杉浦 未希子

Water scarcity is a social and relative concept that necessitates considering the social and technological factors that determine the quantity and quality of water demand and supply. Thus, institutional responses to water scarcity are diverse and dynamic, reflecting climatic and geographical conditions. In the case of Japan, located in monsoon Asia and experiencing irregular rainfall and drought with a certain probability, a water use order has been formed based on the river-water use for irrigation as a stable source. In terms of increasing supply, modern advances in engineering technology has made it possible to augment river flows by releasing water stored in multipurpose dams, which has enabled the establishment and operation of the modern permitted water rights system, and a new water use order and its adjustment. The "drought coordination" (Kassui-chōsei) is an example of such a system, which was institutionalized in anticipation of voluntary coordination among water users due to the functions of multipurpose dams and the existence of river administrators. Although river water is "public water" and not subject to trade along with water rights, the implementation of various administrative strategies to create new water rights have also contributed to alleviating conflicts caused by social water shortages. In terms of reducing demand, field-based irrigation commons still play an essential role. Block rotational irrigation efficiently reduces demand as part of the nesting structure implemented by LID, a traditional mura-based Water Users Association. It implements a determined rate of water conservation through effective and efficient water management as part of the structure.