Learning from Forests

Forests play a significant role in the process of moving water throughout the landscape. As we learned from Eli Asarian’s recently published report on streamflow and precipitation trends in the Eel River basin, the age and density of our forests impacts streamflow in a measurable way.


Because evapotranspiration is such a large portion of the annual water budget, small changes in evapotranspiration have the potential for large effects on summer streamflows. The Eel River Basin’s forests have undergone substantial changes in the past century as a result of timber harvest and fire suppression. Without fire or mechanical intervention, Douglas-fir trees are invading prairies and oak woodlands, potentially increasing evapotranspiration. The young dense forests of the Eel River Basin may be in a state of maximum evapotranspiration. Bull Creek provides evidence supporting the hypothesis that vegetation change is contributing to streamflow declines, because despite lacking water diversions it had the largest number of days (and nearly the greatest magnitude of declines) with declining precipitation-adjusted streamflow (Figure ES-1), coinciding with the regeneration of its forests following intensive logging that occurred prior to installation of the stream gage in 1960.

Asarian, 2015

While our local forests – young, dense, and unnaturally uniform – are reducing streamflows, the shrinking Amazon rainforest may be losing its ability to generate its own rain. In a recent NPR interview, climate scientist Antonio Nobre describes how the Amazon functions not only as the lungs of the earth, but also like a beating heart. Acting as a bionic pump, the Amazon draws water from the earth and transpires the water into the air, essentially providing its own irrigation at roughly 20 billion tons of water per day.

Listen to the NPR interview here: