Heavy rain analysis based on GNSS water vapour content in the Spanish Mediterranean area

Abstract

For improved water resource management and forecasting of risks associated with hydrological processes, it is fundamental to improve the knowledge of rainfall as a natural process. Atmospheric water vapour content is one of the key variables in precipitation. The distribution and evolution of atmospheric water vapour is critical for the functioning of hydrological processes, being one of the essential climate variables as defined in the Global Climate Observing System. Improving understanding of atmospheric water vapour content and distribution is essential for climate change studies because water vapour is the main greenhouse gas, contributing around 70% of global temperature rise (Solomon et al., 2007). Water vapour is also a major component in controlling atmospheric stability, because it is involved actively in the evolution and propagation of convective storm systems. Until recently, atmospheric water vapour could not be observed particularly well due to the absence of instruments capable of measuring it at high-resolution temporal and spatial scales. However, in recent years the increase in the number of permanent GNSS (Global Navigation Satellite System) reference stations worldwide has led to a major breakthrough in the monitoring of atmospheric integrated water vapour (IWV), with almost 2000 sites in Europe alone contributing near real-time atmospheric delay estimates. The present study focuses on the relationship between variations in IWV observed using delays in GNSS signals with meteorological variables such as atmospheric pressure and precipitation, in a long-term study for the period 2000–2012 in the area of Valencia, Spain. Fluctuations in IWV fields correlate well with approaching frontal rainfall, and a combined rise in IWV and fall in atmospheric pressure act together as a precursor to heavy precipitation.