5:15 PM - 6:30 PM
[AHW21-P03] Regional climate change impacts on groundwater level in the Kurobe River alluvial fan, Japan
The purpose of this study is to clarify the impact of climate change on the groundwater level in the Kurobe River Alluvial Fan. It has been pointed out that the temperature is on the rise due to climate change, and that the form of precipitation in the future will change from snowfall to rainfall. As a result, water supply from snow cover will decrease and the peak period of river flow will be earlier. Groundwater is also predicted to change its peak groundwater level in the same way as river flow. Increased rainfall is predicted to increase winter recharge and raise the groundwater level. This study evaluates the effects of climate change on the water balance and fan groundwater level in the Kurobe River basin using the RCP8.5 scenario.
The meteorological data used were precipitation, temperature, and solar radiation which used was the NIES statistical downscaled 1 km mesh data provided by the National Institute for Agro-Environmental Sciences. The analysis was conducted for the historical climate (1981-2000) and the end of the 21st century (2081-2100). This study was developing a model that combines a distributed water balance model and a groundwater analysis model (Dtransu), and conducted numerical experiments. The snowfall rate was calculated as 100% for temperatures below 0 ℃ and 0% for temperatures above 4.5 ℃. The snowfall rate between 0 and 4.5 ℃ was approximated by a linear line, and the amount of snowfall and rainfall was calculated by multiplying the amount of precipitation by the snowfall rate. The validity of the model was evaluated based on the river flow rate at the observation points where no water engineering facilities exist in the upstream area, 18 groundwater level stations located in the alluvial fan area, and the groundwater residence time calculated from the tritium analysis results. As a result, the flow rate of the river and the residence time of the groundwater were generally the same and could be reproduced. On the other hand, the groundwater level could not be reproduced at all stations, but the contour map of the groundwater level in the whole alluvial fan area could be reproduced.
As a result of the increase in temperature, it was found that at the end of the 21st century, the amount of snow water equivalent would decrease by 23 % (260 mm) compared to the historical climate, and the snow disappearance period would end one month earlier than the historical. As a result, the water balance of the Kurobe River basin showed that the peak of surface runoff and infiltration in the late 21st century was projected to be one month earlier than historical, and the surface runoff and infiltration increased from November to February. The groundwater level in the alluvial fan area increased during January to March and decreased during May to July. The results suggest that the current water system may not be able to provide sufficient water supply during the cultivation period, because climate change causes a decrease in surface runoff and groundwater level during the cultivation period from May to June.
The meteorological data used were precipitation, temperature, and solar radiation which used was the NIES statistical downscaled 1 km mesh data provided by the National Institute for Agro-Environmental Sciences. The analysis was conducted for the historical climate (1981-2000) and the end of the 21st century (2081-2100). This study was developing a model that combines a distributed water balance model and a groundwater analysis model (Dtransu), and conducted numerical experiments. The snowfall rate was calculated as 100% for temperatures below 0 ℃ and 0% for temperatures above 4.5 ℃. The snowfall rate between 0 and 4.5 ℃ was approximated by a linear line, and the amount of snowfall and rainfall was calculated by multiplying the amount of precipitation by the snowfall rate. The validity of the model was evaluated based on the river flow rate at the observation points where no water engineering facilities exist in the upstream area, 18 groundwater level stations located in the alluvial fan area, and the groundwater residence time calculated from the tritium analysis results. As a result, the flow rate of the river and the residence time of the groundwater were generally the same and could be reproduced. On the other hand, the groundwater level could not be reproduced at all stations, but the contour map of the groundwater level in the whole alluvial fan area could be reproduced.
As a result of the increase in temperature, it was found that at the end of the 21st century, the amount of snow water equivalent would decrease by 23 % (260 mm) compared to the historical climate, and the snow disappearance period would end one month earlier than the historical. As a result, the water balance of the Kurobe River basin showed that the peak of surface runoff and infiltration in the late 21st century was projected to be one month earlier than historical, and the surface runoff and infiltration increased from November to February. The groundwater level in the alluvial fan area increased during January to March and decreased during May to July. The results suggest that the current water system may not be able to provide sufficient water supply during the cultivation period, because climate change causes a decrease in surface runoff and groundwater level during the cultivation period from May to June.