托福阅读中会出现各种不同的背景知识，所以大家要在平时备考中注意积累，觉得用得到的要记下来，本期为大家带来的是关于干旱的托福阅读材料，希望对大家的考试有帮助。
For those of us lucky enough to always have enough food and water, it may be hard to imagine living through a drought. A drought occurs when for a variety of reasons, usually including a lack of rainfall and warm temperatures. Soil moisture severely dwindles. Why and how do these meteorological events occur?
As air swirls around the earth, it rises and sinks over different areas of the globe. When air rises it cools and loses moisture. When air sinks, it grows warmer and absorbs moisture, drying out the land. Sinking air helps to form deserts, such as the Sahara Desert in Africa.
Warm, sinking air can hamper cloud formation, which results in less rain and lower overall humidity. When these conditions occur in an area that normally receives enough rain to allow plants to grow and keep water sources replenished, a drought can ensue. The Dust Bowl that affected the prairie regions of the United States was one infamous drought. An equally severe drought occurred in the United States in the summer of 1988. Rainfall over the mid-west, Northern Plains, and the Rockies was fifty to eighty-five percent below normal.
Sometimes over-farming and soil erosion contribute to drought, but there are also natural disasters that can occur even when soil is carefully preserved. And when a drought hits, there’s little that can be done to end it. Water and soil conservation can help, but until the rains come again there’s not much science can do.
以上就是本期托福阅读材料之干旱的问题，希望同学们能够有所了解。若您想了解托福考试更多相关信息请关注百利天下出国考试。
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