干旱的成因-都是空氣惹得禍

導讀：截至今日，云南、貴州、廣西、重慶、四川5省區(qū)市耕地受旱面積1.01億畝、占全國的84%，作物受旱7907萬畝，待播耕地缺水缺墑2197萬畝；有2088萬人、1368萬頭大牲畜因旱飲水困難。如此嚴重的旱災不得不令人反思，我們做錯了什么，今后將怎么做。

 

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 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?

對于那些幸運的、總有足夠的食物和水的人來說，很難想象在干旱之中的生活。引發(fā)干旱有多種原因，通常包括缺少降水和高溫。土壤中的水分嚴重減少。這個氣象現(xiàn)象的成因和原理又是什么呢？

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.

空氣在地球上方旋轉流動，沉浮于不同的地區(qū)。當空氣上升時，溫度降低，失去水分。當空氣下降時，溫度上升，吸收水分，致使地面干燥。下沉的空氣是撒哈拉（在非洲）等沙漠形成的幫兇。

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.

溫暖、下沉的空氣能夠阻礙云的形成，致使降雨減少，空氣和土壤的濕度降低。這種狀況如果是發(fā)生在平時雨水充足，能讓植物生長，并通過植物保存水分的地方，旱災就會隨之而來。沙塵天氣波及到了美國的大草原地區(qū)，造成了十分嚴重的旱災。在1988年的夏天，美國也曾發(fā)生過同樣嚴重的旱災。在中西部，北部平原和洛磯山脈，當時的降水量是平常的百分之五十到八十。

Sometimes over-farming and soil erosion contribute to drought, but there are also natural disasters that can occur even when soil is carefully preserved. 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.

有時，過度耕種和土壤侵蝕都能造成干旱。但是，盡管有時人們很注意保護土壤，旱災依然會發(fā)生。當干旱來臨時，我們對它便束手無策了。注意水土保持能管用，但是，在雨水重歸大地之前，科學家們也幫不上什么忙。