Assessing the Impact of Spatial Accuracy of Digital Elevation Models on Simulating Discharge in Arid Regions Using SWAT Model: A Case Study of the Lar Watershed

Aims: The Digital Elevation Model (DEM) plays a crucial role in the SWAT model and significantly impacts its output results. This study evaluated the effect of different spatial accuracy of DEM in runoff simulation using the SWAT and SWAT-CUP models for the Lar Watershed in Sistan and Baluchestan Province. Materials & Methods: This study examines the impact of different accuracies of Digital Elevation Models (DEMs) with resolutions of ۱۲.۵, ۳۰, ۵۰, ۹۰, ۴۵۰, and ۱۰۰۰-meters on discharge simulation using the SWAT model for the Lar Watershed, located in an arid region. The model was selected for ۳۰ years (۱۹۸۸-۲۰۱۷), with ۱۸ years for the calibration period and ۱۲ years for validation. The SWAT-CUP software and the SUFI-۲ method were used. The model’s accuracy was also evaluated using the Nash-Sutcliffe efficiency (NS), coefficient of determination (R²), r, and p coefficients. Findings: The discharge simulation results reveal that variables such as area, sub-basin, Hydrologic Response Unit (HRU), watershed slope, and mean channel slope are particularly affected by DEM accuracy. With increasing DEM accuracy, the length of the main channels decreases, and lower-order channels are eliminated, reducing the calculated discharge depth. Our sensitivity analysis identified seven key parameters influencing discharge simulation in the Lar Watershed. The most critical parameters were r__CN۲.mgt, v__ALpha_BF.gw, and r__SOL_AWC.sol, consistently recognized as highly sensitive in similar studies. Conclusion: During validation and calibration, DEM resolutions of ۱۲.۵ and ۱۰۰۰ meters exhibited lower accuracy than those of ۳۰, ۵۰, ۹۰, and ۴۵۰ meters, suggesting that extremely high or low spatial data accuracy does not enhance simulation accuracy. Additionally, minimal differences were observed among the results for DEM resolutions of ۳۰, ۵۰, ۹۰, and ۴۵۰ meters. This can be attributed to adjustments in calibrated variable values and the application of the SUFI-۲ method across different DEM accuracies. Finally, based on the results of this research, the DEMs with spatial resolutions of ۳۰, ۱۲.۵, ۵۰, ۹۰, ۴۵۰, and ۱۰۰۰ meters demonstrated the best performance for simulating monthly discharge in the Lar Watershed. Additionally, based on the value of the objective function (NS) during the calibration and validation stages, it can be concluded that the SWAT model can simulate the monthly discharge of the Lar Watershed with acceptable accuracy. Therefore, it can be said that the SWAT hydrological model can be used in arid regions to implement management scenarios quickly and at a low cost for decision-making.

کلیدواژه ها:

SWAT-CUP ، DEM ، SUFI-۲ method ، Nash-Sutcliffe efficiency ، SWAT hydrological model