Climatic water balance and climatic division of rice producing districts in the Chubu region, Japan

Abstract

Thornthwaite's climatic division system based on potential evapotranspiration (PE) and climatic water balance is well known. In this study, a climatic division of the rice-producing district in the Chubu region of Japan is proposed based on Thornthwaite's system. The PE and climatic water balance were calculated using 1-km mesh units on mesh climate charts derived from data acquired by the AMeDAS system. From published sources, data was gathered on the rice yields of all the municipalities in the Chubu region from 1979 to 2001, and related to the PE and climatic water balance data calculated using Thornthwaite's method. It emerged that the rice yields were optimal for an August mean PE of 140 mm and enhanced in dry conditions. Moreover, to make the climatic division, a cluster analysis was performed for each municipality using PE, the moisture index (degree of humidity derived from a water balance calculation), and rice yield data. Consequently, the Chubu region was divided into 5 categories: Wetland, Nagano basin, Mountain, Hokuriku plain, and Tokai plain. This division expresses the basic climatic features that are important to rice production. Our climatic division differs from others in that our division is based both on climatic elements, which are an origin, and on rice yields, which are agricultural outputs.