1. Terrain data

    (1) MERIT Hydrological Map: obtained from the MERIT Hydro dataset, which is a 90 meter resolution global dataset using WGS84 and EGM96 geodetic reference frames, with a spatial resolution of 3 arc seconds (approximately 90 meters at the equator);

    (2) HydroBASINS Global Watershed: Watershed boundary data from the three-level HydroBASINS dataset was applied, which is a multi-level global watershed dataset derived from SRTM DEM data;

    (3) MERIT Basins is a global vector hydrogeology database derived from the 90 meter MERIT Hydro product, based on a drainage threshold of 25 square kilometers.

    2. Reference and benchmark datasets

    (1) JRC Flood Map: The flood hazard map drawn by the European Commission JRC has been selected as part of the reference and validation dataset, covering the period from 1980 to 2013, with a resolution of 0.1 °;

    (2) GAR Flood Map: The GAR of the United Nations Office for Disaster Risk Reduction (UNDP) and CIMA Foundation selected the 500 year flood map of the hydrodynamic model as the reference and validation dataset. The characteristics of this dataset are a recurrence interval of 25, 50, 100, 200, 500, and 1000 years, covering the range from 60 ° N to 60 ° S latitude, with an original resolution of 90 meters for SRTM DEM and later summarized as 1 kilometer;

    (3) GFPLIN250m Flood Zone Map: The GFPLIN250m Flood Zone Map was used as a benchmark and another validation dataset with the same coverage as GAR;

    (4) Global Lakes and Wetlands Dataset (GLWD) Lakes and Reservoirs Dataset: Using the Global Lakes and Wetlands Dataset (GLWD) jointly developed by the World Wildlife Fund (WWF) and the Environmental Systems Research Center at Kassel University, this dataset references data from multiple sources and is further refined through independent data from the United States Geological Survey and extensive visual and quality control.

    3. Related datasets

    (1) Global Drought Index Database: Use the Drought Index (AI) from the Global Drought Index and Potential Evapotranspiration Database (Global-AI-PET-v3) to evaluate its association with FHG parameters. This database provides global potential evapotranspiration (ET0) and AI data for 30 arc seconds;

    (2) Leaf Area Index Climatology: Provides a gridded monthly average leaf area index of 0.25 °× 0.25 ° globally, with an average value from August 1981 to August 2015.

    In FHG, the optimized empirical index b shows a statistically significant positive correlation with hydrological and climatic conditions, especially in the main watersheds. Based on the proposed framework, we created a global geomorphic floodplain map called SHIFT (Improving Spatial Heterogeneity of Floodplain through Terrain Analysis) using terrain input from the 90 meter MERIT hydrological dataset. The results showed that SHIFT can effectively capture the global patterns and regional details of geomorphic floodplain. The following points demonstrate the effectiveness of our framework:

    The relationship between these parameters and hydroclimatic variables (such as AI, LAI) is statistically significant but relatively weak, indicating an enhanced representation of spatially heterogeneous hydrological and geomorphological information at the watershed level.

    The filtered data conforms to a relatively stable power law, indicating that the proportional relationship of regionalization is very robust.

    The change in parameters has improved consistency with existing maps, better distinguishing between the main streams and tributaries in the main watershed, and more comprehensively reflecting the stream network in the aggregated watershed.