Water in the Desert

Rainfall is not completely absent in desert areas, but it is highly variable. An annualrainfall of four inches is often used to define the limits of a desert. The impact of rainfall upon the surface water and groundwater resources of the desert is greatly influenced by landforms. Flats and depressions where water can collect are common features, but they make up only a small part of the landscape.

Arid lands, surprisingly, contain some of the world's largest river systems, such as the Murray-Darling in Australia, the Rio Grande in North America, the Indus in Asia, and the Nile in Africa. These rivers and river systems are known as "exogenous" because their sources lie outside the aridzone. They are vital for sustaining life in some of the driest parts of the world. For centuries, the annual floods of the Nile, Tigris, and Euphrates, for example, have brought fertile silts and water to the inhabitants of their lower valleys. Today, river discharges are increasingly controlled by human intervention, creating a need for international river-basin agreements. The filling of the Ataturk and other dams in Turkey has drastically reduced flows in the Euphrates, with potentially serious consequences for Syria and Iraq.

The flow of exogenous rivers varies with the season. The desert sections of long rivers respond several months after rain has fallen outside the desert, so that peak flows may be in the dry season. This is useful for irrigation, but the high temperatures, low humidities, and different day lengths of the dry season, compared to the normal growing season, can present difficulties with some crops.

Regularly flowing rivers and streams that originatewithinarid lands are known as "endogenous." These are generally fed by groundwater springs, and many issue from limestone massifs, such as the Atlas Mountains in Morocco. Basaltic rocks also support springs, notably at the Jabal Al-Arab on the Jordan-Syria border. Endogenous rivers often do not reach the sea but drain into inland basins, where the water evaporates or is lost in the ground. Most desert streambeds are normally dry, but they occasionally receive large flows of water and sediment.

Deserts contain large amounts of groundwater when compared to the amounts they hold in surface stores such as lakes and rivers. But only a small fraction of groundwater enters the hydrological cycle-feeding the flows of streams, maintaining lake levels, and being recharged (or refilled) through surface flows and rainwater. In recent years, groundwater has become an increasingly important source of freshwater for desertdwellers. The United Nations Environment Program and the World Bank have funded attempts to survey the groundwater resources of arid lands and to develop appropriate extraction techniques. Such programs are much needed because in many arid lands there is only a vague idea of the extent of groundwater resources. It is known, however, that the distribution of groundwater is uneven, and that much of it lies at great depths.

Groundwater is stored in the pore spaces and joints of rocks and unconsolidated (unsolidified) sediments or in the openings widened throughfractures and weathering. The water-saturated rock or sediment is known as an "aquifer". Because they are porous, sedimentary rocks, such as sandstones and conglomerates, are important potential sources of groundwater. Large quantities of water may also be stored in limestones when joints and cracks have been enlarged to form cavities. Most limestone and sandstone aquifers are deep and extensive but may contain groundwaters that are not being recharged. Most shallow aquifers in sand and gravel deposits produce lower yields, but they can be rapidly recharged. Some deep aquifers are known as "fossil waters. The term "fossil" describes water that has been present for several thousand years. These aquifers became saturated more than 10,000 years ago and are no longer being recharged.

Water does not remainimmobile in an aquifer but can seep out at springs or leak into other aquifers. The rate of movement may be very slow: in the Indus plain, the movement of saline (salty) groundwaters has still not reached equilibrium after 70 years of being tapped. The mineralcontent of groundwaternormally increases with the depth, but even quite shallow aquifers can be highly saline.

Which of the following statements about annual rainfall can be inferred from paragraph 1?

A. Flat desert areas receive more annual rainfall than desert areas with mountains.

B. Areas that receive more than four inches of rain per year are not considered deserts.

C. Many areas receive less than four inches of annual rainfall, but only a few are deserts.

D. Annual rainfall has no impact on the groundwater resources of desert areas.

B. Positioning to the second sentence with an annual rainfall keyword, said that where the annual rainfall is less than 4 inches is considered to be a desert, it is inferred that the opposite is where the annual rainfall is greater than 4 inches, which is not a desert, that is, B.

The word "drastically" in the passage is closest in meaning to

A. obviously

B. unfortunately

C. rapidly

D. severely

D drastically: thoroughly and fiercely. A is obviously; B is unfortunately; C is fast; D is fiercely. So D's severely correct.

In paragraph 2, why does the author mention the Ataturk and other dams in Turkey?

A. To contrast the Euphrates River with other exogenous rivers

B. To illustrate the technological advances in dam building

C. To argue that dams should not be built on the Euphrates River

D. To support the idea that international river-basin agreements are needed

The purpose of the function, the two details of the sentence is simply to say an example, look forward, that the river flow is more and more controlled by people, making the need for an agreement, so the answer is D, need agreement.

According to paragraph 2, which of the following is true of the Nile River?

A. The Nile's flow in its desert sections is at its lowest during the dry season

B. The Nile's sources are located in one of the most arid zones of the world

C. The Nile's annual floods bring fertile silts and water to its lower valley

D. The Nile's periodic flooding hinders the growth of some crops

C. Use Nile to target the first sentence and the fourth sentence. In the first sentence, the Nile is just an example. So in the fourth sentence, the answer is that the Nile River flooded valleys with water and water, which is exactly the same as C, so the answer is It is C.

The word "dwellers" in the passage is closest in meaning to

A. settlements

B. farmers

C. tribes

D. inhabitants

D dwell: Settled. So dweller is the meaning of the residents. A is settled; B is a peasant; C is a tribe; D is a resident. So D's inhabitants are correct.

Paragraph 5 supports all of the following statements about the groundwater In deserts EXCEPT:

A. The groundwater is consistently found just below the surface

B. A small part of the groundwater helps maintain lake levels

C. Most of the groundwater is not recharged through surface water

D. The groundwater is increasingly used as a source of freshwater

A EXCEPT questions, exclusion. A in the original text does not correspond to, wrong, election; B's lake level keyword positioning to the second sentence, small fraction and small part synonymous replacement, correct, not selected; C surface water and the second sentence of the same surface flow Meaning replace, correct, not selected; D's freshwater keyword positioning to the third sentence, correct, not selected.

The word "fractures" in the passage is closest in meaning to

A. streams

B. cracks

C. storms

D. earthquakes

B fracture: fractures, cracks, cracks. A is a stream; B is a crack; C is a storm; D is an earthquake. So B's crack is correct.

According to paragraph 6, which of the following statements about aquifers in deserts is true?

A. Water from limestone and sandstone aquifers is generally better to drink than water from sand and gravel aquifers

B. Sand and gravel aquifers tend to contain less groundwater than limestone or sandstone aquifers

C. Groundwater in deep aquifers is more likely to be recharged than groundwater in shallow aquifers

D. Sedimentary rocks, because they are porous, are not capable of storing large amounts of groundwater

B. You may need to read more articles using auifer keyword positioning, and use the exclusion method faster. A limestone keyword positioning to the fifth sentence, but this sentence does not say drink thing, so A wrong; B sand and gravel keyword positioning to the penultimate sentence, said the low production of sand and aquifer water , but it's easier to recharge. The first sentence says limestone and sandstone, which means that the high is the two, so B is correct, and C is anti- ; D of the sedimentary rocks do keyword positioning to the third sentence, should be able to store, options Say it wrong, wrong.

According to paragraph 6, the aquifers called fossil waters

A. contain fossils that are thousands of years old

B. took more than 10,000 years to become saturated with water

C. have not gained or lost any water for thousands of years

D. have been collecting water for the past 10,000 years

C. Positioning the word from the fossil waters to the bottom three sentences. The water layer containing fossil water was spontaneously rehydrated as early as a thousand years ago. The answer is C. This sentence was saturated 10,000 years ago, so B's Ten thousand years before it became saturated and D, the water that had gathered for 10,000 years was not right; A was completely indecisive.

The word "immobile" in the passage is closest in meaning to

A. enclosed

B. permanent

C. motionless

D. intact

C immobile: Immovable, unchanging. A is closed; B is permanent; C is incomprehensible; D is complete. So C's motionless is correct.

The passage supports which of the following statements about water in the desert?

A. The most visible forms of water are not the most widespread forms of water in the desert.

B. Groundwater in the desert cannot become a source of drinking water but can be used for irrigation.

C. Most of the water in the desert is contained in shallow aquifers that are being rapidly recharged.

D. Desert areas that lack endogenous or exogenous rivers and streams cannot support life.

A asks the entire passage, so the elimination is best, and you should focus on the beginning of each segment. At the beginning of the fifth paragraph, A's message said that the amount of water in the desert is greater than that of rivers and lakes, while rivers and lakes are the most common forms of water, but not the most, so A is correct; B is wrong, and the third paragraph of the original text Speaking of being able to irrigate, but did not say can not drink, wrong; C's rapid recharged and apparently the sixth paragraph of the fifth sentence is not recharge the contrary; D original did not say.

These sudden floods provide important water supplies but can also be highly destructive..

A

B

C

D

C, the three transition points, are the pronouns, noun water supplies and noun flood, flood is synonymous with the large flows of water in the last sentence of the fourth paragraph of the source text, so B or C may be correct, but these can determine C pairs because Before these floods must be said flood, just in front of large flows of water to meet the requirements.

Select from the seven sentences below, the two sentences that correctly characterize endogenous rivers and the three sentences that correctly characterize exogenous rivers. Drag each sentence you select into the appropriate column of the table. Two of the sentences will NOT be used. This question is worth 3 points.

Exogenous RiversEndogenous Rivers
A.Their water generally comes from groundwater springs.
B.Their water is saltier than the water of most other rivers.
C.They include some of the world's largest rivers.
D.They originate outside the desert.
E.They often drain into inland basins and do not reach the sea.
F.They contain too much silt to be useful for irrigation.
G.Their water flow generally varies with the season of the year.

The second sentence of the second paragraph refers to exogenous, and the fourth paragraph refers to endogenous. The first sentence of the second paragraph refers to the largest river, corresponding to the they include option; the second sentence of the paragraph says that these rivers originate outside the arid zone, corresponding to the they originate option; the beginning of the third paragraph corresponds to their water flow option; These three are exogenous answers; the second and fourth sentences of the fourth paragraph correspond to their water general and they often, respectively. These two are endogenous answers.