This study examined the correlation between rainfall and zenith total delays (ZTDs), which are derived from the global positioning system (GPS). Furthermore, this study analyzed feasibility assessment of heavy rainfall
forecasting using GPS-derived ZTDs during typhoons. Typhoon Soudelor (in August, 2015) and Typhoon Dujuan (in
September, 2015) were selected as the study cases. We used the point precise positioning (PPP) method with Bernese
5.2 software to compute ZTDs at 17 GPS stations during the study periods. The ZTD results derived from the PPP
method were compared with those derived from the double-differencing method. We also collected rainfall data from
the rainfall stations of the Central Weather Bureau in Taiwan and analyzed correlations between the ZTDs and rainfall at these selected GPS rainfall stations. The cross-correlation method and ZTD-derived slope were used to assess the feasibility of heavy rainfall forecasting. Our results indicated that the cross-correlation method is unfeasible for heavy rainfall forecasting during typhoons. The results of the ZTD-derived slope indicated an obvious ZTD peak (extreme value) before heavy rainfall at each station during the two typhoon events. Therefore, using GPS-derived ZTD for heavy rainfall forecasting has great potential for future application.
Key words: Global positioning system, zenith total delay, heavy rainfall forecasting.