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

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 l...

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Bibliographic Details
Published in:Journal of Hydrology and Hydromechanics 2019-09, Vol.67 (3), p.280-288
Main Authors: Kofroňová, Jitka, Tesař, Miroslav, Šípek, Václav
Format: Article
Language:English
Subjects:
Atmosphere
Atmospheric models
Calibration
Catchment area
Cloud cover
Cloudiness
Coefficients
Computer applications
Duration
Emissivity
Energy
Evapotranspiration
Evapotranspiration estimates
Humidity
Hydrologic cycle
Hydrology
Long wave radiation
longwave radiation
Mathematical models
Measurement methods
penman-monteith
Potential evapotranspiration
Precipitation
Procedures
Radiation
Radiation balance
Radiation measurement
Solar radiation
Sunshine duration
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Summary: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.
ISSN:0042-790X
1338-4333
0042-790X
DOI:10.2478/johh-2019-0011