Abstract
In this study, a quantitative impact assessment method was developed in order to predict the potential impact of climate change on agricultural water uses. The methodology of this assessment consists of downscaling and bias correction techniques of climate projections from Global Climate Models (GCMs), and a distributed hydrological model incorporating various paddy water uses. This hydrological model estimates the cropping area of rice paddies, the water requirements of paddy fields, diversion water at main irrigation facilities and irrigation water allocation for each paddy field as well as actual evapotranspiration, soil water content and runoff amount. We applied a series of developed methods to the Seki River Basin, an irrigation-dominant basin that experiences heavy snowfall, and carried out the experimental impact assessment of climate change on irrigation water. The results show that snow water equivalents and snowmelt were projected to decrease due to temperature rises in future periods. Consequently, this brought about a decline in river discharge, reservoir storage, and agricultural water intake amounts at diversion weirs during snowmelt seasons. In addition, the decrease in diverted water at irrigation weirs caused the shortage of irrigation water in lower areas of irrigated paddies. These results indicated that the assessment method developed in this study predicts the quantitatively explicit impacts of climate change on agricultural water uses.
