Possible hydrological effect of rainfall duration bias in dynamical downscaling

Abstract

: Motivated by the problem of rainfall duration bias typi‐ cally found in dynamical downscaling, its possible effect on hydrology was evaluated for heavy rainfall events over Kyushu, Japan, during summer. Heavy rainfall in western Kyushu is often related to a persistent Baiu rainband across Kyushu, while in eastern Kyushu it is related to the passage of typhoons near Kyushu. For typical heavy-rainfall peri‐ ods, we ran a tank model for several target rivers to analyze runoff and water-depth sensitivity to the hyetograph by arti‐ ficially extending the rainfall duration to 8 hours while maintaining the same total rainfall. This showed that a spike in peak runoff was suppressed by prolonged weak rainfall as typically found in downscaling outputs. The tim‐ ing of rising runoff and water depth in the tank model was shifted earlier.