Important factors to model climate change effects on evapotranspiration

Abstract

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 (ETo) and a crop coefficient (Kc), and the main factors affecting Kc values are net radiation, aerodynamic resistance, and canopy resistance differences between the reference and crop surfaces. The standardized ETo equation has fixed values for the canopy resistance (rc), and different values are likely for other crops. The rc values might also adjust with increasing CO2 and higher temperature. Aerodynamic resistance (ra) depends on atmospheric stability, wind speed, and surface roughness. The relative aerodynamic contributions of sensible heat to ETo and ETc could change if the canopy development or the wind speed climatology are modified by global warming. In this paper, we will discuss how the ETo and Kc values vary with microclimate and how Kc values and ETo rates might react to global warming. © 2008, Page Press Publications. All rights reserved.