Question about the impact of high-resolution LIDAR DEM in SWAT+

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Iman Soukrate

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May 6, 2025, 9:11:26 AM5/6/25

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Dear SWAT+ team,

I am reaching out to you as part of a research project focused on the potential of Nature-Based Solutions to enhance groundwater recharge in regions experiencing high water stress.

In this project, we implemented a methodology based on hydrological modeling using SWAT+, via the QSWAT+ interface. In the first phase, we calibrated the model using a standard-resolution DEM (25 m), land use data, and soil maps, and simulated several intervention scenarios (wetland restoration, reforestation, and infiltration systems).

In the second phase, we plan to use a high-resolution DEM derived from LIDAR data, along with multispectral analyses to better characterize vegetation cover and soil moisture. The goal is to apply the same methodology with more detailed input data in order to identify optimal locations for groundwater recharge more precisely.

However, we have the following question:
Based on your experience, does a significant improvement in DEM resolution (e.g., from 25 m to 1 m) have a real impact on SWAT+ model outputs, particularly for groundwater recharge estimation? Is it technically feasible and relevant to use a high-resolution LIDAR DEM in QSWAT+, or does the model structure limit the benefits of such increased precision?

During the workshop, I understood that DEM resolution might not significantly influence model results, and that Hydrological Response Units (HRUs)—defined by land use, soil texture, and slope—play a more decisive role. Could you confirm whether HRUs are generated based on pixel-wise combinations of the input maps? And if so, could a higher-resolution DEM indirectly affect HRU delineation through improved slope representation?

Thank you in advance for your insights and for developing such a valuable tool for hydrological research.