  The High Altitude Water Cherenkov (HAWC) Observatory is an air shower array
located near the volcano Sierra Negra in Mexico. The observatory has a scaler
system sensitive to low energy cosmic rays (the geomagnetic cutoff for the site
is 8 GV) suitable for conducting studies of solar or heliospheric transients
such as Ground Level Enhancements (GLEs) and Forbush decreases. In this work we
present the simulation of the HAWC response to these phenomena. We computed
HAWC effective areas for different array configurations (different selection of
photomultiplier tubes per detector) relevant for Forbush decreases and GLEs.
