Water Stress Explains the Aerodynamic versus Radiometric Surface
Temperature Paradox in Thermal-based Evaporation Modeling
Abstract
To explain the inequality between aerodynamic and radiometric surface
temperature, we used an analytical surface energy balance model where
evaporation is directly estimated by constraining the state equations of
aerodynamic temperature and biophysical conductances through radiometric
temperature. While the derived aerodynamic temperature was comparable
with a flux-inverted counterpart, evaporation and sensible heat fluxes
also showed good correspondence with in-situ eddy covariance
observations over contrasting aridity in Australia. Results showed
aerodynamic temperature frequently exceeds the radiometric temperature
in arid and semiarid ecosystems for two reasons: (i) declining
canopy-surface conductance and evaporative fraction due to escalated
water stress and vapor pressure deficit, and (ii) a simultaneous
increase in aerodynamic conductance, air temperature and sensible heat
flux. The analytical approach provides valuable insights into the
long-lasting debate of aerodynamic versus radiometric temperature
paradox by recognizing the feedback between biophysical conductances and
the supply-demand limit of solar radiation, soil moisture, and vapor
pressure deficit.