ANALYZING THE UNCERTAINTY OF USING SURFACE HUMIDITY FOR PMP ESTIMATION

Abstract

 The purpose of this study was to identify the uncertainty of the probable maximum precipitation (PMP) estimation method using surface dew point data under the pseudo-adiabatic assumption. This PMP estimation method was proposed by the World Meteorological Organization (WMO) and widely utilized for many practical purposes, and precipitable water (PW) is the most important parameter to estimate PMP. We evaluated the pseudo-adiabatic assumption by utilizing the reanalysis data, JRA-55, to estimate the uncertainty in the PW estimation using the pseudo-adiabatic assumption. The JRA-55 data was verified with radiosonde data at 10 points across Japan, and it shows good reliability for the dew point and PW data. Our PW verification results show that the use of the pseudo-adiabatic assumption is suitable for those areas with frequent heavy rainfall events and where the dew point is relatively high. However, the PW estimated from the assumption shows noticeable differences from the PW measured from JRA-55 data in those areas where heavy rainfalls are not frequent, and thus the estimated PMP could have large uncertainty in those areas.