The amount of delay in rainwater storage and runoff in green roof depends on the type of soil, thickness, water content, type of plant, growth condition, and roof slope, etc., but the effect of soil is large. In this study, we focused on the soil, and examined a simple method to estimate the delay of rainwater storage and runoff. The method is to determine the macropore volume involved in drainage from the transition of the water content of the soil during rainfall and the moisture characteristic curve, and to determine that the macropore volume equals the amount of rainwater storage.
