Monitoring water vapour with GNSS during a heavy rainfall event in the Spanish Mediterranean area

The Spanish Mediterranean area is periodically affected by torrential rainfall events during autumn. In September 2012, one of these episodes took place with up to 50 mm of rain in a 1-hour period and with more than 300 mm in 12 hours. This study shows the spatial and temporal variability of the atmospheric integrated water vapour (IWV) observed using delays in Global Navigation Satellite System (GNSS) signals and associated rainfall during this severe weather event. This experiment focuses on the relationship between the variations of IWV values in GNSS stations and meteorological variables such as atmospheric pressure and precipitation. This study was carried out on the Mediterranean coast of Spain during a heavy rainfall episode. The results show a mean increase in IWV of around 30 kg/m(2) occurring prior to heavy precipitation. They further revealed an increase of up to a 100% in IWV values in several GNSS stations available in the study area. Fluctuations in IWV fields correlate well with approaching frontal rainfall and a combined rise in IWV and a drop in atmospheric pressure may well be used as a pre-cursor to heavy precipitation.