English to German Science Environment & Ecology Hydrologie

Context:
"Streamflow. Changes in temperature, precipitation, snowpack, and glaciers can affect the rate of streamflow and the timing of peak flow. Over the last 75 years, minimum, maximum, and average flows have changed in many parts of the country—some higher, some lower. Most of the rivers and streams measured show peak winter-spring *****runoff***** happening at least five days earlier than it did in the mid-20th century."

Die englische Definition lautet:
"Water from rainfall, snowmelt, or otherwise discharged that flows across the ground
surface instead of infiltrating the ground."

Vielleicht Abfluss? Aber was ist dann Streamflow?
Danke schön im Voraus!