What Are The Optimal Calibration Parameters For The Soil And Water Assessment Tool (SWAT) Model To Accurately Simulate The Impacts Of Variable Agricultural Land Use Practices On Groundwater Recharge Rates In A Semi-arid Region With A Complex Geology Of Fractured Bedrock And Alluvial Aquifers?

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Optimal calibration of the SWAT model for simulating groundwater recharge in a semi-arid region with complex geology requires focusing on parameters that influence water movement through the soil and aquifer, considering the region's hydrological characteristics. Here's a structured approach:

Key Parameters for Calibration:

  1. Curve Number (CN): Adjust to reflect surface runoff potential, considering soil moisture and surface conditions.
  2. Available Water Capacity (AWC): Calibrate to accurately capture soil water retention and recharge.
  3. Baseflow Alpha Factor (ALPHA_BF): Adjust to represent the rate of water release from the aquifer, potentially lower for fractured bedrock.
  4. Groundwater Delay (GW_DELAY): Increase to account for slower recharge and contribution to streams in semi-arid conditions.
  5. Elevation (ELEV): Consider its impact on water table depth and flow.
  6. Rooting Depth (DD, DDP): Adjust based on agricultural practices to reflect water uptake by plants.
  7. Groundwater Revap Coefficient (GW_REVAP): Calibrate to account for water moving back to the soil in dry conditions.
  8. Hydraulic Conductivity (HYD_K): Set higher for fractured bedrock and lower for alluvial aquifers.
  9. Deep Aquifer Percolation Fraction (DP): Adjust based on local hydrology and evapotranspiration rates.
  10. Soil Hydraulic Conductivity (SOL_K): Calibrate to soil type to accurately model infiltration and percolation.
  11. Water Table Depth (WTABLE): Adjust to match observed data, considering geological variability.

Methodological Approach:

  • Sensitivity Analysis: Use Latin Hypercube or SUFI-2 to identify sensitive parameters.
  • Uncertainty Analysis: Apply GLUE or ParaSol to assess model reliability and parameter uncertainty.
  • Data Requirements: Ensure access to groundwater levels, recharge rates, and streamflow data for calibration and validation.
  • Model Validation: Split data for calibration and validation to ensure robust performance.
  • Regional Calibration: Consider parameter transfer or regionalization from similar watersheds.
  • Agricultural Practices: Integrate effects of practices like irrigation and tillage into parameter adjustments.

By focusing on these parameters and employing sensitivity, uncertainty, and validation analyses, the SWAT model can be effectively calibrated to simulate groundwater recharge accurately in the specified semi-arid, complex geological setting.