Rainfall entropy for delineation of water resources zones in Japan

Daily rainfall observed at a network of 1107 raingauges in Japan is analyzed using Shannonʹs entropy (informational) theory. The uncertainty of the over-a-year rainfall apportionment is quantitatively measured by entropy and an isoentropy map for the whole country is constructed. This isoentropy map is compared with Japanʹs well-known climatic division map, and is found to be capable of satisfactorily explaining the characteristics of nationwide rainfall. When used in conjunction with an isohyetal map of the average annual rainfall, it enables a relative assessment or categorization of the potential availability of water resources.