Understanding SWAT parameter for calibration part 5

SWAT Calibration Parameters Overview
📌 The video focuses on explaining 24 sensitive parameters crucial for SWAT model calibration, which are vital for accurate hydrological simulations.
🗺️ Parameter selection depends heavily on the location characteristics, including temperature, weather, topography, land use, and soil type.
⚙️ The SWAT model simulates water by dividing the area into subbasins further subdivided into Hydrologic Response Units (HRUs).

Key Parameter Descriptions
💧 Curve Number (CN2): Represents water behavior; a low CN means high absorption (like a sponge), while a high CN indicates more surface runoff, common in paved or compacted areas.
💨 SURLAG (Surface Runoff Lag Coefficient): Dictates the time water takes to become runoff; a higher coefficient results in a longer lag time, smoothing the stream hydrograph.
💧 SWAWC (Available Water Capacity): The difference between Field Capacity and Wilting Point; increasing it boosts percolation and baseflow, decreasing surface runoff.
🌡️ PLAPS (Precipitation Lapse Rate): Allows for spatial precipitation distribution based on topography, using positive values for increased precipitation with elevation or negative for a decrease.

Groundwater and Flow Dynamics Parameters
🌊 GW_REVAP (Groundwater Revap Coefficient): Controls water movement from the soil aquifer to the root zone; increasing it enhances reevaporation from the aquifer and decreases return flow, leading to lower base flow.
⏱️ GW_DELAY (Groundwater Delay Time): The lag between water exiting the soil profile and entering the soil aquifer; high values mean longer time to reach the stream and reduced base flow.
📉 ALPHA_BF (Baseflow Recession Coefficient): Affects the time base flow takes to move from groundwater to surface water; a decrease in ALPHA_BF signifies more days required for this transfer.

Calibration Strategies and Adjustments
📈 Overestimation of Overall Flow: If the calculated flow is too high, calibration steps include decreasing CN2, increasing SWAWC, and increasing ESO.
📉 Low Base Flow and High Evaporation: To correct this imbalance, adjustments should focus on playing with parameters that influence these components as outlined in the presentation slides.
📉 Low Peak Flow: If the peak flow is too low, specific parameter adjustments (not detailed here but referenced in the video's instruction set) must be followed for calibration.

Key Points & Insights
➡️ Understanding parameter concepts is essential because skipping this step makes calibration challenging and time-consuming.
➡️ Parameters like CN2 operate at the HRU level, influencing surface runoff directly based on landscape absorption characteristics.
➡️ CHK1/CHK2 (Effective Hydraulic Conductivity) define water loss/gain (losing or gaining stream) and are measured in mm per hour.
➡️ For calibration guidance, follow the provided structure: if a specific model output (e.g., overall flow, base flow, peak flow) is too high or too low, there is a prescribed set of parameters to adjust to correct the error.

📸 Video summarized with SummaryTube.com on Jan 31, 2026, 02:59 UTC