Exploiting cell-phone signal disturbances for urban flood warning systems in mega-cities

Overview:
The world population is increasing and many cities (particularly in developing countries) are expanding rapidly – often with little or no planning and associated infrastructure. At the same time, climate change predictions suggest that many parts of the world will experience increased frequency of extreme rainfalls. This make cities more vulnerable to pluvial flooding when rainfall and runoff rates exceed urban drainage capacities. This can lead to damage to buildings, traffic disruption and fatalities. Models are now routinely used for pluvial flood prediction and risk assessment, with ever-increasing spatial and temporal resolution. However, these models need accurate and timely measurements of surface precipitation: radars (e.g. the Met-Office radar network) and telemetry-linked rain gauges have been traditionally adopted for rainfall estimations. However, radar is known to suffer from several issues including occultation by clutter and degradation of resolution and decrease in accuracy with range. Furthermore it is not available in the majority of developing countries. In many parts of the world the density of surface precipitation gauging networks is rapidly declining and only few gauges are telemetrically linked. One alternative is to use the received signal level data from the enormous number of microwave links used in commercial cellular communication networks and/or from satellite TV antennas. Commercial link networks cover large parts of the land surface of the earth and have a high density, particularly in urban areas. Satellite TV dishes have even greater potential in terms of crowd-sourcing precipitation data. Rain induces attenuation in the radio signals that propagate from a transmitting to a receiving antenna (for cell-phone links) or from the satellite to the TV dish. The signal attenuation between transmitter and receiver is almost linearly related to the path-averaged rainfall intensity. This attenuation can be calculated from the difference between the received powers with and without rain. This concept is now well-established for cell-phone links [e.g. 1,2] and is currently under investigation for satellite TV downlinks. However, its exploitation as an input in urban hydrological models [3] and the development of flash-flood early warning systems in (mega)cities has yet to be attempted.