Ground-Based GPS Measurements of Precipitable Water Vapor and Their Usefulness for Hydrological Applications

Half-hourly ground-based GPS measurements of precipitable water vapor (PWV) from January 2009 to December 2012 are analyzed to investigate their potential 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 rather 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 accompanied by a sudden lowering of surface pressure; (ii) Precipitable water tendency (DPWV) becomes increasingly small moving from half-hour to monthly time scale, but not negligible compared with both the moisture flux divergence div(Q) and the imbalance between actual evapotranspiration and precipitation (E–P), especially during spring and fall; (iii) GPS observations, jointly with other meteorological data, can provide an accurate estimate of the imbalance (E–P) that is of interest for drought assessment, and of the terrestrial water storage rate of change that is known to be difficult to measure; (iv) the availability of on-site precipitation observations allows the computation of precipitation efficiency, which is a key parameter for estimating the water availability in a given area and monitoring dry/wet spells. 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.