環(huán)球英語 Sinking Cities
Welcome to Spotlight. I’m Robin Basselin.
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And I’m Ryan Geertsma. Spotlight uses a special English method of broadcasting. It is easier for people to understand, no matter where in the world they live.
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Over the past decade, news organizations have often reported on the problem of climate change. Slowly, the earth’s temperature is warming. And scientists warn that this is causing extreme changes in weather and rising sea levels. We have seen many news reports about dangerous storms and severe flooding. And cities along the world’s coasts are often most affected. But now, scientists are warning of a new problem for coastal cities: land subsidence. Major cities around the world are sinking. Scientist Gilles Erkens told the BBC news organization,
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"Land subsidence is a bit of a hidden problem. Sea level rise has been in the news. And it is a major problem. But land subsidence is adding to the problem of sea level rise... We are going down, and the sea is coming up."
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The problem of sinking cities may seem frightening. But scientists believe there are achievable solutions. Today's Spotlight is on land subsidence.
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Currently, half of the world's population lives in cities. And the number of people living in cities is quickly growing. By 2050, scientists estimate that 2/3 of the world’s population will live in cities. Many of these cities are megacities - they have a population of ten million or more people. And many of these megacities are on the coast. In these cities, the danger of flooding from rising sea levels is great. And the problem of land subsidence is greatly increasing their risk of severe flooding.
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Deltares Research Institute recently released a major study on the global problem of land subsidence. Gilles Erkens presented the results at a general assembly of earth scientists. Erkens warned that some of the world's great coastal cities are at risk. In some places, the land is sinking ten times faster than the sea is rising! Important cities like Jakarta, Indonesia, Ho Chi Minh City, Vietnam and Bangkok, Thailand are in danger. In the past 30 years, North Jakarta has sunk 4 meters! Without action, these cities could soon sink below sea level.
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When cities sink below sea level, floods happen much more often. The floods are deeper. They reach further into the land. And they last longer. Severe floods are also more likely to kill people. The cities’ poorest citizens are often most at risk. In many megacities, large groups of poor people live in areas that have not been planned by the government. Millions of these people do not have protection from floods. Floods can also destroy whole systems in a city - roads, underground pipes, and buildings. Repairing this kind of damage is very costly. And it can negatively affect the economy. Erkens estimates that flood damage costs billions of dollars every year.
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So what causes cities to sink? And what can these sinking cities do to stop it? In some cases, sinking land happens from natural causes. Sometimes, a city is just built on soft soil. But Erkens reports that the main cause of land subsidence is ground water extraction. Cities often get their drinking water from under the earth. They dig deep into the ground under cities and pump large amounts of water out. This ground water extraction is common. It is an easy way to provide water for growing cities. Extracting ground water is not always a problem. But, it becomes dangerous when cities take too much, or take it too quickly.
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Today, many cities are growing fast. And sometimes they remove water too quickly. This was a problem in Tokyo, Japan. In the 1960’s, Tokyo’s ground water extraction policies caused major damage. At its worst point, the city sank by two meters in ten years! However, in the 1970’s, city officials reduced the amount of water they pumped out of the ground. Immediately, the city’s rate of sinking began to slow. Now, land subsidence in Tokyo has almost completely stopped!
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Like in Tokyo, the most immediate step toward solving the problem of land subsidence is to reduce ground water extraction. But this can be difficult and complex - especially for the governments of poorer megacities. If governments reduce ground water extraction, they need to find other ways to get water. Identifying new water resources and building new systems to use the water is costly.
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One solution is to build water treatment plants. These treatment plants can clean surface water from rivers or lakes. Other solutions deal with reducing water waste. Cities can fix leaks in their current pipe systems. They can also recycle more water. When people find more ways to re-use water, they waste less.
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Governments can also decrease land subsidence by repairing the surface of the land. They can bring more soil into wet, low-level areas. This can strengthen land. Governments can also make building companies use lighter building materials. This will reduce the amount of pressure on the soil.
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There are many different ways to reduce land subsidence. Each city needs to work hard to find the best solutions for its population. The city of Dhaka is a good example. The Deltares Research Institute reported that Dhaka is one of the cities most at risk for land subsidence. Dhaka has a population of 12 million people. It is a large city, but it is not rich. And it has limited resources to manage the problem of land subsidence.
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In 2011, the government in Dhaka began to actively fight land subsidence. It made a law that houses had to use rainwater harvesting. When homes collect and use rainwater, they use less water from the city. South Korea is also helping the government of Dhaka to build water treatment plants. These factories will help Dhaka clean and reuse water. Both of these acts will reduce the amount of water Dhaka needs to remove from the ground!
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In 2011, the Global Water Summit organization gave the government of Dhaka an award for its efforts. Dhaka still has a lot of work to do. But their changes are making a real difference in the fight against land subsidence. The government of Dhaka may not be rich and may not have the newest technology. But their example shows that recognizing the problem and deciding to act are the most important resources for saving the world’s sinking cities!
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The writer of this program was Jen Hawkins. The producer was Mark Drenth. The voices you heard were from the United States and the United Kingdom. All quotes were adapted and voiced by Spotlight. You can listen to this program again, and read it, on the internet at www.radioenglish.net. This program is called, “Sinking Cities."
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