Abstract
An accurate estimation of terrestrial evapotranspiration over heterogeneous surfaces using satellite imagery and few meteorological observations remains a challenging task. Wind speed (u), which is known to exhibit high temporal-spatial variation, is a significant constraint in the abovementioned task. In this study, a wind speed-independent two-source energy balance (WiTSEB) model is proposed on the basis of a theoretical land surface temperature (Tr)-fractional vegetation coverage (fc) trapezoidal space and a two-stage evapotranspiration decomposing method. The temperatures in theoretically driest boundaries of the Tr-fc trapezoid are iteratively calculated without u by using an assumption of the absence of sensible heat exchange between water-saturated surface and atmosphere in the vertical direction under the given atmospheric condition. The WiTSEB was conducted in HiWATER-MUSOEXE-12 in the middle reaches of the Heihe watershed across eight landscapes by using ASTER images. Results indicate that WiTSEB provides reliable estimates in latent heat flux (LE), with root-mean-square-errors (RMSE) and coefficient of determination of 68.6 W m−2 and 0.88, respectively. The RMSE of the ratio of the vegetation transpiration component to LE is 5.7%. Sensitivity analysis indicates WiTSEB does not aggravate the sensitivity on meteorological and remote sensing inputs in comparison with other two-source models. The errors of estimated Tr and observed soil heat flux result in LE overestimation/underestimation over parts of landscapes. The two-stage evapotranspiration decomposing method is carefully verified by ground observation.
Highlights
Evapotranspiration (ET) plays a significant role in modeling the terrestrial hydrological cycle and energy exchange in a soil-vegetation-atmosphere system
Ere was averagely a little underestimation by 5.3 W m− 2 with an r2 of 0.82. e performance of estimated Rn varied with landscapes. at is, it was underestimated at corn, vegetable, and orchard landscapes, but was overestimated at desert steppe, Gobi, residential, and wetland sites. e largest error was occurring over the wetland landscape with an mean bias error (MBE) of 64.6 W m− 2 and an RMSE of 65.1 W m− 2, which would be probably due to the significant underestimation of α
Model sensitivity to inputs is analyzed to understand the sources of error and mechanisms of error propagation of the wind speed-independent two-source energy balance (WiTSEB). e sensitivity of latent heat flux (LE) to the ith input, Si, is defined as
Summary
Evapotranspiration (ET) plays a significant role in modeling the terrestrial hydrological cycle and energy exchange in a soil-vegetation-atmosphere system. Models using flux-profile relationship (expressed as vast temperature gradients and aerodynamic resistances) on the basis of the Monin–Obukhov Similarity (MOS) theory and energy balance theory to physically calculate LE (e.g., SEBAL [5], METRIC [6], MOD16 [7, 8], TSEB [9], HTEM [10], and STSEB [11]) or evaporation ratio (e.g., SEBS [12] and TTME [13]), are primarily proposed. Considering the different treatment of land surface, those physically based methods can be further divided into onesource methods (e.g., SEBAL, METRIC, and SEBS) and twosource methods Two-source models treat soil and vegetation as different “sources” in heat and water exchange and simulate sensible heat flux, H, and LE components differently by component temperatures (i.e., the soil and canopy temperatures), thereby representing an advancement to avoid the priori local calibration in the one-source model [9]. e twosource model is demonstrated to be robust for a wide range of landscape and hydrometeorological conditions [20,21,22,23,24]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
