pan evap coefficient
I had a very interesting discussion with @westerma yesterday. He looked through the mHM code quite carefully trying to understand how mHM is working. I was able to clarify most of his questions, but not the following:
For ET from sealed areas, there is a correction factor (evap_coeff in line 195 in mo_soil_moisture.f90).
aet_sealed = (pet / evap_coeff - aet_canopy) * (storage_sealed / water_thresh_sealed)
The coefficient is specified in the mhm.nml and reduces PET during winter and increases it during spring. My question to @lese and @rkumar: What is the idea behind this correction? Is there a reference for this correction?
I guess we should implement it in a spatially varying fashion similar to the night factors for precip and temperature. I would assume that applying this correction in a global setup makes little sense, although the overall effect is not big as it only affects sealed areas.