In cities I can imagine an apparatus not unlike a retractable roof in function, spanning the gaps between buildings. It would capture rainfall and prevent flooding while keeping citygoers dry. The "rooves" themselves would channel water as would an aqueduct, possibly reorienting themselves to better handle local downpours. The underside would need to emit light, whether transmitted natural light or otherwise.
Such a system would bring ancillary benefits of improving travel safety in the city, and reducing the need for road maintenance and vermin control (esp. mosquitoes).
I imagine the biggest technical challenge to be durabiity: The need to be resilient against hail, high winds and flying debris. And should it fail at the worst time ... an awful thought! But levees are a similar technology in that regard.