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|Title:||An auto-calibration procedure for empirical solar radiation models|
|Authors:||BOJANOWSKI Jedrzej; DONATELLI Marcello; SKIDMORE Andrew; Vrieling A.|
|Citation:||ENVIRONMENTAL MODELLING \& SOFTWARE vol. 49 p. 118-128|
|Publisher:||ELSEVIER SCI LTD|
|Type:||Articles in periodicals and books|
|Abstract:||Solar radiation is the main input for estimating evapotranspiration and the accumulation of plant biomass when simulating crop growth. Direct measurement of solar radiation is now carried out in most European countries, but the network of measuring stations is too sparse for the reliable interpolation of measured values. Instead of direct measurements, empirical solar radiation models may be used to estimate solar radiation from more commonly measured variables or from direct outputs of general circulation models (such as air temperature). Coefficients for these models are site-dependent. This usually implies that they are estimated for stations with direct radiation measurements, but need to be interpolated for other locations. In this paper, we introduce a procedure to auto-calibrate empirical solar radiation models that are based on daily temperature range (Hargreaves, and Bristow and Campbell). We demonstrate that daily solar radiation can be accurately estimated from daily air temperature range measurements without site-specific empirical coefficients that require stations that measure solar radiation. The average relative root mean square error for our auto-calibrated models was 0.74 % higher for the Bristow and Campbell model (p<0.05, n=126), and 2.25 % higher for the Hargreaves model (p<0.05, n=126) in comparison to the ground-measurements-based calibration. For the Bristow and Campbell model, the decrease in model performance was not statistically significant for two out of the four performance statistics tested in this study. When our new solar radiation retrieval algorithm is used to estimate evapotranspiration, we found similar accuracies between solar radiation input from ground- and auto-calibration. We conclude that our auto-calibration procedure results in accurate solar radiation retrievals, and it requires only air temperature as input. Time series of temperature are available for many weather stations, or alternatively are estimated by general circulation models. The same procedure could easily be applied to other empirical solar radiation models.|
|JRC Directorate:||Sustainable Resources|
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