2020 年 8 巻 1 号 p. 234-240
We developed a new surface flow direction dataset named “Japan Flow Direction Map (J-FlwDir)” at 1-sec (~30 m) resolution for the entire Japan domain, using “Kiban Chizu Joho” digital elevation model and “Kokudo Suchi Joho” water body layers. The calculation of flow directions for a large domain used to be difficult due to errors in the input elevation data. We solved this problem by developing a new algorithm, which first calculates the initial-guess flow directions by the steepest slope method, and then ensures river connectivity by reversing the initial-guess flow directions when needed. The new flow direction data shows better consistency with the actual river networks compared to the previous HydroSHEDS flow directions. We also generated supplementary data layers such as flow accumulation area, adjusted elevation, and river width. The new flow direction dataset will be published online, and is expected to enhance any geoscience studies which rely on flow direction data.