Rainfall varies considerably in the Shinano basin. In the middle part of the Chikuma River, near its confluence with the Sai River, rainfall is some of the lowest in Japan, generally staying below . The low precipitation is primarily due to its encirclement by the three ranges which make up the Japanese Alps and by the Jōshin'etsu-kōgen National Park. However, the upper reaches of the Chikuma and Sai Rivers and the lower part of the Chikuma River (where it changes name to the Shinano River) receive annually. In the central areas of the Shinano River, especially in the Uono Basin, precipitation increases to around ; this area receives some of the highest winter snow falls in Japan with 40-50% of this precipitation falling as snow. The heavy snow melt is responsible for much of flooding to affect the Echigo, but also allows for the hydroelectricity generation and regular irrigation.