Correlation and causal relationship between GPS water vapor measurements and rainfall intensities in a tropical region (Tahiti-French Polynesia)

We processed a eight-year time series (2001-2008) of zenith wet delay and associated precipitable water (PW) contents from the permanent GPS station THTI (OGT) and a corresponding precipitation time series from the pluviometer of the Matatia valley (7 km South East from the GPS receiver). Daily GPS data were obtained (including zenith total delay and North and East gradients) by applying the PPP strategy of the GIPSY-OASIS II package w.r.t. IGS final products. We used the Saastamoinen model to extract the hydrostatic part of the delay. Taking into account surface meteorological measurements, we transformed the resulting wet delay into an estimate of PW above the receiver. The precipitation dataset consisted of rainfall gauge measurements spanning the same period provided by the "Direction de l'Equipement" (GEGDP). This work poses a preliminary diagnostic on the evolution of PW and precipitations over French Polynesia with emphasis on a broad range of timescales, from seasonal to diurnal components. Before this study, no monitoring system had provided accurate and quasi continuous measures of PW in French Polynesia.