Abstract
Air temperature elevation in the next century by greenhouse effect has been predicted. However, the effect of the temperature increase on irrigation requirement of rice cultivation is not obvious. The objectives of this study were to estimate the evaporative demands and changes of evapotranspiration (ET) in rice in Shimane prefecture, in the cases when the daily mean air temperature increases by 1〜5℃ from the average of ordinary years. The changes of air humidity were empirically estimated from air temperature and precipitation of past decade, and ET were estimated from the Penman equation. The possibility of water shortage was the highest in August due to high evaporative demands and low precipitation. The ET was predicted to increase 3% by 1℃ increment of air temperature from average of ordinary years, 8% by 3℃ and 14% by 5℃, respectively. When the rice produce average yield (476g m^<-2>) of ordinary years in Shimane prefecture, the ET was estimated from the means of harvest index, water-use efficiency and estimated saturation deficit under warming climate. The ET under the mean air temperature of ordinary years, under 1℃ increment from mean air temperature, 3℃ and 5℃ were calculated as 413mm, 459mm (1.11×413mm), 555mm (1.34×) and 682mm (1.65×), respectively. It was suggested that the maintenance and development of water resources, particularly in mountainous area, will be important under temperature elevation.
