## 2 Materials and Methods
### Data  
#### 2.2.1 Digital Elevation Models  
Nine publicly available global DEMs listed in Table 1 were evaluated in the study area to select a base 1\({}^{\prime\prime}\) DSM for the computation of CRDTM2020. First, 1\({}^{\prime\prime}\) DEMs: SRTMGL1, NASADEM, and AW3D30 and ASTER DEMs were evaluated. The SRTMGL1 DEM [18] was first released for the USA and then became the most-used global publicly available 1\({}^{\prime\prime}\) DEM. This model is also referred to as SRTM Version 3.0 Global 1 arc second. NASADEM [19] is a 1\({}^{\prime\prime}\) DEM released in February 2020 and is expected to have better accuracy than SRTMGL1 due to improvements in processing, such as void reduction, gap-filling procedures, vertical adjustments using ICESat laser profiles, and improved quality assessments and adjustments [20; 21]. The AW3D30 DEM [22; 23] is the ALOS World 3D-30m (AW3D30) DSM dataset from the Japan Aerospace Exploration Agency (JAXA). The 5 m mesh size AW3D is not available to the public; therefore, only the freely available 1\({}^{\prime\prime}\) Version 3.1 released in April 2020 was downloaded from [[https://www.eorc.jaxa.jp/ALOS/en/aw3d30/data/index.htm](https://www.eorc.jaxa.jp/ALOS/en/aw3d30/data/index.htm)]([https://www.eorc.jaxa.jp/ALOS/en/aw3d30/data/index.htm](https://www.eorc.jaxa.jp/ALOS/en/aw3d30/data/index.htm)) (accessed on 16 November 2020) for evaluation. The data for the DEM are from an optical sensor, the Panchromatic Remote-sensing Instrument for Stereo Mapping (PRISM) aboard the Advanced Land Observing Satellite (ALOS) operated from 2006 to 2011. ASTER GDEM 003 [24] stands for Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model Version 3. This version of the 3\({}^{\prime\prime}\) DEM was released in August 2019 by the National  
Figure 1: (**a**) Topography of the study area represented by 1\({}^{\prime\prime}\) NASADEM. (**b**) Slopes in degrees computed from NASADEM. (**c**) Histogram of the NASADEM elevation distribution in the study area. (**d**) Histogram of the distribution of slopes in the study area. Aeronautics and Space Administration (NASA) and the Ministry of Economy, Trade, and Industry (METI) of Japan. Stereo image data for GDEM 003 were acquired between March 2000 and November 2013 by the ASTER instrument aboard NASA's Terra spacecraft. In order to compare global DTMs to CRDTM2020, two 3\({}^{\prime\prime}\) DTMs were evaluated: MERIT DEM and BEST DEM, as well as their base DEMs, SRTM3 and SRTM v4. SRTM3 DEM v003 [25] is a 3\({}^{\prime\prime}\) DEM produced by NASA, also called void-filled \"SRTM Plus\", SRTM NASA V3, or SRTMGL3S DEM. It used SRTM V2, where the radar interferometric method was successful (no voids), and most voids were filled with ASTER GDEM2 (Global Digital Elevation Model Version 2) data. The SRTM v4.1 DEM [26] is a 3\({}^{\prime\prime}\) DEM from the CGIAR Consortium for Spatial Information ([[http://srtm.csi.cgiar.org](http://srtm.csi.cgiar.org)]([http://srtm.csi.cgiar.org](http://srtm.csi.cgiar.org)), accessed on 4 April 2020). We advise any future user to check the _.tfw_ files of the DEM tiles for correct registration. The MERIT DEM [4] (available at [[http://hydro.iis.u-tokyo.ac.jp/~yamadai/MERIT_DEM](http://hydro.iis.u-tokyo.ac.jp/~yamadai/MERIT_DEM)]([http://hydro.iis.u-tokyo.ac.jp/~yamadai/MERIT_DEM](http://hydro.iis.u-tokyo.ac.jp/~yamadai/MERIT_DEM)), accessed on 5 June 2020) is currently the most commonly used global DTM. It was computed from the SRTM3 v2.1 DEM and AW3D30v1 DEM in high latitudes by a four-step elimination of absolute bias, stripe noise, tree height bias, and speckle noise. The BEST DEM [2,27] stands for Bare-Earth SRTM Terrain. It is a vegetation-removed DTM from the gap-filled SRTMv4. In addition, the 3\({}^{\prime\prime}\) version of the TanDEM-X DEM was added.