i-Tree Support Forums

We've identified a bug in which evapotranspiration (ET) does not reset at each timestep. The code is incorrectly accumulating ET from timestep to timestep. Changing this greatly affects the pervious and impervious flow. This is due to the fact that the cumulative infiltration calculation is:
Where cumInfilQ is cumulative infiltration, BQ is base flow, and rET is actual evapotranspiration.

With an incorrectly steadily increasing ET, we're underestimating cumulative infiltration which is allowing for much greater infiltration at each timestep and underestimating pervious area saturation excess and infiltration excess runoff.

This is a known issue which will be resolved in the next update to i-Tree Hydro version 5.