Gieß Den Kiez – CityLAB Berlin

Because the page is in German only (but fairly self-explanatory imho): this maps the 625k registered trees in Berlin and crosses the data set with rainfall patterns showing which trees need attention of neighbours to survice. You can "claim" a tree and mark it as taken care of.

I believe the origins of this are two heavy draught periods summer 2018/2019 where many trees succumbed.