Research Outline

Development of new indices of water resource consumption
and their application to evaluation of agricultural production

 Water use in paddy rice production were evaluated on the basis of differential water footprint (DWF), which had been developed for continuous evaluation of water use on the burden to water resource and its sustainability. Water resource should be analyzed in flow base due to its characteristics: the difficulty in controlling the supply rate, economical difficulty of transportation, and rapid regeneration. However, essential water stress is difficult to evaluate in flow base. Particular water use does not directly mean the water stress because its timing and speed is not essential, in other words, it could be later and slower without any problems. We newly introduced a concept of “acceptable delay” which is defined for each water use. It is a time period within which water can be consumed without problem. We assumed the amount of water is consumed throughout acceptable delay, and regarded this rate as the essential flow of water use. The ratio of this water flow to total supply flow in objective basin is defined as water stress. Furthermore, we defined the area as DWF in which the demand of water use flow is met by precipitation. This index enables regional accumulation and consideration of total sustainability with water resource. By integrate DWF with respect to time, total burden to water resource is obtained corresponding to each water use as stock. We name it integral water foot print (IWF) and it has unit of area multiplied by time.
 As a case study, we evaluated water use of rice production in paddy field of south area in Ibaraki prefecture, Japan. Water use in agriculture has possibility of temporal rise in water stress due to its large seasonal variation. In particular, rice is the largest water consuming sector in Japanese agricultural production. In the evaluation, we constructed scenarios of rice production on the basis of standard schedule recommended by Ibaraki prefecture, meteorological data and phenological model. Water use was estimated by simulation along the scenario. From the results, DWFs were derived for several years and analyzed the water consumption and its sustainability, comparing annual values of DWF and IWF.
 Water resource management will be more important and difficult across this century, and these indices proposed in this study are expected to contribute to more precise discussions in water resource, burden of water consumption, and their sustainability.