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Evapotranspiration Remote Sensing and Modeling Part 2

Tham khảo tài liệu 'evapotranspiration remote sensing and modeling part 2', khoa học tự nhiên, công nghệ sinh học phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 2 Evapotranspiration Estimation Based on the Complementary Relationships Virginia Venturini1 Carlos Krepper1 2 and Leticia Rodriguez1 1Centro de Estudios Hidro-Ambientales-Facultad de Ingeniería y Ciencias Hídricas Universidad Nacional del Litoral 2Consejo Nacional de Investigaciones Científicas y Técnicas Argentina 1. Introduction Many hydrologic modeling and agricultural management applications require accurate estimates of the actual evapotranspiration ET the relative evaporation F and the evaporative fraction EF . In this chapter we define ET as the actual amount of water that is removed from a surface due to the processes of evaporation-transpiration whilst the potential evapotranspiration Epot is any other evaporation concept. There are as many potential concepts as developed mathematical formulations. In this chapter F represents the ratio between ET and Epot as it was introduced by Granger Gray 1989 . Meanwhile EF is the ratio of latent flux over available energy. It is worthy to note that in general the available evapotranspiration concepts and models involve three sets of variables i.e. available net radiation Rn atmospheric water vapor content or temperature and the surface humidity. Hence different Epot formulations were derived with one or two of those sets of variables. For instance Penman 1948 established an equation by using the Rn and the air water vapor pressure. Priestley Taylor 1972 derived their formulations with only the available Rn. In the last three decades several models have been developed to estimate ET for a wide range of spatial and temporal scales provided by remote sensing data. The methods could be categorized as proposed by Courault et al. 2005 . Empirical and semi-empirical methods These methods use site specific or semi-empirical relationships between two o more variables. The models proposed by Priestley Taylor 1972 hereafter referred to as P-T Jackson et al. 1977 Seguin et al. 1989 Granger Gray 1989 Holwill Stewart 1992 Carlson