SWAT+ Single and Multi-Site Calibration in a Semi-Arid Watershed
Mohamed Yacoubi
ABSTRACT
Calibration is a critical step in watershed modeling. The availability of more data generally leads to more accurate calibration, making multisite calibration valuable when multiple hydrologic gauging stations are present. In this study, we compare the performance of the SWAT+ model, applied to a watershed in southern Morocco equipped with three gauging stations, by evaluating different calibration strategies provided by the latest version of the SWAT+ Toolbox (v3.0.6). These strategies include single-site calibration (individual calibration at the outlet station), multisite one-step calibration (calibrating all sub-basins simultaneously), and multisite multi-step calibration (calibrating sub-basins sequentially). The analysis aims to improve calibration strategies for watershed modeling under semiarid climates, where water resource management is particularly sensitive to calibration uncertainties due to data scarcity. It demonstrates that multi-site multi-step calibration significantly improves the spatial representation of hydrological processes compared to single-site calibration, although predictive uncertainty remains high during validation for some sub-basins.
