[A-HW22] Material transportation and cycling in watershed ecosystems; from headwaters to coastal areas

[AHW22-15] Water discharge at forested watersheds throughout Japan by using SWAT

*Naohiro Imamura¹, Kunyang Wang², Shin-ichi Onodera², Yuta Shimizu³, Masahiro Kobayashi¹, Takanori Shimizu¹, Naoyuki Yamashita¹, Yoshiki Shinomiya¹, Koji Tamai¹, Shinji Sawano¹, Shin'ichi Iida¹, Naoki Kabeya¹, Akira Shimizu¹, Yoshio Tsuboyama¹ (1.Forestry and Forest Products Research Institute, 2.Hiroshima University, 3.National Agriculture and Food Research Organization)

Keywords:Water discharge, SWAT, Forested watersheds

Predicting the impact of forest operations and/or climate change on water and nutrient cycle in forest watershed are more important for planning future forest management in Japan. This study estimated daily water discharge at different sizes and different climate watersheds in Japanese forested areas by using SWAT. We calculated discharge at Jyozankei (1.9 ha) in snowfall area (Abe et al., 2010; 2011; 2014; Nobuhiro et al., 2020), Katsura (60 ha) and Tsukuba (3.8 ha) in a temperate area, and Kahoku (3.7 ha) and Takatoriyama (19 ha) in heavy rainfall area. As a result, daily hydrographs showed relatively high reproduction for observed values at all watersheds (Nash-Sutcliffe efficiency (NSE) showed over 0.65 value). This means SWAT can calculate water discharge at various size forested watersheds in the Japanese climate. However, the calculated peak water values were a little low compared to the observed value. This indicated discharge in stormflow periods did not reproduce effectively. Setting distribution of soil depth in the watershed may be more important for improving water discharge in small forested watersheds.