Regional Calibration of Solar Radiation and Reference Evapotranspiration Estimates with Minimal Data in Florida

Abstract

Reference evapotranspiration and solar radiation estimation methods that use only measured temperature have been demonstrated to require regional calibration for acceptable performance. This study was conducted to evaluate regional calibration of incoming solar radiation and reference evapotranspiration in Florida, USA. Using satellite-derived estimates of solar radiation and reference evapotranspiration as the standard for comparison, regional calibration of the Hargreaves-Samani solar radiation model and the Turc temperature-based reference evapotranspiration equation were evaluated using monthly temperature data from 22 weather stations in Florida. Station-specific and regional calibration of the Hargreaves-Samani solar radiation model was found to produce comparable results, indicating the validity of this approach in regional calibration of radiation estimates. Using the regionally calibrated radiation estimates, the original Turc equation was found to underestimate reference evapotranspiration, indicating an overall negative bias for the equation in the region. Using the regionally calibrated radiation estimates with the calibrated Turc equation was found to produce comparable error but considerably lower bias compared to the original Turc equation and the original Hargreaves-Samani solar radiation model using coefficients recommended by the Food and Agricultural Organization.