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  3. When It Comes to Water, We are All Maya Now It’s possible that the impressive Maya civilization—with mastery of mathematics,

When It Comes to Water, We are All Maya Now It’s possible that the impressive Maya civilization—with mastery of mathematics,

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问题                 When It Comes to Water, We are All Maya Now
    It’s possible that the impressive Maya civilization—with mastery of mathematics, farming, water management, pyramid building and city planning— was undone by summer rain.
    Not enough summer rain.
    Undone, in fact, by exactly the kind of rainfall changes, we ourselves are starting to experience— small shifts in rainfall that persist, and end up having an outsized impact.
    The Maya dominated the Yucatan Peninsula for 600 years, and their settlement and civilization there spanned more than 1,000 years. And yet the great Maya cities collapsed and were abandoned to the jungle over a period of between 100 and 200 years.
    What happened is the subject of wide scholarly debates—although drought (干旱) has often been argued as the major source of the Mayas’ termination, a long-lasting and damaging drought.
    The debates have lacked hard data, until last week.
    In the journal Science, we’ve now got a graph showing the rainfall over the Yucatan, during the last 200 years of Maya dominance—from the year 800 to the year 1000.
    Actually, it’s not quite a graph of rainfall: It’s a graph of each year’s difference from the typical rainfall.
    The years 810 to 815 were pretty wet—10 percent more rainfall than usual. The years 820 to 840 were harsh—not a single year of even average rainfall, and decades of years with 30 percent less rainfall than usual.
    What’s so striking is that the periods of drought were relatively short, often broken by brief good rain, and the actual fall-off in rainfall seems relatively modest—20 to 40 percent less than usual in the dry periods. In fact, over a period of 200 years, there are only a couple deep troughs (波谷) reaching to 40 percent less than usual.
    Could the Mayas have been undone by that kind of shift in rainfall over 100 or 150 years?
    We think the disastrous collapse of a civilization requires an equally disastrous cause. But what if our expectation of water availability is so fixed that we lose track of it? What if small shifts in rainfall can have a surprisingly dramatic impact?
    " Perhaps," write the paper’s authors, " the impact of these droughts was rather modest despite the large associated environmental and societal disruptions. "
    The detailed picture of Maya rainfall is the work of two climate scientists, Martin Medina-Elizalde and Eelco Rohling, and they analyzed lakebed substances that revealed the rainfall. Their conclusions are remarkably detailed—Medina-Elizalde and Rohling were able to tease out the difference between the rainy season rainfall of the summers and the drier season rainfall of the winters. They found that it was the summer rainfall that fell off—and that much of the fall-off may have been due to fewer hurricanes (飓风), or hurricanes of reduced intensity.
    We tend to be pretty confident in our ability to see and measure what’s going on around us, to understand it, and to adjust.
    It’s not certain what happened to the Maya—but one thing is true: They had sophisticated systems for accessing groundwater and for collecting, storing, and distributing rainwater. Like our own systems, the Maya systems were elaborate and fixed in place. When the rain failed to appear in the quantities they had become used to, they didn’t have the flexibility to adapt their water system to serve the millions of people who relied on it.
    They had built a civilization assuming a certain quantity of water, and when 20 or 30 percent less water appeared consistently, their entire way of life, perhaps especially food cultivation, became unsustainable.
    The authors themselves note, somewhat dryly, that the variations in rainfall they found during the period when Maya civilization disintegrated " are not far outside the range of those preceding this time interval, when the Maya civilization flourished. " That is, the amount of rain, and the variation in that rain, wasn’t too different between dominance and destruction.
    Here’s the amazing thing. We’re not actually much better off than the Mayas—except for having a wealth of data to track our own vulnerability.
    Last year, rainfall in Houston, Texas, was 55 percent less than usual. How will Houston get along if that persists for a couple years?
    And then there’s the story of Perth, Australia. Perth is the first western city to confront the possibility of truly running out of water.
    The circumstance in Perth in 2012 is startlingly similar to that in the Yucatan Peninsula in 912.
    Perth has seen average rainfall drop 20 percent over the last 25 years. Water collected by its reservoirs fell by 75 percent over that same period.
    Why?
    Because the reservoirs were built assuming a certain amount and location of rainfall. As one Perth official put it, "All of a sudden, it looked like we’d built our reservoirs in the wrong place. "
For a chilling bar graph of what it looks like when a city looks water disaster in the eye, nothing matches the simple chart Perth’s water utility has put up online.
    The crisis Perth confronted in the late 1990s, and avoided, was identical to that faced by Maya water managers—except Perth got the leadership and vision to fix its water problems.
    Most super-sized modern cities would be in a similar crisis if their long-term water availability suddenly dropped 20 percent—not to say 30 or 40 percent. Our city water systems have no better adaptability than those of the Maya. Indeed, during the cruel 10-year drought in Australia, many big reservoirs were down to 30 or 20 or 10 percent capacity—there is nothing more threatening than a city-sized reservoir that is 80 percent empty.
    The lesson of the Maya and the lesson of Perth are the same. Our water assumptions are just that: assumptions. We should be building city water cultures that have flexibility, multiple sources, the ability to re-use water, the ability to conserve.
    Real strategic thinking about water isn’t about a new water treatment plant, or a plan to replace aging water mains. It’s about knowing what you’ll do if you’re suddenly faced with a 10 or 20 percent loss of available water, permanently.
    Being ready for that kind of shift would change how we all think about water—from factory managers to dads doing the dishes.
    In fact, we are all Maya.
According to the author, our knowledge and understanding about water are just______
选项
答案assumptions
解析 assumption意为“假定，设想”，our water assumptions特指我们对水持有的一些看法或者认知；我们曾经或许以为这都是可靠的认知，但在玛雅的案例面前，这也仅仅是我们的猜想。题干与定位句句型相同，但是定位句中为了表示强调，用了that：assumptions的形式，由于题干中未提到assumptions这个词，则在答案中要省略that，放答案为assumptions。
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