Rainwater harvesting is a viable approach, both when water is scarce and when too much of it falls from the sky.
It can be collected with comparatively simple means and stored for dry periods. This way, it can be used later for irrigation, washing and, in particularly affected regions of the world, also for drinking, while other water resources are conserved.
If the rain is directed into a storage tank during the next thunderstorm, it will not flood the streets. The rain storage tank can absorb the water like a sponge, stockpile it and release it when needed. Many small, decentralized rainwater storage tanks can add up to a very large retention volume for flood protection.
Using rainwater is a simple way to create real value: Clean Water.
The value of water and how it is assessed is also the subject of the United Nations' World Water Report 2021, published to coincide with World Water Day. The report describes the value of water from different perspectives and how this can be measured.
Find an english summary about the report here:
World Water Report 2021
The use of rainwater is an active contribution to sustainable development. The member states of the United Nations have set themselves 17 goals, of which rainwater harvesting supports several. Foremost among them is the sixth:
Ensure availability and sustainable management of water and sanitation for all.