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.