Evaluation of reanalysis precipitable water vapor under typhoon conditions using multi-source observations

Abstract. Precipitable water vapor (PWV) exhibits rapid and complex variations during typhoons, and its evaluation under typhoon conditions remains challenging due to sparse observations over the oceans. This study systematically evaluates PWV estimates from three state-of-the-art reanalyses during 113 typhoons between 2020 and 2024 over the Northwest Pacific and East Asia. The fifth-generation European Centre for Medium-Range Weather Forecasts Reanalysis (ERA5), the Modern-Era Retrospective Analysis for Research and Applications Version 2 (MERRA-2), and the Japanese Reanalysis for Three Quarters of a Century (JRA-3Q) are compared with ground-based Global Navigation Satellite System (GNSS), radiosondes, and radio occultation (RO) observations. Results based on ground-based GNSS show that ERA5 provides the highest accuracy, with a bias of −1.65 mm in non-typhoon periods and an even smaller bias of −0.29 mm during typhoons, and root mean square error (RMSE) decreasing from 3.52 mm in non-typhoon periods to 3.40 mm during typhoons. JRA-3Q also has smaller error during typhoons compared to non-typhoon periods though its bias and RMSE remain relatively large. Conversely, MERRA-2 shows higher error during typhoons compared to non-typhoon periods, shifting from a modest underestimation of −0.53 mm in non-typhoon periods to an overestimation of 0.86 mm during typhoons, but still maintains accuracy throughout typhoon periods. PWV estimates from all three reanalyses show high correlations with those from radiosonde and RO observations. These results provide a comprehensive accuracy reference and confirm the suitability of reanalyses for PWV researches during typhoons, with ERA5 appearing the most reliable among the datasets evaluated.