A national-scale Taguchi-based experimental design for optimizing watershed health and ecological security under high-dimensional complexity

Abstract

Assessing watershed health (WH) and ecological security (ES) is a fundamental pillar of environmental sustainability,
yet achieving these goals is increasingly hindered by the complexity of the systems involved. Watersheds
are governed by a complex web of interconnected variables, from soil and geological constraints to
fluctuating climate patterns and diverse human interventions, that collectively influence WH and ES. This study
adapted the WH and ES maps from a previous national PSR-based assessment. In contrast, the novelty of the
present work lies in quantifying the effect sizes of the controlling factors using the Taguchi optimization method.
As a result, it is critical to identify the most influential decision variables and measure their effect sizes to ensure
management efforts focus on high-impact interventions. To address this complexity, this study employs the
Taguchi Method, a sophisticated fractional factorial experimental design. Unlike traditional “one-factor-at-atime”
approaches, the Taguchi framework is well suited to optimizing WH and ES because it uses orthogonal
arrays to examine multiple decision variables with fewer experiments. By analyzing the signal-to-noise (S/N)
ratio, this method helps identify the “ideal configuration” of decision variables that remains effective even with
uncontrollable environmental noise. Applying this method to 3rd-order watersheds reveals a clear hierarchy of
influence, showing that human management factors, rather than natural constraints, are the main levers for WH
and ES. The analysis identified the Minimum Normalized Difference Tillage Index as the most critical criterion,
accounting for 18.47% and 29.32% of the variance in WH and ES, respectively. This indicates that optimizing
agricultural soil management yields the highest ecological return. Additionally, the study identifies the Area of
Unimplemented Biological Watershed Operations as a secondary yet important stressor, highlighting a significant
gap in current conservation efforts. While geological factors such as Fault Length and climate variability set
baseline boundary conditions, they are statistically subordinate to these controllable human pressures. Ultimately,
this research offers an evidence-based optimization framework, demonstrating that optimized ecosystem
services require improved tillage and biological restoration within integrated policies