Interacting Vegetative and Thermal Contributions to Water Movement in Desert Soil

Abstract

Thermally driven water‐vapor flow can be an important component of total water movement in bare soil and in deep unsaturated zones, but this process is often neglected when considering the effects of soil–plant–atmosphere interactions on shallow water movement. The objectives of this study were to evaluate the coupled and separate effects of vegetative and thermal‐gradient contributions to soil water movement in desert environments. The evaluation was done by comparing a series of simulations with and without vegetation and thermal forcing during a 4.7‐yr period (May 2001–December 2005). For vegetated soil, evapotranspiration alone reduced root‐zone (upper 1 m) moisture to a minimum value (25 mm) each year under both isothermal and nonisothermal conditions. Variations in the leaf area index altered the minimum storage values by up to 10 mm. For unvegetated isothermal and nonisothermal simulations, root‐zone water storage nearly doubled during the simulation period and created a persistent driving force for downward liquid fluxes below the root zone (total net flux ∼1 mm). Total soil water movement during the study period was dominated by thermally driven vapor fluxes. Thermally driven vapor flow and condensation supplemented moisture supplies to plant roots during the driest times of each year. The results show how nonisothermal flow is coupled with plant water uptake, potentially influencing ecohydrologic relations in desert environments.

Simulation of Water Use Dynamics by Salix Bush in a Semiarid Shallow Groundwater Area of the Chinese Erdos Plateau

“…In other words, the liquid water was dominant due to the large amount of transpiration, even though the rainfall decreased by half (Table 6). This phenomenon agrees with the results reported by Garcia, et al [15]. Although the amount of water vapor flux is small, the mean pressure over the root zone is very low during dry periods with heat flow (Figure 7).…”

“…Temperature-driven soil water flow is another process that can affect water balance and movement in arid and semi-arid areas [15]. The dynamics of liquid water and water vapor movement have been determined based on the mathematical description of liquid water and vapor flux by Philip and de Vries [16] for unsaturated soils under a soil water pressure head and a soil temperature gradient.…”

“…The dynamics of liquid water and water vapor movement have been determined based on the mathematical description of liquid water and vapor flux by Philip and de Vries [16] for unsaturated soils under a soil water pressure head and a soil temperature gradient. This study produced a mathematical model [1,17] based on the influence of air flow [18], meteorological conditions [19], and vegetation cover [15,20]. However, there have been limited modeling studies evaluating the role of coupled fluxes and their temporal variation in desert bush-dominated areas under shallow groundwater level conditions.…”

Modelling vegetation water-use and groundwater recharge as affected by climate variability in an arid-zone Acacia savanna woodland

“…(2) Groundwater is a valuable natural resource, which not only supports human activities, but also 39 has a key role in sustaining the health of wide-spread groundwater dependent ecosystems ( water availability, which in turn, result in a number of complex hydrologic processes (Gee et al, 1994;45 Porporato et al, 2002;Scanlon et al, 2005;Garcia et al, 2011). Climate variations, which lead to 46 changes in vegetation structure and/or its water-use, can have a follow-on impact on recharge to 47 groundwater under vegetation.…”

“…Sustainable water resource management is a major challenge for water 41 resource managers in arid and semi-arid regions (Fernandez et al, 2002), where excessive and 42 unsympathetic groundwater abstraction can degrade vegetation health (Clifton and Evans, 2001, 43 Donohue et al, 2007). Vegetation dynamics in arid and semi-arid regions largely depend on soil 44 water availability, which in turn, result in a number of complex hydrologic processes (Gee et al, 1994; 45 Porporato et al, 2002; Scanlon et al, 2005;Garcia et al, 2011). Climate variations, which lead to 46 changes in vegetation structure and/or its water-use, can have a follow-on impact on recharge to 47 groundwater under vegetation.…”