2022 Volume 32 Issue 3 Pages 100
Recently, global warming has become one of the most alarming environmental issues around the world. Scientists have been warning that one of the primary effects of climate change is the disruption of the natural water cycle and the augmentation in the likelihood of more intense droughts and precipitation events. As mentioned by the United Nations Convention to Combat Desertification in 2017, deserts and drylands form about 40% of the total earth’s land, with approximately 12 million hectares being lost every year. The soil-atmosphere fluxes including evaporation and infiltration are complex processes that follow ambiguous mechanisms. In general, these processes are mainly controlled by the demand and supply, the ability of the porous medium to transmit water, and the vegetation. It must be noted that in arid and semi-arid regions the evaporation rate is extremely high and greatly exceeds the precipitation rate. Evaporation is a multiphase boundary complex phenomenon in which water gets lost from soil pores into the adjacent atmosphere. A typical actual evaporation curve can be divided into three stages, the constant rate stage, where capillary flow is dominant. Followed by the falling rate stage, which involves vapor diffusion transport through the top dry layer supported by capillary flow from the bottom. Finally, the residual stage, where vapor diffusion becomes dominant. A simple and environmental-friendly method that limits and controls the actual evaporation rate in arid and semi-arid regions is in great need to efficiently combat desertification.
Through this paper, a soil cover system that functions in a way to reduce the actual evaporation rate and maximizes the water conservation capabilities is proposed. The influence of the soil cover properties on the actual evaporation and water redistribution is investigated using 1-D column evaporation testes. Furthermore, considering the inevitable complexity associated with the governing flow mechanisms especially during the falling rate stage, an equivalent and robust micro-scale index that considers the variations in the pore-size distribution of each layer is approached to adequately elaborate the evaporation stages. It was found that the cover layer properties strongly affect the evaporation rate and the water storage capabilities through the bottom layer. Besides, focusing on a single macro-scale index to evaluate the evaporation flux and the dynamics of water movement might not be efficient. Instead, a comprehensive and robust microscale index is required to accurately estimate the actual evaporation behavior.
