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Overview

Overview of SWATtunR Package

Source: vignettes/intro.Rmd
intro.Rmd

Introduction to SWATtunR

SWATtunR is an open-source R package designed to automate and enhance the calibration and validation of SWAT+ (Soil and Water Assessment Tool) models. It provides a flexible and comprehensive suite of functions and workflows to support users in building fully scripted, reproducible hydrological modeling processes in R.

The package integrates with other SWAT-related R packages as SWATbuildR, SWATprepR, SWATfarmR, SWATdoctR, SWATrunR, SWATmeasR, SWATreadR, and SWATdata — forming a powerful and interoperable ecosystem of tools for hydrological and environmental modelers working with SWAT/SWAT+ models.

Key functionalities of SWATtunR include:
  • Workflow initialization and setup
  • Parameter sampling strategies
  • Input and output data manipulation
  • Performance evaluation metrics
  • Advanced visualization of calibration and validation results
  • Model file management tools

To use SWATtunR, users must provide a working SWAT+ model setup along with the corresponding observed data. The package then guides in performing calibration and validation by adjusting parameters in three key SWAT+ input files Figure (ref?)(fig:fig1) :

  • plants.plt – crop yield (soft calibration)
  • hydrology.hyd – water yield ratio (soft calibration)
  • calibration.cal – model calibration parameters (hard calibration)

Calibration Workflow

The calibration process in SWATtunR is divided into two main stages: soft and hard calibration.

Soft calibration focuses on improving plant growth and water balance without altering core model dynamics. It involves:

  • Step 1: Calibrating crop growth parameters (days_mat, then optionally lai_pot, harv_idx, tmp_base, bm_e) to align simulated yields with observed statistics.
  • Step 2: Calibrating evapotranspiration components using esco and epco to match observed water yield ratios.

If crops fail to reach full maturity or the yield is unrealistic, crop management or the parameter ranges may need revision.

Hard calibration fine-tunes model parameters to observed discharge, sediment, and nutrient data. Two strategies are supported:

  • Sequential calibration: Stepwise adjustment of hydrological, sediment, and nutrient processes.
  • Simultaneous calibration: Joint tuning of all processes, improving fit for interrelated components like streamflow, nutrients, and sediments.

SWATtunR supports flexible workflows, including multi-site calibration, use of hydrological signatures, and multi-criteria performance evaluation to ensure robust model performance across varying conditions.