## 2 Study Area and Spatial Data Set  
### Study Area  
The research area in this study was Okcheon-gun in South Korea. The region is geographically located in the upstream area of the Geum River basin, which is the basin of one of South Korea's four major rivers. The Geum River flows from north to south in this area. Okcheon-gun lies between 36\({}^{\circ}\)10\({}^{\prime}\)N and 36\({}^{\circ}\)26\({}^{\prime}\)N latitudes and 127\({}^{\circ}\)29\({}^{\prime}\)E and 127\({}^{\circ}\)53\({}^{\prime}\)E longitudes. Its total area is 537.06 km\({}^{2}\), of which 347.04 km\({}^{2}\) is forest land, 55.82 km\({}^{2}\) is covered by fields, 45.63 km\({}^{2}\) is used as paddy fields, and other areas occupy 88.57 km\({}^{2}\)[6]. The annual precipitation in the area is 1297.4 mm, which is nearly equal to South Korea's annual average precipitation of 1277.4 mm (1978-2007) [33]. However, due to the influence of the East Asian Monsoon climate, rainfall is intense during summer and winter, while there is not enough water during spring and autumn. This area uses approximately 45,032,000 m\({}^{3}\) of groundwater per year. Of the total consumed groundwater, 67.2% is used for living, 32.1% for agriculture, and 0.5% for industrial purposes. As a result, the Okcheon-gun uses most of the groundwater as living and agricultural part, and the GPP map of Okcheon-gun is necessary for more efficient groundwater management [51]. Geologically, this area was developed from the Okcheon era and includes the unrecorded Okcheon supergroup. It also includes the Pyeongan supergroup, Paleozoic Choseon supergroup, the Triassic and Jurassic granitic rocks, the Cretaceous sedimentary, Quaternary alluvium, volcanic rocks, and intrusive igneous rocks (Figure 1). The Quaternary alluvium was found to be distributed along the tributaries in the Okcheon area. The alluvial layers in the plain are developed in the granite area, and the basin shape is narrow downstream in the plain. The Quaternary alluvium constitutes unconsolidated clastic sediments consisting of gravel, sand, silt, and clay. Relatively, silt and clay are more thickly deposited in the plain due to river flooding. The representative geological structure of the Okcheon area shows the fault to the northwest of the Okcheon. It also shows the thrust fault in the Okcheon and Choseon supergroup, located over the upper Pyeongan Supergroup. The thrust fault developed in the northeast and south-northwest directions [7]. A strike-strip fault exists to the northwest of the Okcheon fault which occurs across Jurassic granite rocks, the Okcheon supergroup, the Paleozoic sequence, and the Triassic granite rocks. It stretches to tens of kilometers from the west side (Figure 1). Figure 1: Study area (**a**) and geological map (**b**). and all detailed experimental procedures and results are reported in the national groundwater survey report [7]. The groundwater productivity data used in this study were converted into the binary form, where 1 is displayed when there is more than a median value of groundwater productivity, and 0 is displayed otherwise. The split criterion was T (2.6 m\({}^{2}\)/day) and the corresponding SPC (4.88 m\({}^{3}\)/day/m), which is the median of the two values. In the present study, we applied T and SPC to the three models. 18 various topographical factors were used for GPP analysis, including terrain and surface data derived from remote sensing images. (Figure 2). The selected factors were slope gradient, relative slope position, plan curvature, hydrogeology, hydraulic slope, distance from faults, distance from lineament, depth of groundwater, distance from channel network, lineament density, valley depth, Topographic Wetness Index (TWI), slope length (LS) factor, drainage basin, Terrain Ruggedness Index (TRI), convergence index, land-cover, and soil texture. The spatial database of these factors was reproduced using the ArcGIS software with SAGA-GIS.