Abstract
Abstract The main objective of this paper is to evaluate the impact of land cover resolution, in comparison with the digital elevation model (DEM) resolution, on hydrological modeling outputs. Three different basins in the various resolutions of DEM (12.5, 25, 50, 100, 500 and 1,000 m) and land-use maps (250, 1,000 and 2,500 m) were collected in this study, and the hydrological modeling process was performed using the Soil and Water Assessment Tool (SWAT) model. The soil type resolution was 1,000 m for all basins, and the runoff modeling was done based on the Soil Conservation Service Curve Number (SCS-CN) method. The final model outputs showed that the DEM cell size variations affect significantly the topographical characteristics of a catchment such as area, mean slope, river network and time to concentration which alter the flood modeling outputs especially in hilly watersheds (mean slope more than 15%) up to 15% for a DEM cell size of 1,000 m in comparison to 12.5 m. Also, the resolution and spatial distribution of land cover maps which directly specify SCS-CN values, can change the output simulated runoff results up to 49% for a land cover cell size of 2,500 m in comparison to 250 m. These results indicated that the quality of the land cover map is more important than the quality of DEM in hydrological modeling. Also, the results showed that for an identical land-use cell size, the differences between model outputs using DEM cell sizes less than 100 m were not very significant. Furthermore, in all models by increasing the DEM cell size, the simulated runoff depth was decreased.
Highlights
Hydrological models are useful to identify present and future water resources, and they help researchers and water managers to estimate the spatial variability in resource over watersheds
The most advantages of the Soil and Water Assessment Tool (SWAT) model are its ability to perform on multiple geographic information system platforms, and four major input data of this model include digital elevation model (DEM), land-use land cover (LULC), soil types and meteorology data
Liu et al ( ) implemented research in an agricultural watershed of Xiangxi River, Three Gorges Reservoir in China, with various DEM resolutions (30–1,000 m) and showed that different sediment yield and different dissolved oxygen load could be achieved especially for DEM larger than 500 m. In another river watershed in China named Xiekengxi River, Lin et al ( ) investigated the impact of DEM resolution (5–140 m) and DEM source on SWAT model outputs, and the results showed that DEM source was more important and might produce better outputs in comparison to DEM resolution
Summary
Hydrological models are useful to identify present and future water resources, and they help researchers and water managers to estimate the spatial variability in resource over watersheds. There are various physical-based models designed to simulate hydrological processes, such as Areal Nonpoint Source Watershed Environment Response Simulation (ANSWERS) (Beasley et al ), Simulator for Water Resources in Rural Basins (SWRRB) (Williams et al ), Soil and Water Assessment Tool (SWAT) (Arnold et al ), Better Assessment Science Integrating point and Nonpoint Sources (BASINS) (Whittemore ) and Hydrological Simulation Program – FORTRAN (HSPF) (Bicknell et al ). The SWAT model, which was developed in the 1990s, has broad application in hydrologic studies. It can simulate the quality and quantity of surface and groundwater including pesticide loading. The most advantages of the SWAT model are its ability to perform on multiple geographic information system platforms, and four major input data of this model include digital elevation model (DEM), land-use land cover (LULC), soil types and meteorology data. As drainage networks are the key characteristics of watershed systems and universally derived from the DEM (Shen et al ; Galoie et al ), DEM is mainly used for the extraction of physical properties (Bourdin et al )
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