INVESTIGATION ON THE SCALE OF RAINFALL SPATIAL VARIABILITY TO BE CONSIDERED IN RUNOFF SIMULATION

A rainfall spatial variation scale to be considered in a runoff simulation will be investigated using meshtype rainfall data and a distributed runoff model. At first, a runoff simulation is conducted by using a mesh-type rainfall data as it is, and the result is regarded as a standard result. As the next step, the rainfall data is averaged in some area and a runoff simulation is conducted by using this averaged rainfall data. If we have little difference between the standard result and the result obtained by using the averaged data, we do not have to explicitly consider the rainfall spatial variability in the area where the data is averaged, and we have only to use the average rainfall data as an input data of the simulation. Conversely, if the difference is large, we have to consider the rainfall variability in the averaging area when conducting a runoff simulation. These numerical experiments indicate that it is important to find out the rainfall spatial variability which affects the results of runoff simulations and the scale changes with basin size.