Characterisation of Mediterranean heavy rainfall events from GPS water vapour monitoring

Laboratoire de Géophysique Interne et Tectonophysique, Université Joseph Fourier / CNRS, Grenoble, France
04/2010; 12:11626.

ABSTRACT High precipitating events occur regularly during autumn season in South
of France along the Mediterranean coast. These extreme precipitation and
flooding events produce societal damages. The main limitation to improve
the forecast of such events relies on the knowledge of the initial water
vapour field (Ducrocq et al. 2002). Usual water vapour observation
instrument (radio-sounding, radiometers...) fail to characterize
mesoscale distribution of moisture. For a decade, GPS receivers have
shown their ability to provide humidity estimation. Thus, GPS dense
networks are unique to provide vertically integrated tropospheric water
vapour observations. In this work, we use a four years GPS data set
from a GPS network to better characterize humidity field in Southern
France (mainly Languedoc-Roussillon and Provence) before and during
heavy rainfall events. After looking through about 40 study cases a
selection of 14 events has been applied. GPS data analysis, rain gauge
measurements and satellite wind data are used in accordance with rain
location and GPS water vapour mass monitoring. Our systematic GPS data
analyses during several HPE events revealed that multiple HPE schemes
arise from combining humidity monitored by GPS with wind surface
information, in particular, thanks to the unique spatial and temporal
resolution of the GPS data. For most events, a high correlation is found
between the topography of the coast, the direction and location of the
moisture fluxes and the location of the rainfall. For all the cases,
the study of ZTD temporal variations revealed some difficulties to be
explained using simple physical processes. Some characteristics HPEs
events will be presented.