The increase of the amount of water taken from river course is the direct cause why observed runoff decreases . as land cover forms the boundary between the atmosphere and the terrestrial sphere , changes in land cover may have significant implications on water resources 针对减少的径流量,本文还提出了将它分为气候影响、人类活动可还原水量和不可还原水量两种,并且阐述了在现阶段,这种分类方法是切实可行的。