I think these look great! It’s definitely possible to have elevated cities and this was a common solution for cities in flood-prone areas prior to modern flood-control infrastructure like dams and levees.
I would look to real world places for inspiration. Many seaside towns reserve the first floor for parking because of possible storm surges. Obviously parking isn’t really needed in a solarpunk city, I would think about uses for this space that can either survive or be easily moved in the case of flooding. Your ideas seem fine although the marketplace would have to be thoughtfully designed to make it portable.
My city of Sacramento historically was very flood prone (and arguably still is, if the levies fail). An interesting feature of our history is that the entire existing downtown was lifted up to reduce flooding risk—this included buildings, sidewalks, streets. Everything! Kind of amazing, really. This particular strategy does leave some issues—the space under many streets is hollow and basically unused, although maybe a creative use for it exists. It also poses challenges in planting trees and building in spaces above the tunnels since they were only designed for a specific load.
Older houses in Sacramento also often have an elevated first floor with external stairs which I find charming. Historically the first floor was used for carriages but today people either park there or store other items. So a similar strategy to what you have here, except the space is more enclosed. This works well here because the city is very flat, so even during floods there is little current. Areas with hilly topography or with coastal flooding need open space on the lower floor to allow moving water to pass under without damaging the structure.
I would also look into “sponge city” concepts with bioswales, rain gardens, etc. Another possible source of inspiration is the chinampas agricultural system in Mexico. This is an extremely productive agricultural system created by alternating deeper ditches/canals with elevated areas. This allows for more ecological diversity to grow different crops. While I don’t think it’s wise to convert existing swamps to this system due to their imperiled status, swamps aren’t particularly hospitable to have in our cities, so this could be another possible strategy to deal with seasonal flooding in existing settlements.
Climate-induced flooding is going to be a major challenge in the future and I think we’ve really only begun to reckon with this new reality.