Modelling evapotranspiration using the modified Penman-Monteith equation and MODIS data over the Albany Thicket in South Africa

Lesley Gibson

    Research output: Chapter in Book/Report/Conference proceedingConference contribution

    44 Downloads (Pure)

    Abstract

    Evapotranspiration (ET) is one of the least understood components of the water cycle, particularly in data scarce areas. In a context of climate change, evaluating water vapour fluxes of a particular area is crucial to help understand dynamics in water balance. In data scarce areas, ET modelling becomes vital. The study modelled ET using the Penman-Monteith-Leuning (PML) equation forced by Moderate Resolution Imaging Spectroradiometer (MODIS) leaf area index (LAI) and MODIS albedo with ancillary meteorological data from an automatic weather station. The study area is located on the Albany Thicket (AT) biome of South Africa and the dominant plant species is Portulacaria afra. The biggest challenge to the implementation of the PML is the parameterisation of surface and stomatal conductance. We tested the use of volumetric soil water content (f_SWC), precipitation and equilibrium evaporation ratio (f_zhang) and soil drying after precipitation (f_drying) approaches to account for the fraction (f) of evaporation from the soil. ET from the model was validated using an eddy covariance system (EC). Post processing of eddy covariance data was implement using EddyPro software. Thef_drying method performed better with a root mean square observations standard deviation ratio (RSR) of 0.97. The results suggest that modelling ET over the AT vegetation is delicate owing to strong vegetation phenological control of the ET process. The convergent evolution of the vegetation has resulted in high plant available water than the model can detect. It is vital to quantify plant available water in order to improve ET modelling in thicket vegetation.
    Original languageEnglish
    Title of host publicationProc. SPIE 9998, Remote Sensing for Agriculture, Ecosystems, and Hydrology XVIII
    EditorsChristopher M. U. Neale, Antonini Maltese
    PublisherSPIE
    Number of pages20
    Volume9998
    ISBN (Print)9781510604001
    DOIs
    Publication statusPublished - 25 Oct 2016

    Fingerprint

    Penman-Monteith equation
    MODIS
    evapotranspiration
    modeling
    vegetation
    eddy covariance
    evaporation
    convergent evolution
    weather station
    stomatal conductance
    biome
    Africa
    leaf area index
    water
    albedo
    water budget
    parameterization
    water vapor
    soil
    soil water

    Keywords

    • Penman Monteith equation
    • ET modelling
    • Portulacaria afra
    • soil science

    Cite this

    Gibson, L. (2016). Modelling evapotranspiration using the modified Penman-Monteith equation and MODIS data over the Albany Thicket in South Africa. In C. M. U. Neale, & A. Maltese (Eds.), Proc. SPIE 9998, Remote Sensing for Agriculture, Ecosystems, and Hydrology XVIII (Vol. 9998). SPIE. https://doi.org/10.1117/12.2245439
    Gibson, Lesley. / Modelling evapotranspiration using the modified Penman-Monteith equation and MODIS data over the Albany Thicket in South Africa. Proc. SPIE 9998, Remote Sensing for Agriculture, Ecosystems, and Hydrology XVIII. editor / Christopher M. U. Neale ; Antonini Maltese. Vol. 9998 SPIE, 2016.
    @inproceedings{69f4ab94f2814d3d8c03e5a19bc929d3,
    title = "Modelling evapotranspiration using the modified Penman-Monteith equation and MODIS data over the Albany Thicket in South Africa",
    abstract = "Evapotranspiration (ET) is one of the least understood components of the water cycle, particularly in data scarce areas. In a context of climate change, evaluating water vapour fluxes of a particular area is crucial to help understand dynamics in water balance. In data scarce areas, ET modelling becomes vital. The study modelled ET using the Penman-Monteith-Leuning (PML) equation forced by Moderate Resolution Imaging Spectroradiometer (MODIS) leaf area index (LAI) and MODIS albedo with ancillary meteorological data from an automatic weather station. The study area is located on the Albany Thicket (AT) biome of South Africa and the dominant plant species is Portulacaria afra. The biggest challenge to the implementation of the PML is the parameterisation of surface and stomatal conductance. We tested the use of volumetric soil water content (f_SWC), precipitation and equilibrium evaporation ratio (f_zhang) and soil drying after precipitation (f_drying) approaches to account for the fraction (f) of evaporation from the soil. ET from the model was validated using an eddy covariance system (EC). Post processing of eddy covariance data was implement using EddyPro software. Thef_drying method performed better with a root mean square observations standard deviation ratio (RSR) of 0.97. The results suggest that modelling ET over the AT vegetation is delicate owing to strong vegetation phenological control of the ET process. The convergent evolution of the vegetation has resulted in high plant available water than the model can detect. It is vital to quantify plant available water in order to improve ET modelling in thicket vegetation.",
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    Gibson, L 2016, Modelling evapotranspiration using the modified Penman-Monteith equation and MODIS data over the Albany Thicket in South Africa. in CMU Neale & A Maltese (eds), Proc. SPIE 9998, Remote Sensing for Agriculture, Ecosystems, and Hydrology XVIII. vol. 9998, SPIE. https://doi.org/10.1117/12.2245439

    Modelling evapotranspiration using the modified Penman-Monteith equation and MODIS data over the Albany Thicket in South Africa. / Gibson, Lesley.

    Proc. SPIE 9998, Remote Sensing for Agriculture, Ecosystems, and Hydrology XVIII. ed. / Christopher M. U. Neale; Antonini Maltese. Vol. 9998 SPIE, 2016.

    Research output: Chapter in Book/Report/Conference proceedingConference contribution

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    AU - Gibson, Lesley

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    Y1 - 2016/10/25

    N2 - Evapotranspiration (ET) is one of the least understood components of the water cycle, particularly in data scarce areas. In a context of climate change, evaluating water vapour fluxes of a particular area is crucial to help understand dynamics in water balance. In data scarce areas, ET modelling becomes vital. The study modelled ET using the Penman-Monteith-Leuning (PML) equation forced by Moderate Resolution Imaging Spectroradiometer (MODIS) leaf area index (LAI) and MODIS albedo with ancillary meteorological data from an automatic weather station. The study area is located on the Albany Thicket (AT) biome of South Africa and the dominant plant species is Portulacaria afra. The biggest challenge to the implementation of the PML is the parameterisation of surface and stomatal conductance. We tested the use of volumetric soil water content (f_SWC), precipitation and equilibrium evaporation ratio (f_zhang) and soil drying after precipitation (f_drying) approaches to account for the fraction (f) of evaporation from the soil. ET from the model was validated using an eddy covariance system (EC). Post processing of eddy covariance data was implement using EddyPro software. Thef_drying method performed better with a root mean square observations standard deviation ratio (RSR) of 0.97. The results suggest that modelling ET over the AT vegetation is delicate owing to strong vegetation phenological control of the ET process. The convergent evolution of the vegetation has resulted in high plant available water than the model can detect. It is vital to quantify plant available water in order to improve ET modelling in thicket vegetation.

    AB - Evapotranspiration (ET) is one of the least understood components of the water cycle, particularly in data scarce areas. In a context of climate change, evaluating water vapour fluxes of a particular area is crucial to help understand dynamics in water balance. In data scarce areas, ET modelling becomes vital. The study modelled ET using the Penman-Monteith-Leuning (PML) equation forced by Moderate Resolution Imaging Spectroradiometer (MODIS) leaf area index (LAI) and MODIS albedo with ancillary meteorological data from an automatic weather station. The study area is located on the Albany Thicket (AT) biome of South Africa and the dominant plant species is Portulacaria afra. The biggest challenge to the implementation of the PML is the parameterisation of surface and stomatal conductance. We tested the use of volumetric soil water content (f_SWC), precipitation and equilibrium evaporation ratio (f_zhang) and soil drying after precipitation (f_drying) approaches to account for the fraction (f) of evaporation from the soil. ET from the model was validated using an eddy covariance system (EC). Post processing of eddy covariance data was implement using EddyPro software. Thef_drying method performed better with a root mean square observations standard deviation ratio (RSR) of 0.97. The results suggest that modelling ET over the AT vegetation is delicate owing to strong vegetation phenological control of the ET process. The convergent evolution of the vegetation has resulted in high plant available water than the model can detect. It is vital to quantify plant available water in order to improve ET modelling in thicket vegetation.

    KW - Penman Monteith equation

    KW - ET modelling

    KW - Portulacaria afra

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    M3 - Conference contribution

    SN - 9781510604001

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    Gibson L. Modelling evapotranspiration using the modified Penman-Monteith equation and MODIS data over the Albany Thicket in South Africa. In Neale CMU, Maltese A, editors, Proc. SPIE 9998, Remote Sensing for Agriculture, Ecosystems, and Hydrology XVIII. Vol. 9998. SPIE. 2016 https://doi.org/10.1117/12.2245439