A Water Balance Approach to Estimate Fog Water Contribution to a Relict Forest in the Coastal Semi-Arid Region in Central Chile
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Date
2024
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Abstract
The marine fog presence along Chile’s western coast, in the semi-arid and Mediterranean region, influences coastal vegetation patterns and constitutes a significant yet underestimated water source for basin water balance. While studies suggest that south-westerly winds transport marine fog inland, serving as a vital water source for coastal vegetation and relict forests, our understanding of fog dynamics in this context remains limited. Therefore, the aim of this study is to analyze coastal fog in the coast of the semi-arid and mediterranean region in central Chile addressing the temporal distribution of its frequency, liquid water content and water collection in relation to the presence of relict forests. This study is centered in a relict forest located in the semi-arid coastal Chile uphill 3.5 km far from the coast with an altitude of 650 meters (lat: -32.2°/long: -71.5°). This forest, dominated by Aextoxicon punctatum survives on less than 200 mm of annual precipitation which implies fog water is a critical water input. Our methodological approach is a water balance analysis tailored for fog-related water contributions, the balance considers precipitation, evapotranspiration (ET), soil accumulation, and fog input across various scales: from individual trees to the entire mountainous ecosystem. Specific methods for fog characterization, forest assessment, and fog capture efficiency are developed, incorporating factors such as forest characteristics and vertical variability. Our findings reveal that fog recurs 17% of the time and contributes up to 75% to the forest’s water evapotranspiration. Furthermore, it was estimated that forests can capture up to 10.5% of the available fog in the air. Considering soil moisture sensor data collected in the study area it appears that the captured fog does not penetrate deep into the soil and does not generate runoff from the forest area. Based on a sensitivity analysis we explored how forest’s fog capture efficiency varies with elevation, collection area (leaf area index), and evapotranspiration. These results underscore the importance of fog water as a vital water source for vegetation and emphasize the need for incorporating fog water inputs into broader assessments for improved water resource predictions and ecosystem conservation.
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Aextoxicon punctatum, Fog, Semi-arid, Relict forest, Standard fog collectors, Water balance