What factor has the greatest influence on ET in desert ecosystems?

Vapor Pressure Deficit (VPD) is a crucial factor in influencing evapotranspiration (ET) in desert ecosystems. VPD represents the difference between the amount of moisture the air can hold when it is saturated and the actual amount of moisture in the air. In dry environments such as deserts, the air typically has a low moisture content, leading to a high VPD.

High VPD conditions drive higher rates of water loss through transpiration from plant surfaces and evaporation from soil because the dry air increases the gradient that moisture travels from the surface to the atmosphere. Essentially, the higher the VPD, the more water is needed to saturate the air, thus accelerating the process of ET. In desert ecosystems, where water availability is already limited, a high VPD can significantly influence plant water stress, growth, and overall ecosystem health.

While temperature, soil salinity, and humidity all affect ET, they do so to lesser extents compared to VPD in the context of these ecosystems. Temperature influences the rate of transpiration but does not solely dictate how much water is lost; soil salinity can impact plant health and thus indirectly influence ET; and humidity affects both VPD and ET but does not serve as a direct driver in the