HR: 1340h
AN: H33B-1260    [Abstracts]
TI: A rational function approach for estimating land surface evapotranspiration based on the complementary hypothesis
AU: Han, S
EM: hans99@mails.tsinghua.edu.cn
AF: Tsinghua University, Department of Hydraulic Engineering, Tsinghua University, Beijing, 100084, China
AU: Hu, H
EM: huhp@tsinghua.edu.cn
AF: Tsinghua University, Department of Hydraulic Engineering, Tsinghua University, Beijing, 100084, China
AU: * Tian, F
EM: tianfq@uiuc.edu
AF: Tsinghua University, Department of Hydraulic Engineering, Tsinghua University, Beijing, 100084, China
AB: Evapotranspiration, which occurs in the boundary layer between the land surface and the bottom atmospheric layer, plays an important role in both water balance and energy balance. Models based on the Penman hypothesis (1948) and the Budyko hypothesis (1974) estimate actual evapotranspiration from a land surface process prospective, while models based on the complementary hypothesis (Bouchet, 1963) do this from the atmospheric perspective. Penman-based models require detailed data on soil moisture or stomatal resistance (Crago and Crowley, 2006); Budyko models, e.g. Fu's equation (1981), estimate the mean annual evapotranspiration only; while models based on the complementary hypothesis, including advection aridity model (AA for short) (Brutsaert and Stricker, 1979) and the Granger model (1989, 1991, 1996) estimate actual evapotranspiration at various time scales using climate data only. The AA and Granger models use different definitions for wet environment evaporation and potential evaporation and their comparative study are conducted by several researchers (Xu and Singh, 2005; Liu et al., 2006; Crago and Crowley, 2006). In this paper we explore the uniformity of the two complementary models by dimensional analysis. A new index (the proportion of the radiation term in Penman equation, termed the air humidity index) is proposed as a measure of the wetness of the evaporating surface via the wetness of over-passing air, and a general functional form for actual evaporation is developed in which the evaporation ratio is expressed as a function of the air humidity index. The similarity and differences between the AA and Granger models are interpreted via this rational function approach, and a new power function method is proposed. The theoretical analysis is confirmed by observational data under various climate conditions.
DE: 1814 Energy budgets
DE: 1818 Evapotranspiration
SC: Hydrology [H]
MN: 2007 Fall Meeting