Contribution of surface evaporation to winter fog formation: Numerical simulation of water transport in silty soils of SW Hungary using the Hydrus-1D model

Baranya, SW Hungary The impact of soil moisture on fog formation is studied using the Hydrus-1D numerical model. Four different fog events were chosen to simulate the time evolution of the water content profiles and evaporation from the surface. The observed soil temperature and water content were used to provide the initial condition for the numerical model, and to validate the model results. A sensitivity study was performed to reveal the impact of uncertainties. The results can be summarized as follows: (i) uncertainty on the initial soil moisture content do not influence the surface vapor flux significantly; (ii) discrepancy between the observed and simulated soil moisture profile may have a small effect on the reliability of the simulated surface evaporation; (iii) surface evaporation is governed by both the relative humidity in the atmosphere and the soil moisture in the uppermost 10 cm layer. If the relative humidity is larger the 90 % the surface evaporation is ceased; (iv) surface evaporation continuously enhances the specific humidity in the atmosphere, shortening the time period required for the cooling the atmosphere become saturated for the fog formation; (v) in the investigated cases the fog forms after the cessation of surface evaporation, and the rate of evaporation is negligible if the atmospheric relative humidity is higher than 90 % during fog events. • The Hydrus −1D model simulates the temporal evolution of soil moisture prior to and during fog events well. • Evaporation is mostly impacted by the moisture content in the top 10-cm layer of soil and by relative humidity. • The estimated impact of evaporation on the vapor content is qualitatively supported by the meteorological data.