Vol.7, No 2, 2009 pp. 171 - 178
UDC 626.81/.84:551.573:556.132(045)
DOI: 10.2298/FUACE0902171T
EFFECT OF ACTUAL VAPOR PRESSURE ON ESTIMATING EVAPOTRANSPIRATION AT SERBIA
Slaviša Trajković1, Svetlana Živković2
1Faculty of Civil Engineering and Architecture, University of Niš
2PWRC Srbijavode, WRC Morava, Niš, Serbia
E-mail: slavisa@gaf.ni.ac.rs
Actual vapor pressure (VP) is an important parameter that is used in many evapotranspiration equations. However, vapor pressure is difficult to measure accurately. In the humid climate, the actual vapor pressure can be derived from minimum air temperature. The objectives of this study were: first, to estimate errors that can arise if VP data are not available and have to be estimated; second, to compare the Priestley-Taylor ET0 values computed under various levels of VP data availability; and third, to evaluate the reliability of Priestley-Taylor equation as compared to the FAO-56 Penman-Monteith method. The following main conclusions can be drawn: Estimated VP values generally were in closest agreement with measured VP values. The measurements of air humidity at humid locations are not indispensable for estimating reference evapotranspiration. The Priestley-Taylor method (with measured or estimated VP) provides the very good agreement with the evapotranspiration obtained by the FAO-56 Penman-Monteith method except windless locations.
Key words: Vapor pressure, Reference evapotranspiration, FAO-56 Penman-Monteith, Priestley-Taylor
UTICAJ STVARNOG PRITISKA VODENE PARE NA PRORAČUN EVAPOTRANSPIRACIJE U SRBIJI
Vlažnost vazduha jedan je od najvažnijih klimatskih faktora koji odredjuju proces evapotranspiracije. Stvarni napon vodene pare se izražava preko temperature tačke rose. U humidnoj klimi se ova vrednost može zameniti minimalnom dnevnom temperaturom. Ciljevi ovog rada su bili da se procene odstupanja koja se mogu desiti ako ne koristimo merene vrednosti stvarnog napona vodene pare (VP), da se uporede Priestley-Taylor (PT) ET0 vrednosti dobijene sa i bez merenih VP vrednosti i da se proceni pouzdanost PT metode u poredjenju sa standardnom FAO-56 PM metodom. Sledeći glavni zaključci se mogu izvesti iz ovog istraživanja: Sračunate VP vrednosti su, generalno, veoma bliske merenim VP vrednostima. Merenja relativne vlažnosti nisu neophodna za proračun referentne evapotranspiracije u humidnoj klimi Srbije. PT metoda obezbedjuje veoma dobro slaganje sa FAO-56 PM metodom izuzev lokacija sa malom brzinom vetra.
Ključne reči: Pritisak vodene pare, Referentna evapotranspiracija, FAO-56 Penman-Monteith, Priestley-Taylor