Abstracts Geography

Nighttime evapotranspiration in a semiarid climate using a hemispherical chamber

by Jacob Collison

Nighttime evapotranspiration (ETn) is typically underestimated, miscalculated or ignored when producing daily, seasonal, or annual evapotranspiration (ET) models using energy-balance and aerodynamic conceptual models, such as the Penman-Monteith ET equation. The objective of this study is to increase the understanding of ETn contribution to daily ET (ET24) sums by using a hemispherical chamber to measure ETn on three separate nights in the spring, summer, and fall in eastern Bernalillo County, New Mexico, 2012; a semiarid region where annual potential ET losses exceed annual precipitation. The hemispherical chamber is equipped with high-accuracy relative humidity and temperature sensors that measure ET directly using the methods described in Stannard (1988). The hemispherical chamber measurements were used to calibrate a Penman-Monteith (PM) equation to better account for ETn by incorporating separate stomatal conductance models for daytime and nighttime. The amount of ETn measured on these three nights were estimated to be 25 percent of the total ET24 modeled from micrometeorological data. Results from this study suggest that the single stomatal conductance PM model underestimated daily ET, due to inaccurately modeling ETn, which is equivalent to 132 mm over a growing season in a semiarid climate.