Solarpunk stories are often stateless or

This at least avoids the absurdities of modern borders, which often divide communities

In a world where states no longer exist, borders drawn by nature may be very useful for administrative purposes. People will still need to coordinate over land and water management.

They give some wonderful world building suggestions though I’d also suggest that as Fully Automated! Is in the transition to a post-state world, but is not there yet, that there’s excellent potential for factions, feuds, drama, and plot hooks in the existing states losing relevance to watershed organizations that overlap their territory and authorities, but don’t necessarily encompass all of them.

The cool thing with watersheds is you can aim for huge nation-sized chunks of land, or tiny town-sized boundaries, all depending on your needs.

Depending on what's being managed, dividing things by biome or hardiness zone might make more sense