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Journal of Arid Land  2019, Vol. 11 Issue (4): 495-512    DOI: 10.1007/s40333-019-0098-2
Comparison of two remote sensing models for estimating evapotranspiration: algorithm evaluation and application in seasonally arid ecosystems in South Africa
DZIKITI Sebinasi1,*(), Z JOVANOVIC Nebo1, DH BUGAN Richard1, RAMOELO Abel2, P MAJOZI Nobuhle2, NICKLESS Alecia2, A CHO Moses2, C LE MAITRE David1, NTSHIDI Zanele1, H PIENAAR Harrison1
1Council for Scientific and Industrial Research, Natural Resources and Environment, Stellenbosch 7599, South Africa
2Council for Scientific and Industrial Research, Natural Resources and Environment, Pretoria 0001, South Africa
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Remote sensing tools are becoming increasingly important for providing spatial information on water use by different ecosystems. Despite significant advances in remote sensing based evapotranspiration (ET) models in recent years, important information gaps still exist on the accuracy of the models particularly in arid and semi-arid environments. In this study, we evaluated the Penman-Monteith based MOD16 and the modified Priestley-Taylor (PT-JPL) models at the daily time step against three measured ET datasets. We used data from two summer and one winter rainfall sites in South Africa. One site was dominated by native broad leaf and the other by fine leafed deciduous savanna tree species and C4 grasses. The third site was in the winter rainfall Cape region and had shrubby fynbos vegetation. Actual ET was measured using open-path eddy covariance systems at the summer rainfall sites while a surface energy balance system utilizing the large aperture boundary layer scintillometer was used in the Cape. Model performance varied between sites and between years with the worst estimates (R2<0.50 and RMSE>0.80 mm/d) observed during years with prolonged mid-summer dry spells in the summer rainfall areas. Sensitivity tests on MOD16 showed that the leaf area index, surface conductance and radiation budget parameters had the largest effect on simulated ET. MOD16 ET predictions were improved by: (1) reformulating the emissivity expressions in the net radiation equation; (2) incorporating representative surface conductance values; and (3) including a soil moisture stress function in the transpiration sub-model. Implementing these changes increased the accuracy of MOD16 daily ET predictions at all sites. However, similar adjustments to the PT-JPL model yielded minimal improvements. We conclude that the MOD16 ET model has the potential to accurately predict water use in arid environments provided soil water stress and accurate biome-specific parameters are incorporated.

Key wordsMOD16 ET      drought stress      model validation      Penman-Monteith      Priestley-Taylor      sensitivity analysis     
Received: 28 December 2017      Published: 10 August 2019
Fund:  This work was supported by the South African Parliamentary Grant to the Council for Scientific and Industrial Research Project (ECHS014, EEEO024, ECHS058 and ECHS052)
Corresponding Authors: DZIKITI Sebinasi     E-mail:
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The first and second authors contributed equally to this work.

Cite this article:

DZIKITI Sebinasi, Z JOVANOVIC Nebo, DH BUGAN Richard, RAMOELO Abel, P MAJOZI Nobuhle, NICKLESS Alecia, A CHO Moses, C LE MAITRE David, NTSHIDI Zanele, H PIENAAR Harrison. Comparison of two remote sensing models for estimating evapotranspiration: algorithm evaluation and application in seasonally arid ecosystems in South Africa. Journal of Arid Land, 2019, 11(4): 495-512.

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