Abstract Fog is considered as an important source of water in many drylands, and the knowledge of possible sources of its formation is essential to make future predictions. Prior studies have suggested the presence of locally generated fog in drylands; however, its formation mechanism remains unclear. There have been studies on the effects of fog on soil moisture dynamics. On the contrary, no research has yet been conducted to understand the potential contribution of soil moisture to fog formation. This study, therefore, for the first time intends to examine such possibility in a fog-dominated dryland ecosystem, the Namib Desert. The study was conducted at two sites representing two different land forms (sand dunes and gravel plains) in the Namib Desert. We first examined evidence of fog formation through water vapor movement using field observations, and then simulated water vapor transport using HYDRUS-1D model. In the first part of the study, soil moisture, soil temperature and air temperature data were analyzed, and the relationships between these variables were taken as one of the key indicators for the linkage between soil water and fog formation. The analysis showed that increase in soil moisture generally corresponded to similar increase in air or soil temperature near the soil surface, which implied that variation in soil moisture might be the result of water vapor movement (evaporated soil moisture) from lower depths to the soil surface. In the second part of the study, surface fluxes of water vapor were simulated using the HYDRUS-1D model to explore whether the available surface flux was sufficient to support fog formation. The surface flux and cumulative evaporation obtained from the model showed positive surface fluxes of water vapor. Based on the field observations and the HYDRUS-1D model results, it can be concluded that water vapor from soil layers is transported through the vadose zone to the surface and this water vapor likely contributes to the fog formation in fog-dominated drylands, like the Namib Desert.

中文翻译：

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土壤水分对纳米布沙漠雾形成的潜在贡献

摘要 雾被认为是许多旱地的重要水源，了解雾形成的可能来源对于未来的预测至关重要。先前的研究表明，旱地存在局部产生的雾；但其形成机制尚不清楚。已有关于雾对土壤水分动态影响的研究。相反，尚未进行任何研究来了解土壤水分对雾形成的潜在贡献。因此，这项研究首次打算在以雾为主的旱地生态系统纳米布沙漠中检验这种可能性。该研究在代表纳米布沙漠两种不同土地形态（沙丘和砾石平原）的两个地点进行。我们首先使用实地观察检查了通过水汽运动形成雾的证据，然后使用 HYDRUS-1D 模型模拟了水汽输送。研究的第一部分对土壤水分、土壤温度和气温数据进行了分析，并将这些变量之间的关系作为土壤水分与雾形成联系的关键指标之一。分析表明，土壤水分的增加通常对应于土壤表面附近空气或土壤温度的类似升高，这意味着土壤水分的变化可能是水汽从较低深度向土壤表面移动（蒸发的土壤水分）的结果。 . 在研究的第二部分，使用 HYDRUS-1D 模型模拟了水蒸气的表面通量，以探索可用的表面通量是否足以支持雾的形成。从模型获得的表面通量和累积蒸发量显示出正的水汽表面通量。根据现场观测和 HYDRUS-1D 模型结果，可以得出结论，来自土壤层的水汽通过包气带输送到地表，这种水汽可能有助于雾为主的旱地的雾形成，如纳米布沙漠。