Building trust in large-scale water quality models: 13 alternative strategies beyond validation

Validating large-scale water quality models is challenging because of the variety of water quality constituents, and scales for which observations are limited. Here, in this perspective, we propose 13 alternative strategies to build trust in large-scale water quality models beyond validation and discuss their strengths and weaknesses regarding their validity, reliability, and applicability. Our alternative strategies aim to evaluate separately model inputs (Strategies 1–4), outputs (Strategies 5–6) and structures (Strategy 7) as well as these aspects together (Strategies 8–13). This is done via methods such as comparisons (Strategies 1–3, 6–8, 12–13), sensitivity analysis (Strategy 5), use of innovations (Strategy 9), expert knowledge (Strategy 11) and local models (Strategy 13). The proposed strategies vary in their validity, reliability, and applicability. Validation is an important starting point but should be used in combination with other strategies. Our proposed list opens the discussion to improve methods to evaluate global water quality models.