How is streamflow affected?
Most streamflow in the West is produced by melting snow in the spring (in general, about 75 percent). At lower elevations rain can be an important component of streamflow. El Nino effects on streamflow are magnified versions of the effects on the climate elements. Because of hydrologic lags (snow does not usually begin to melt until spring), the effects of El Nino are typically delayed, in some cases for several months. Thus, the effects of El Nino on streamflow may not be manifest until late spring or summer. Usually, El Nino results in less streamflow to the Pacific Northwest and greater streamflow in the Southwest.
