Optimizing Outflow Simulations Using the SWAT Model in a Small Watershed with Scarce Discharge Observations: A Methodological Approach

초록

Understanding how water moves through a landscape is essential for managing water resources, especially in small areas where direct measurements are scarce. In this study, we used the soil and water assessment tool (SWAT) model to estimate how much water flows out of a watershed using limited data. Our analysis included information on land use, soil type, and weather patterns from 2021 to 2024, helping us account for changes in rainfall, including extreme weather events. Over these four years, the area received an average of 1,481 mm of rainfall per year, with 397 mm running off the sur face. The total amount of water flowing out, including underground water movement, was estimated at 711 mm per year, which made up about 48% of the total rainfall. To improve accuracy, we adjusted CN2, SOL_K, and ALPHA_BF key model settings related to how water moves through the soil and how streams are fed by underground sources. The model showed that underground water movement varied throughout the year, with the lowest values in April (9 mm) and the highest in August (39 mm), reflecting wetter conditions. Water lost through plant use and evaporation also changed with the seasons, reaching its peak in July (115 mm) and dropping to its lowest levels in winter (17 mm in January and December). When we compared the model’s predictions with actual data, the results showed a strong match. The model slightly underestimated water flow in October 2024, but overall, it provided reliable estimates. Despite the limited data, our findings show that this approach is useful for understanding water flow in small watersheds and can support better planning for water use and flood prevention.

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