Found this thread while trying to find the same information about what exactly is in SFCEVP.
I did some looking around in the code of the LSM I'm using (Noah) in version 3.8. It looks like SFCEVP is set from QFX in module_surface_driver.F. Within Noah's source code (specifically the code within module_sf_noahlsm.F), you can find the variable QFX_PHY. QFX_PHY is set by summing together other evaporation & transpiration variables. Like this...
QFX_PHY = EDIR1+EC1+QFX_PHY
Here EDIR is direct soil moisture evaporation and EC is canopy water evaporation.
In a different spot in the code, the plant transpiration from root layers (ET) is also added in.
QFX_PHY = QFX_PHY + ET1(K)
Based on what I've found, I'd say that SFCEVP is meant to comprehensively represent evaporation and transpiration from all sources at the surface.