Articles | Volume 15, issue 12
https://doi.org/10.5194/nhess-15-2605-2015
https://doi.org/10.5194/nhess-15-2605-2015
Research article
 | 
09 Dec 2015
Research article |  | 09 Dec 2015

On the inclusion of GPS precipitable water vapour in the nowcasting of rainfall

P. Benevides, J. Catalao, and P. M. A. Miranda

Abstract. The temporal behaviour of precipitable water vapour (PWV) retrieved from GPS delay data is analysed in a number of case studies of intense precipitation in the Lisbon area, in the period 2010–2012 and in a continuous annual cycle of 2012 observations. Such behaviour is found to correlate positively with the probability of precipitation, especially in cases of severe rainfall. The evolution of the GPS PWV in a few stations is analysed by a least-squares fitting of a broken line tendency, made by a temporal sequence of ascents and descents over the data. It is found that most severe rainfall events occur in descending trends after a long ascending period and that the most intense events occur after steep ascents in PWV. A simple algorithm, forecasting rain in the 6 h after a steep ascent of the GPS PWV in a single station, is found to produce reasonable forecasts of the occurrence of precipitation in the nearby region, without significant misses in what concerns larger rain events, but with a substantial amount of false alarms. It is suggested that this method could be improved by the analysis of 2-D or 3-D time-varying GPS PWV fields or by its joint use with other meteorological data relevant to nowcast precipitation.

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Short summary
Precipitable water vapour (PWV) retrieved from GPS delay data is analysed in several case studies of intense precipitation in Lisbon. It is found positive correlation between PWV behaviour and the probability of precipitation. A least-squares fitting of a broken line tendency shows that most severe rainfall occurs in descending trends after a long PWV ascending period. A simple forecast algorithm identifies the majority of large rain events, yet with a substantial amount of false positives.
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