Prof Dr Nick van de Giesen, Dr Eugenio Realini
African weather is poorly monitored, especially for forecast purposes. At the same time, African societies are vulnerable to extreme weather events. By far the most critical weather variable is rainfall. To make good predictions about rainfall, it is important to know how much water vapour the atmosphere contains. More water in the atmosphere means more rainfall. Traditionally, this amount of water is measured by weather balloons, but these are expensive and there are only few regular launches over Africa. GNSS signals travel slightly more slowly through moist air than through dry air. A GNSS receiver can measure the extra delay caused by moisture in the atmosphere, even though the differences are very small. Today, even low-cost GNSS receivers are so accurate that they can measure these delays. The plan is to add these low-cost GNSS receivers to the stations of the TAHMO (Trans-African Hydro-Meteorological Observatory, www.tahmo.org) network around Lake Victoria. TAHMO is building a network of 20,000 robust and cost-efficient weather stations across Africa. By adding GNSS/Galileo receivers, it will be possible to greatly improve rainfall predictions.