Fuel Moisture Model Calibration under Natural Hazard Conditions : A Case Study in Andean Cypress-Coihue Mixed Forests, Northwestern Patagonia

Recent decades have seen a marked intensification of wildfire regimes worldwide, posing increasing risks to temperate forests. In northwestern Patagonia, Argentina, these changes threaten biodiversity-rich Andean foothill forests dominated by Austrocedruschilensis and Nothofagus dombeyi. Yet, most operational fuel moisture models, such as those embedded in the Canadian Forest Fire Danger Rating System, remain calibrated for Northern Hemisphere conditions and may not accurately reflect the microclimatic variability of Patagonian mountain forests.

This study develops and validates a site-specific calibration of 10-hour fuel moisture models under natural hazard conditions in the El Manso Valley, Río Negro Province. Field-based gravimetric measurements were combined with automated reference-stick data to examine diurnal dynamics of fuel moisture content (FMC) across contrasting canopy types. Linear calibration models were established to quantify relationships between stand-level FMC, local relative humidity, and standardized reference-stick readings.

Results demonstrate pronounced species-specific differences: in the open Austrocedrus stand, FMC showed moderate correlation with relative humidity (R² = 0.330), indicating short- term atmospheric coupling. In contrast, Nothofagus fuels exhibited almost invariant moisture conditions (R² ≈ 0.003) due to canopy buffering and reduced air exchange. Standard models such as the Fine Fuel Moisture Code (FFMC) and reference-stick calibrations consistently overpredicted drying rates under shaded and mesic conditions.

These findings highlight the need for regionally adapted calibration schemes that incorporate canopy structure and microclimatic controls. The study provides an empirical basis for improving the accuracy of fire danger rating systems in southern temperate forests and contributes to a broader understanding of fuel–climate interactions under increasing wildfire risk.