Accompanied by climate change due to global warming Prediction of changes in the flow conditions of the Yamato River system

Climate change due to global warming will cause extreme rainfall and flood damage in many areas. On the other hand, increased evapotranspiration due to rising temperatures may lead to more frequent droughts. The Yamato River, a first-class river originating in Nara Prefecture and flowing through the Osaka Plain in Japan, has historically been a serious water shortage. In this study, we considered the changes in the flow conditions of the Yamato River using the large ensemble data d4PDF. For the simulation, we used a distributed runoff model that has been modified to take into account intake and wastewater by the artificial system and water supply from other basins (the Kinokawa River basin). we used The +4K climate simulation data (60 years x 90 ensembles) and the Historical climate simulation data (30 years x 50 ensembles) from d4PDF as input values to simulate the long-term flow conditions of the Yamato River. Also, The Yamato River system experienced a major drought event in 1994, and we organized the evapotranspiration relative to the flow conditions(Fig. 1) and water temperature (Fig. 2) for ensembles below the total annual rainfall and total annual runoff in 1994. Fig. 1 shows computation results such as the historical experimental values(1), the experimental values(2) for a 4°C increase and the experimental values(3) for a 4°C increase in natural flow conditions (without water supply from the Kinokawa River basin). The results show that evapotranspiration will become more dominant to the runoff volume in the basin in the future due to the increase in evapotranspiration. In addition, from Figure 2, water temperature generally follows air temperature, although the degree and variability of water temperature increase vary depending on the influence of intake and wastewater at each site. Furthermore, a comparison them with the simulation results using the actual values for 2004-2007 and 2011 as input values shows that the water temperature will also increase with the future rise in air temperature.