On the potential of ground-based GPS measurements for monitoring dry/wet events

Half-hourly ground-based GPS measurements of precipitable water vapor (PWV) from January 2009 to December 2012 are analyzed to investigate the potential of such data for hydrological applications at basin level. In particular, the usefulness of these high temporal resolution data for monitoring extreme weather conditions such as floods and meteorological dry/wet spells is discussed. Two sample GPS stations in U.S. from the SoumiNet network are considered that have continuous data for the last four years and a few missing values. Results suggest that: (i) A flood event is characterized by an anomalous increase of PWV and surface pressure lowering; (ii) Precipitable water tendency (DPWV) becomes increasingly small moving from half-hour to monthly time scales, but not negligible compared with both the moisture flux divergence div(Q) and the unbalance between evapotraspiration and precipitation (E–P), especially during spring and fall; (iii) GPS observations, jointly with other meteorological data, can provide an accurate estimate of the unbalance (E–P) that is of interest for drought assessment, and the rate of change of the terrestrial water storage that is known to be difficult to measure; (iii) the availability of on-site precipitation observations allow the computation of the precipitation efficiency, which is a key variable for estimating the water availability in a given area and monitoring drought. It appears that for a comprehensive monitoring of a river basin, a GPS network that encloses the area of concern, equipped with meteorological ground sensors, is suitable and desirable