by a comparable growth in population, such that the total amount of water being consumed annually in the Southwest is basically unchanged. This level of usage is not sustainable over the long term.
→(P3) Water use has become much more efficient across the United States in recent decades. Since 1980, per-capita usage has fallen by about 40 percent. This decline is even more pronounced in the Southwest. However, it is counterbalanced by a comparable growth in population, such that the total amount of water being consumed annually in the Southwest is basically unchanged. This level of usage is not sustainable over the long term.
- The immense population growth enjoyed by the states of the Southwestern United States has stressed water resources in the region.