雅思阅读 195: The River That Ran on Paper — The Colorado's Vanishing Flow（纸上的河流：科罗拉多河的消逝）

改编自 Science / USGS / Western Water（2025-2026年）。雅思阅读 Section 3 难度，约 1050 词。 素材来源：https://www.science.org/content/article/halted-dam-releases-threaten-colorado-river-ecosystems

Reading Passage

A. In the summer of 2026, Lake Mead reached a point that planners a century ago never imagined it could reach. The reservoir behind Hoover Dam, the largest in the United States, slipped to a level roughly 27 per cent of the capacity it was designed to hold — a shoreline marked by a pale, bleached "bathtub ring" of rock left high and dry where the water once lapped, a mineral stain telling anyone who looks exactly how far the water has retreated. It was last filled in 1983 and has declined almost without interruption ever since, a fall so steady that docks, marinas and pump intakes have had to be rebuilt repeatedly to reach water that keeps moving away. The fall is not the story of one bad year but of a decades-long retreat, and it lays bare a quiet contradiction at the heart of the American Southwest: the river on which thirty million people and several major cities depend was shared out on paper during unusually wet years, and the promises made then have outlived the climate that made them plausible. Phoenix, Los Angeles, Denver and cities across four states built their modern growth on that inherited promise, planted lawns and filled swimming pools as if the wet years would never end. They are now having to unlearn that assumption.

B. To understand what is draining the basin, scientists look first to the mountains where the water is born. The Colorado is, in effect, a snow river. Most of its flow begins as winter snowfall high in the Rocky Mountains, which slowly melts through spring and feeds the streams that fill the great reservoirs in a dependable annual rhythm that farmers and cities learned to plan around. In recent years that snowpack has repeatedly fallen to record lows, and the snow that does fall now melts weeks earlier than it did half a century ago, partly because spring warmth arrives sooner. Warm air also demands more moisture from everything it touches, accelerating evaporation from soil and open water. The result is a river that thins early in the season and runs low by summer, before the irrigation season is properly over. Climate records drawn from tree rings and lake sediments show that the drought gripping the region since roughly 2000 ranks among the driest periods in more than a millennium — a megadrought deepened, experts calculate, by the steady warming of the planet rather than by natural fluctuation alone.

C. Yet warming is only half the explanation. The other half is arithmetic. When the basin's states negotiated their shares of the river in the early twentieth century, they divided an annual flow of around 15 million acre-feet — a figure based on a short stretch of unusually wet years that, with hindsight, no longer looks typical, and that was never a reliable long-term average. Since 2000, hotter and drier conditions combined with heavy use have pushed the real average down to roughly 12.5 million acre-feet a year. Demand, in other words, has been written against a water supply that no longer exists. Agriculture, cities and reservoirs have each drawn their share from a tap that runs short, and nobody's allocation has been automatically reduced when the river came up lacking. Engineers call this a structural deficit: the gap is not caused by a single dry season but built into the contract itself, and it cannot be closed by waiting for rain. The accounting error, made in good faith by people who had no reason to distrust the wet years they measured, now structures every water decision the basin must make.

D. For years the giant reservoirs acted as a buffer against exactly this gap, storing fat years to tide over lean ones and giving managers the confidence to keep releasing water even in dry summers. That buffer is now wearing thin. Across the basin, the combined storage has fallen to roughly a third of capacity, and even the emergency supply kept in upper tributaries such as Blue Mesa Reservoir sits at about a quarter of its design volume. A stark sign came in 2026: for only the third time this century, the system failed to refill at all during the spring snowmelt — neither Lake Powell, upstream, nor Lake Mead recovered a single unit of storage. With so little reserve left, managers were forced to slow or halt dam releases that had been scheduled to keep downstream ecosystems and fishing grounds alive, leaving stretches of the riverbed dry for the first time in living memory. The buffer, once taken for granted, has become the very thing in dispute.

E. What happens next is as much a question of governance as of hydrology. The easy answer — build more dams, pump more groundwater, pipe water across deserts — has largely run its course, and the remaining choices are harder: farmers fallowing fields, cities pricing water so that waste costs something, and states renegotiating the shares originally promised to them. Such choices pit neighbours against one another and rural agriculture against urban growth, which is why they are so often postponed until the water is nearly gone. The Colorado case is studied worldwide because it is early: many regions will, in a warmer world, face the same collision between a promise written on paper and a river that no longer delivers. Whether the Southwest adapts through savings, new agreements or painful shortages will tell other drying regions what to expect. The river has not vanished, but the assumptions that once sustained it have. Those who built their lives on the old flow must now build them on the smaller one, and the shift is reshaping everything from agriculture to landscaping.

Questions 1-4

Choose the correct heading for paragraphs B, C, D and E from the list of headings below.

List of Headings i. Why the mountains are delivering less snow ii. How Lake Mead got its name iii. The arithmetic gap between promises and flow iv. When the reservoirs stopped refilling v. Lessons for a warming world vi. The cost of building new dams vii. History of Hoover Dam

1. Paragraph B: ____
2. Paragraph C: ____
3. Paragraph D: ____
4. Paragraph E: ____

Questions 5-8

Choose the correct letter, A, B, C or D.

5. What does the "bathtub ring" around Lake Mead indicate? A. A recent flood has raised the level. B. The water level has fallen far below its former shoreline. C. The reservoir is being restocked with fish. D. A new concrete barrier has been built.

6. According to the passage, why does the river run low earlier in the year? A. Snow melts too slowly in the cold. B. Low snowpack and earlier melt, together with higher evaporation. C. Dams are now kept permanently closed. D. Rainfall has replaced snowfall entirely.

7. The "structural deficit" described in paragraph C refers to A. a single unusually dry season in 2026. B. demand written against a water supply that no longer exists. C. a shortage of engineers to operate the dams. D. leaks in the reservoir walls.

8. What happened in the 2026 snowmelt season? A. The reservoirs reached their highest level ever. B. Neither Lake Powell nor Lake Mead recovered any storage. C. All emergency releases were increased. D. Snowpack was the highest on record.

Questions 9-13

Do the following statements agree with the claims of the writer?

Write:

• TRUE if the statement agrees with the information
• FALSE if the statement contradicts the information
• NOT GIVEN if there is no information on this

9. Lake Mead was last filled in 1983.
10. The drought since 2000 is the wettest period in the region's recorded history.
11. The original agreement allocated roughly 15 million acre-feet per year.
12. Blue Mesa Reservoir currently holds about a quarter of its design volume.
13. The Colorado River basin currently supplies most of Mexico's drinking water.

Questions 14-15

Complete the summary below using NO MORE THAN TWO WORDS from the passage.

The Colorado is essentially a (14) __________ river, and the recent shortfall arises because demand has been set against a flow that is now lower than the figure on which the original (15) __________ were based.

答案与解析

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