Reconciling the isotope-based fog classification with meteorological conditions of different fog types

Abstract

Although fog is an important component of the hydrological cycle of drylands, its formation mechanisms are not fully understood leading to discrepancy of fog type classifications using different methodologies. Such discrepancies may result in under or over estimation of the potential impacts of global climate change on the ecohydrology of fog dependent ecosystems. To fill this knowledge gap, this study applies hydrogen and oxygen stable isotopes to objectively classify fog and compares this classification to meteorological conditions defined for the formation of these fog types. Results suggest that this isotope based fog classification method is consistent with expected meteorological conditions for the different fog types such as radiation fog, advection fog and mixed fog. Wind speeds decreased from advection, to radiation fog while estimated fog (cloud) height was lowest during radiation fog and highest during advection fog. In addition, precipitation-offset (lc-excess) suggests that radiation and advection fog had different moisture sources, with radiation fog being locally sourced and advection fog originating from the ocean. This study suggests isotope-based fog classification is an objective method that could be applied to other coastal fog dependent ecosystems to help assess the potential impact of climate change on these ecosystems.