Response of hydrological processes to climate and land use changes in Hiso River watershed, Fukushima, Japan

Abstract Hiso River watershed (HRW) is within a radiocesium contaminated area caused by the disaster in Fukushima Daiichi nuclear power plant (FDNPP). The FDNPP accident resulted in enormous changes in land use in HRW. It's urgently needed to evaluate impacts of climate and land-use changes on hydrological process, which further control pollutants transport in HRW. A combination method of Statistical DownScaling Model (SDSM) and Soil and Water Assessment Tool (SWAT) was applied to generate future climatic and hydrologic variables. Future climate data was obtained from three Representative Concentration Pathway (RCP2.6, 4.5 and 8.5) scenarios of a single General Circulation Models in three future periods of 2030s, 2060s and 2090s (2010–2039, 2040–2069, 2070–2099), with a baseline period (1980–2009). According to land-use change in HRW during 2013–2017, three land-use change scenarios under the three future climate scenarios were established. Results suggested that SDSM showed good capabilities in capturing daily maximum/minimum temperature and precipitation. The SWAT model presented good performances in simulating monthly and yearly streamflow. Results also suggested projected higher temperatures and lower rainfall led to decreased annual water yield and evapotranspiration (ET). The annual water yield and ET decreased in most seasons while had a slight increase in spring. RCP8.5 scenario always generated larger magnitudes for climatic variables and water balance components compared with other climate scenarios. Land-use changes had strong impact on surface runoff and groundwater flow. These results emphasize the necessity of considering impacts of climate and land-use changes on hydrological processes when making decontamination policy in radiocesium contaminated areas.