在自然条件下，降雨集中、强度大、历时短、暴雨中心靠近流域出口，洪峰流量就会比较大，反之则小，但在人类活动影响下则不一定产生这样的结果。

Runoff yield and flood peak are larger when the rain center is near the outlet of watershed under the natural environment, but it is not necessarily under the human activities environment.

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如果列不包含空值，则SQL使用一个包含一个0的小整数；反之则包含- 1。

SQL USES a small integer which contains a zero if the column is not null or -1 if the column contains nulls.

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