It is possible to easily perform the spatial simulation for a large area. Provided is a computer-readable medium recorded with a spatial simulation program for controlling a computer to execute procedures for calculating a time-based change of a variable in a plurality of numerical grids to reproduce on a computer a time-based change of a phenomenon represented by the variable in a space represented by the plurality of numerical grids, the spatial simulation program including the procedures of: defining a sub domain composed of the plurality of numerical grids (201); setting a forcing condition for the sub domain (204); detecting the sub domain including the numerical grid in which the variable changes with time; detecting the sub domain including the numerical grid in which the variable referred to for calculating the time-based change is positioned (205); and updating variables in the numerical grids constituting the detected sub domain (208).