If you’re a developing nation, don’t worry about having a sparse network of rain gauges: All you need is good cellphone coverage. Because raindrops both scatter and absorb radiation traveling through a storm, several teams have proposed monitoring variations in the strength of signals bounced between cell towers as a way to measure rainfall. The method has even been shown to work in Europe and Israel, where such networks are well established and towers are relatively close to one another. Now, a field test shows the technique works in western Africa, where towers are typically farther apart than they are elsewhere. In that test, which took place during the summer of 2012, researchers measured the attenuation of 7-gigahertz microwave signals traveling a 29-kilometer path between two cellphone towers northeast of Ouagadougou once every second. Signals were measurably degraded on 95% of the days when more than 5 millimeters of rain fell at a weather station located between the two towers, the researchers report online in Geophysical Research Letters. Also, the amount of signal degradation was highly correlated with rainfall measurements at the weather station, the team notes. These results suggest the monitoring signals throughout a network of cellphone towers could help meteorologists, even those where rain gauges are few and far between, compile regional rainfall maps and provide early warning of flooding.