Abstract
In most land-surface models, the evolution of soil moisture is governed by soil-hydraulic processes. In hyper-arid soils, these processes break down, but soil moisture continues to show clear temporal variations, suggesting that other processes may be at work. We hypothesize that moisture in such soils varies due to evaporation in the soil and to vapour fluxes at the air–soil interface. To test this, we include vapour exchange between the air and soil in a land-surface model, apply the model to a desert site, and compare the simulated and observed soil moisture. The good agreement between the simulations and observations confirms our hypothesis. Using the model results, we examine the interactions between the soil-moisture and soil-vapour phases and influences of the soil-vapour phase on the surface energy balance.
Highlights
Modelling soil moisture in arid regions is important because, in addition to its possible impact on the surface energy balance, desert microbiological and morphological processes may sensitively depend on soil moisture
In land-surface models (LSMs), the evolution of soil moisture is considered to be governed by soil-hydraulic processes
We examine the interactions between the soil-moisture and soil-vapour phases, and the influences of the soil-vapour phase on the surface energy balance
Summary
Modelling soil moisture in arid regions is important because, in addition to its possible impact on the surface energy balance, desert microbiological and morphological processes may sensitively depend on soil moisture. For aeolian-sand and dust-transport studies, the threshold friction velocity needs to be estimated, which depends critically on soil moisture (McKenna Neuman and Sanderson 2008). Improving the representation of soil moisture for arid regions in global climate models is important to better understand the physical processes underlying the long-term climate memory (Blender and Fraedrich 2006; Wang et al 2010; Li and Wang 2020). Soil moisture θ in hyper-arid regions is generally very low. In land-surface models (LSMs), the evolution of soil moisture is considered to be governed by soil-hydraulic processes. For the Brooks and Corey (1964) soil-hydraulic parameters, θ r
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