<abstract xmlns="http://www.w3.org/1999/xhtml"><p>Longwave radiation, as part of the radiation balance, is one of the factors needed to estimate potential evapotranspiration (PET). Since the longwave radiation balance is rarely measured, many computational methods have been designed. In this study, we report on the difference between the observed longwave radiation balance and modelling results obtained using the two main procedures outlined in FAO24 (relying on the measured sunshine duration) and FAO56 (based on the measured solar radiation) manuals. The performance of these equations was evaluated in the April–October period over eight years at the Liz experimental catchment and grass surface in the Bohemian Forest (Czech Republic). The coefficients of both methods, which describe the influence of cloudiness factor and atmospheric emissivity of the air, were calibrated. The Penman-Monteith method was used to calculate the PET. The use of default coefficient values gave errors of 40–100 mm (FAO56) and 0–20 mm (FAO24) for the seasonal PET estimates (the PET was usually overestimated). Parameter calibration decreased the FAO56 error to less than 20 mm per season (FAO24 remained unaffected by the calibration). The FAO56 approach with calibrated coefficients proved to be more suitable for estimation of the longwave radiation balance.</p></abstract>

Longwave radiation, as part of the radiation balance, is one of the factors needed to estimate potential evapotranspiration (PET). Since the longwave radiation balance is rarely measured, many computational methods have been designed. In this study, we report on the difference between the observed longwave radiation balance and modelling results obtained using the two main procedures outlined in FAO24 (relying on the measured sunshine duration) and FAO56 (based on the measured solar radiation) manuals. The performance of these equations was evaluated in the April–October period over eight years at the Liz experimental catchment and grass surface in the Bohemian Forest (Czech Republic). The coefficients of both methods, which describe the influence of cloudiness factor and atmospheric emissivity of the air, were calibrated. The Penman-Monteith method was used to calculate the PET. The use of default coefficient values gave errors of 40–100 mm (FAO56) and 0–20 mm (FAO24) for the seasonal PET estimates (the PET was usually overestimated). Parameter calibration decreased the FAO56 error to less than 20 mm per season (FAO24 remained unaffected by the calibration). The FAO56 approach with calibrated coefficients proved to be more suitable for estimation of the longwave radiation balance.

The influence of observed and modelled net longwave radiation on the rate of estimated potential evapotranspiration

The Institute of Hydrodynamics of the Czech Academy of Sciences

Department of Physical Geography and Geoecology, Faculty of Science

Journal of Hydrology and Hydromechanics

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Longwave radiation, as part of the radiation balance, is one of the factors needed to estimate potential evapotranspiration (PET). Since the longwave radiation...

The influence of observed and modelled net longwave radiation on the rate of estimated potential evapotranspiration

Published Online: Jun 26, 2019

Page range: 280 - 288

Received: Sep 11, 2018

Accepted: Jan 18, 2019

DOI: https://doi.org/10.2478/johh-2019-0011

Keywords
Radiation balance, Longwave radiation, Potential evapotranspiration, Penman-Monteith, Calibration

© 2019 Jitka Kofroňová et al., published by Sciendo

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

The influence of observed and modelled net longwave radiation on the rate of estimated potential evapotranspiration

Published Online: Jun 26, 2019

Page range: 280 - 288

Received: Sep 11, 2018

Accepted: Jan 18, 2019

DOI: https://doi.org/10.2478/johh-2019-0011

KeywordsRadiation balance, Longwave radiation, Potential evapotranspiration, Penman-Monteith, Calibration

© 2019 Jitka Kofroňová et al., published by Sciendo

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Keywords
Radiation balance, Longwave radiation, Potential evapotranspiration, Penman-Monteith, Calibration