Rainfall Ensemble Member-Generation Method Accounting for Regional Characteristics

Abstract

This paper proposes a method for generating rainfall ensemble members by considering regional characteristics. The movement directions of storms (characteristic direction) and spatial distribution of rainfall intensity (rainfall-intensity weight) are considered as the regional characteristics. As a case study, grids for the ensemble simulation are set in Seoul, Korea, where the rain-gauge density is quite high. The characteristic direction and rainfall-intensity weight of each grid are determined based on observations of major storm events that occurred in Seoul during the last 10 years. The rainfall ensemble members are generated by considering the characteristic directions quantified using the beta distribution. A total of 100 rainfall ensemble members are generated by repeating the simulation of the storm movement. The result from the simple average of these ensemble members is considered as the ensemble mean. The rainfall ensemble members and ensemble mean are evaluated based on the rainfall-intensity weights. The rainfall ensemble members generated using various types of rainfall fields are found to be very similar to the spatial distribution of the rainfall-intensity weights. The ensemble mean is also found to exhibit average characteristics of the rainfall ensemble members. The same results are also derived from the simulation of the storm event that occurred in 2018. Keywords: Regional Characteristics, Rainfall Ensemble, Characteristic Direction, Rainfall Intensity Weight, Beta Distribution