Thank you so much for your response. you mean the software considers rain or snow during simulation, true? Also, do you know how can we set irrigation schedule for a green roof? Also, is it possible to model drainage layer for a green roof in openstudio or Energyplus?

Sorry if I ask so much. Thanks for your kind consideration.

Reading the docs for the EnergyPlus object, it is meant to be used on flat or low sloped roofs. so when it rans, the soil should be able to store water until it is at capacity, at which point it would overflow to the ground. I'm not that familiar with this object, but now there are fields about the plants resistance to moisture transport, as well as the soil moisture characteristics. Maybe someone else can point to a research paper or more detailed documentation.

Irrigation is tricky, I assume you just want to do this until plants get established so they don't die. You could simulate a typical (post irrigation) year, unless you plan for ongoing irrigation all of the time. Otherwise you could alter the weather file (seems like a lot of work) or find a way to alter the soil characteristics on roof to prevent it from every fully drying out, or have thermal characteristics of moist soil). My advise would be to ignore irrigation.