Heavy rain floods canals and streets. Gaining more knowledge about rainfall would allow to more effectively manage canalization systems.
The Swiss Eawag analyzes the signal quality between radio towers of mobile network operators for that purpose. Due to the fine-grain deployment of mobile networks they claim to achieve more accurate measurements than the coarsely deployed weather stations can do. Comparing the data of 23 cell towers with 13 rain weather stations over a period of two months they could calibrate their system and derive rainfall from signal disturbance. Find details in German here.