Simulated streamflow response to possible differences in transpiration among species of hardwood trees

Abstract

Possible differences in transpiration among species of hardwood trees were simulated in a hydrologic model, called Brook, to estimate the effects of these differences on monthly and annual streamflow. Brook is a deterministic, lumped‐parameter model that simulates streamflow from small, forested watersheds in the eastern United States. The model uses only daily mean temperature and daily precipitation as input. A 4‐week difference in timing of leaf development in spring or color change in autumn caused differences of 10–60 mm in simulated annual streamflow. When daily transpiration varied by 20%, as it might with differences in leaf diffusive resistance among species, differences in simulated streamflow ranged from 15 to 120 mm annually. Differences in root distribution with depth can affect the availability of soil water; varying this availability caused differences in simulated streamflow of 15–60 mm. In all cases the smaller differences occurred when the soil was dry at the times of differing transpiration. On a deep residual soil the differences in streamflow were spread through the year, but on a shallow till soil the differences were restricted to the months in which there were changes in transpiration. Differences in response among 15° north‐facing and 15° south‐facing slopes and a horizontal surface were south‐facing slopes and a horizontal surface were minor.