The research shows that during the 20th Century rainfall in the Sahel dropped between 20 and 30 percent.
研究显示在20世纪期间,撒海尔的降雨下降了20%到30%。
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Possible causes of the vegetation shift include declining rainfall, growing human population and decreasing soil fertility
可能造成植被转移的原因包括降雨量的下降、人口的增长以及土壤肥力的减弱。
One in six trees died in the last half of the 20th century and second one in five tree species disappeared locally and then third, together, these changes shifted vegetation ___ southwards towards areas of more rainfall.
One ? is died in the last half beteen 20 century, and second one in five tree speech is disappear locally. and then third, together these changed shifted vegetation though ? world area of marine ?