Kenji Tsuruta, Yoshiko Kosugi, Masanori Katsuyama, Ken’ichirou Kosugi, Masakazu Suzuki, Makoto Tani
Received 2019/10/03, Accepted 2019/12/15, Published 2020/01/18

Kenji Tsuruta¹⁾, Yoshiko Kosugi¹⁾, Masanori Katsuyama²⁾, Ken’ichirou Kosugi¹⁾, Masakazu Suzuki³⁾, Makoto Tani⁴⁾

1) Graduate School of Agriculture, Kyoto University, Japan
2) Graduate School of Life and Environmental Sciences, Kyoto Prefectural University, Japan
3) Graduate School of Agricultural and Life Sciences, The University of Tokyo, Japan
4) University of Human Environments, Japan

We quantified long-term trends in evapotranspiration, runoff, and deep percolation using 40 years of hydrological data, examining the effects of evapotranspiration on runoff during forest development in a coniferous species. Using the flow duration curve, we evaluated the effects of evapotranspiration on the entire range of flow stages (high to low flows). During the 40-year forest development, deep percolation ranged from 97 mm to 105 mm. Annual evapotranspiration increased by 623–766 mm, which appeared to be caused by increased air temperature as well as forest development. Annual runoff consequently decreased by 937–777 mm. In particular, pronounced decreases in daily flow were found with an exceedance probability of >11% in the flow duration curve. Long-term effects of evapotranspiration on runoff during forest development continued for a longer period than predicted by previous catchment studies of ~20 years duration. Our results suggest that the long-term patterns of evapotranspiration and runoff during forest development would differ from those reported by previous catchment studies under climate warming conditions and highlight the need for further research into separating the effects of forest development and increasing air temperature on evapotranspiration in long-term hydrological data.

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