HIGH-RESOLUTION FLOW DIRECTION MAP OF JAPAN

We developed a new surface flow direction datasets at 1-sec (~30m) 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 a new algorithm, which first calculate the initial-guess flow directions by a steepest slope method, and then ensure river connectivity by reversing the initial-guess flow directions when needed. The new flow direction data shows better consistency to the accrual 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 datasets will be published online, and considered to advance any geoscience studies which relies on flow direction data.