The event occurred, he believes, when a series of phenomena called atmospheric rivers stalled over California.

他认为这样的事件发生时一系列现象恰好也发生了，即大气流在加利福尼亚停止了。

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"Most flooding events in the major rivers on the West Coast are a result of atmospheric rivers creating copious rainfall," Ralph said.

在西海岸大部分主要河流发生的洪水事件都是由于大气流的因素引发的大量降雨所致，拉尔夫教授称。

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There is also the awkward fact that although there is eight times more atmospheric water than in all the rivers of the world combined, it is unevenly distributed.

还有一个比较尴尬的事实：虽然空气中的蓄水量是全球所有河流蓄水量的八倍之多，但是空气中的水分布不均。

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The University of Reading says it is coming in the form of atmospheric rivers - narrow bands of atmospheric moisture, thousands of kilometres long, transported by the wind.

BBC: Floods: how much can new barriers help?