The contribution of fog to the water balance of Mediterranean climate-type coastal forests

In Mediterranean climate-type coastal ecosystems, where precipitation rates are lower than evapotranspiration, fog contributes to the ecosystem’s water balance. Although the interception of fog water by vegetation is well-documented, its contribution to the overall water balance remains unclear. In this study we aim to understand the role of fog water as an input to the water balance in a representative Mediterranean climate-type coastal forest in Chile. By combining the water balance approach with a fog harvesting model , we characterize the key components of water storage, precipitation, fog, and evapotranspiration across different slopes of a coastal forest. Main results indicate that forest fog collection efficiency should average ~45% to maintain the forest water balance. However, in-situ measurements of fog dripping show a collection efficiency of ~12%, suggesting that more complex mechanisms, such as foliar water absorption, may also contribute to the total forest fog collection efficiency. Moreover, we demonstrate that fog acts as a consistent water input in these forests, contributing ~18% to their monthly water balance complementing precipitation by an additional 20% to 40%, depending on slope orientation (~120 mm y -1 ). This research provides evidence to clarify the role of fog in supporting the resilience of Mediterranean climate-type forests, which are highly threatened by climate change, land cover conversion, urban sprawl and fires.