Crowd-sourcing high-resolution precipitation dataset in smart cities for urban flood risk modelling

With the constant increase of population and the associated land cover changes, cities become more vulnerable to persistent rainstorm waterlogging due to excess surface runoff and sewer surcharge, which in the most serious cases can trigger flash floods and fatalities or, more frequently, can cause damage to buildings and disruption to traffic.

Models are now routinely used for flood prediction and risk assessment, with ever-increasing spatial and temporal resolution, but they need accurate and timely surface precipitation measurements at unprecedented temporal and spatial resolutions.

Radar networks (e.g. the UK Met-Office radar network) and rain gauges have been traditionally adopted for rainfall estimations. However, radar estimates are known to suffer from several issues (occultation by clutter, degradation of resolution and decrease in accuracy with range from the radar, etc) which will only be partially mitigated by the upgrade of most of the national radar networks to polarimetric capabilities. Moreover, in many parts of the world the density of surface precipitation gauging networks which are used to calibrate the radar estimates is rapidly declining. This can potentially be counteracted by using 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 a greater potential in terms of crowd-sourcing precipitation data. Rain induces attenuation in the radio signals that propagate from a transmitting antenna at one base station to a receiving antenna at another base station (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 has already been proved valid for cell-phone links by several scientists [e.g. 1,2] but it is still in fieri for satellite TV downlink. Once these line-path-averaged products became available it is paramount to properly merge them with traditional precipitation products and to evaluate their impact in hydrological models.

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