Most flour-type adhesives (wheat, rice, potato) are all hygroscopic, meaning that they absorb water well.  Unfortunately, even if they dry out well, when subjected to moisture in the air, they get damp again.  In your climate, they would all end up getting moldy.

One organic material that Jackie says doesn't do that is the cellulose adhesive called methylcellulose.  One fairly common form of it is cellulose wallpaper paste.  You can get it wet initially, but then when it dries, it doesn't re-absorb moisture.

Quick note:  there are three general types of wallpaper pastes:  flour, cellulose and vinyl.  Make sure you get the cellulose type, it should say on the container.  It should mix clear, not milky like the flour pastes.

Make the mix fairly thin, about the consistency of raw egg whites.  Put some water in a container and sprinkle some of the cellulose adhesive onto the water and mix in.  Some mix well, others seem to clump so leave overnight to absorb water, stirring occasionally.  Only mix the amount you think you'll need, as it doesn't keep well (it loses it adhesiveness).

Vary the amount of dry cellulose to water to get the affect that is best for your purposes.

Sue