Net Radiation Estimations in Evapotranspiration Research over Different Canopy Surfaces in a Humid Climate

Accurate determination of potential and reference evapotranspiration is essential to estimate water balances. In most standardized methods, such as the Penman-Monteith and Priestley-Taylor methods, net radiation is one of the most important forcing data. Unfortunately few stations measure net radiation. Instead, net radiation is typically calculated from solar radiation, ancillary climate variables, and albedo values derived from the literature. This research evaluates a series of methods used to calculate net radiation over different canopy surfaces. The four components of net radiation were measured at eight locations including urban, agricultural, rangeland, forest, wetland, and open water land types in central Florida. Data collected from January 2004 to December 2005 were used in this analysis. The results identify the most appropriate method to estimate net radiation and quantify net radiation and potential ET error estimates by method. Additionally, the impact of diurnal and seasonal albedo changes on net radiation calculations is examined.