水文概念之：runoff 和streamflow

runoff是坡面产流、河道汇流两个部分，而streamflow是指的河道汇流部分。

通俗理解：streamflow一般是汇流之后的，径流，单位一般是m3/s。runoff一般理解为净流深，单位是mm，可以没有汇流。GLDAS给的径流结果一般用runoff，不用streamflow，因为没有汇流模块。 streamflow是出口断面的径流量，runoff是流域整个汇流面积平均的径流深。一般没有严格的限制，很多人混用。一般都这样，不过写文章也限制的不严格，混用的也多。

Streamflow, or channel runoff, is the flow of water in streams, rivers, and other channels, and is a major element of the water cycle. It is one component of the runoff of water from the land to waterbodies, the other component being surface runoff. Water flowing in channels comes from surface runoff from adjacent hillslopes, from groundwater flow out of the ground, and from water discharged from pipes. The discharge of water flowing in a channel is measured using stream gauges or can be estimated by the Manning equation. The record of flow over time is called a hydrograph. Flooding occurs when the volume of water exceeds the capacity of the channel.