Important factors to model climate change effects on evapotranspiration

Although growers have considerable control over crop production, a major concern is the anticipated
increase in evapotranspiration (ET) due to global warming. ET rates, however, are also affected by
radiation, humidity, wind speed, crop morphology, and crop physiology in addition to temperature.
Crop ET (ETc) is commonly estimated as the product of reference ET (ET0) and a crop coefficient (Kc),
and the main factors affecting Kcvalues are net radiation, aerodynamic resistance, and canopy
resistance differences between the reference and crop surfaces. The standardized ET0equation has
fixed values for the canopy resistance (rc), and different values are likely for other crops. The rcvalues
might also adjust with increasing CO2and higher temperature. Aerodynamic resistance (ra) depends on
atmospheric stability, wind speed, and surface roughness. The relative aerodynamic contributions of
sensible heat to ET0and ETccould change if the canopy development or the wind speed climatology
are modified by global warming. In this paper, we will discuss how the ET0and Kcvalues vary with
microclimate and how Kcvalues and ET0rates might react to global warming.