At school you read about science, history and geography in English, and you answer exam questions about them. Read this short article, then answer 2 exam-style questions and write one answer yourself. Everything you need is in the article.
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On some afternoons in Kuala Lumpur, the sky turns dark and a storm drops more rain in one hour than London gets in a month. Within minutes, some roads look like rivers. Yet the same storm over a forest in Pahang causes no flood at all. Why does the city flood while the forest does not?
Start with what happens to rain in a forest. The , the leaves and branches of all the plants, catches much of the rain, so it reaches the ground slowly. The soil is soft and full of tiny spaces, so the water can : it soaks down into the ground. From there it moves slowly through the soil and rock, and reaches the river hours or even days later. The forest works like a sponge. Only when the soil is , so full of water that it cannot hold any more, does the water start to run across the top.
Now look at a city. Roads, car parks and roofs are : water cannot pass through them. Instead of soaking in, almost all the rain flows across the surface. This moves fast, because concrete is smooth and there are no plants to slow it down. Engineers build drains to carry it away, but every drain is designed for a certain amount of water. In a very heavy storm, the drains cannot cope, and the water rises in the streets.
There is a second problem. In a forest, the rain reaches the river slowly, over a long time. In a city, it arrives almost all at once. The level of the river rises very quickly to a high peak, and if the peak is higher than the river banks, the river floods. As cities grow, more and more land is covered in concrete, so the problem gets worse. This growth of towns and cities is called .
Cities can reduce the risk. Some plant trees and build parks, where water can soak into the ground. Others build large ponds that store water during a storm and release it slowly afterwards. Kuala Lumpur built the SMART Tunnel, which diverts flood water away from the city centre: when the river is too high, the water goes into the tunnel instead of into the streets. None of these ideas stops the rain. They all work by slowing the water down, so it reaches the river over a longer time.
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Compare what happens to heavy rain that falls on a forest with heavy rain that falls on a city.
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Create a free accountArticle written for Axiom. Word levels: CEFR-J Wordlist v1.6 (Yukio Tono, TUFS) · Octanove Vocabulary Profile C1/C2 (CC BY-SA 4.0).