Abstract
GPS (Global Positioning System) is a sophisticated system that performs a precise positioning with higher accuracy in space using GPS satellites. In the last decade, techniques have been developed to infer the total amount of water vapor in the atmospheric column having infinite height as GPS-derived precipitable water vapor (GPS-PWV). In this study, using GPS-PWV data, monthly potential evapotranspiration was estimated at a plain in the northern part of Kyushu Island, Japan, based on the close correlation between screen-level vapor pressure and GPS-PWV shown by a preceding study. It was confirmed that the vapor pressure estimated from GPS-PWV concurs with the observation. The standard deviation of the difference between the estimated and observed vapor pressures was 1.7hPa. The formula, which does not use vapor pressure but GPS-PWV, was presented to estimate the monthly potential evapotranspiration at the study area. The estimated values of the evapotranspiration ETGPS agree well with the calculated values ETPEN from Penman's formula. Finally, it was suggested that values of ETGPS derived considering the influence of Δe possibly over- or underestimating evapotranspirations, by as much as 20 % in spring, summer and autumn or 50 % in winter of ETPEN.
