RHESSYs (The Regional Hydro-Ecologic Simulation System) is a state-of-the-art hydrologic model that simulates climate, plant, soil, and river processes across an entire watershed. It is especially useful for this project since in eastern Washington and northern Idaho, the amount of rain or the temperature can be very different in a watershed depending on where you are in the watershed. It is also very useful since it can simulate key factors that determine tree mortality in a drought. Specifically in can simulate subsurface moisture and tree and soil carbon and nitrogen.

 

A more thorough description of the model can be found here. If you want to dig into the nuts and bolts of the model, the code for the model can be found here. RHESSys model results were also mentioned (by Dr. Tague) in a recent Economists article!