ASSESSMENT OF CLIMATE IMPACTS ON STREAM TEMPERATURE AND SWEETFISH ECOLOGY IN THE KAKO RIVER, JAPAN

Abstract

 Future climate change will impact river discharge and its temporal variation as well as biological processes in rivers due to change in temperature. This study incorporated a water temperature model into the Rain-fall-Runoff-Inundation (RRI) model developed by ICHARM, PWRI of Japan and estimated temperature distribution in the Kako River basin, Japan using a model output from a climate model of Japan Meteorological Agency. Additionally, we evaluated the effects of climate change on the habitat and upward migration timing of sweetfish. The incorporated model showed a good performance in the current water temperature simulation by comparing the daily mean and seasonal variations in the river. Water temperature from 2077 to 2095 was projected to increase in annual mean by 2.1°C and by 2.9°C in July compared with those from 1981 to 1999. However, because August precipitation in the future is greater than now, the increase in water temperature by 1.3°C became smaller than July. This increase reduced the habitat area of sweetfish. The stream length where the water temperature more than 28°C lasts 200 hours or longer increased from present 4.3% of the total length to 12.2% in the future. The upstream migration of sweetfish at the river mouth, which peaked in mid-March currently, was estimated to start earlier and peak in late February.