[A-HW18] Material transportation and cycling at the land-sea interface: from headwaters to the ocean

[AHW18-P04] Spatial and Temporal Water Balance in a Forested Catchment in Western Japan Using the SWAT Model

*Rendilicha Halake Guyo¹, Kunyang Wang², Mitsuyo Saito², Shin-ichi Onodera², Sharon Bih Kimbi², Nang Yu War², Yuta Shimizu³, Toshitsugu Moroizumi¹ (1.Graduate School of Environmental and Life Science, Okayama University, 2.Graduate School of Advanced Science and Engineering, Hiroshima University, 3.Western Region Agricultural Research Center, National Agriculture and Food Research Organization)

Keywords:SWAT model, Water balance, Spatial and temporal variation, Forested catchment

Evaluating the key components of a catchment's hydrologic water balance is crucial for understanding water resource availability for human activities. To accomplish this, this study employs the use of the Soil and Water Assessment Tool (SWAT) model in the Asahi River catchment, located in the western Japan. The model was used to analyze various factors such as evapotranspiration, surface flow and groundwater recharge to estimate the amount and variability of water available for consumption, as well as identify potential water shortages or excesses. Additionally, the model was used to quantify the interactions between climate condition, land use practices, reservoir management and water supply over a decade simulation period. The model's reliability and applicability were assessed through multiple site calibration and validation with observed streamflow data. The comparison of measured and simulated streamflow data showed reasonable interactions and outputs for each water budget component. Spatial variations in the correlation between precipitation and groundwater recharge were observed in the catchment, with higher levels of both variables detected in the upper catchment and a gradual decrease in both variables as we move downstream. In terms of seasonal patterns, the upper catchment experienced the highest levels of precipitation during autumn, while the lower catchments had the highest levels of precipitation during summer. Despite the seasonal differences in precipitation, both shallow and deep aquifer recharge in the catchment is highest during autumn due to the elevated levels of rainfall and decreased evapotranspiration. Given its dominance in the catchment, the forest appears to be a reservoir for both shallow and deep aquifer recharge. However, further detailed investigations are necessary to accurately quantify the extent to which the forest acts as a natural dam and the specific mechanisms involved.

Acknowledgments
This research was supported by JSPS Grant-in-Aid for Scientific Research (B) (No. 21H03650, PI: Mitsuyo Saito) and Fostering Joint International Research (A) (No. 20KK0262, PI: Mitsuyo Saito).