Extending periodic eddy covariance latent heat fluxes through tree sap-flow measurements to estimate long-term total evaporation in a peat swamp forest

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dc.contributor.authorClulow, A D
dc.contributor.authorEverson, C S
dc.contributor.authorMengistu, M G
dc.contributor.authorPrice, J S
dc.contributor.authorNickless, A
dc.contributor.authorJewitt, G P W
dc.date.accessioned2021-10-08T07:04:14Z
dc.date.available2021-10-08T07:04:14Z
dc.date.issued2015
dc.description.abstractA combination of measurement and modelling was used to find a pragmatic solution to estimate the annual total evaporation from the rare and indigenous Nkazana Peat Swamp Forest (PSF) on the east coast of Southern Africa to improve the water balance estimates within the area. Actual total evaporation (ET<sub>a</sub>) was measured during three window periods (between 7 and 9 days each) using an eddy covariance (EC) system on a telescopic mast above the forest canopy. Sap flows of an understory tree and an emergent tree were measured using a low-maintenance heat pulse velocity system for an entire hydrological year (October 2009 to September 2010). An empirical model was derived, describing the relationship between ET<sub>a</sub> from the Nkazana PSF and sap-flow measurements. These overlapped during two of the window periods (<i>R</i><sup>2</sup> = 0.92 and 0.90), providing hourly estimates of ET<sub>a</sub> from the Nkazana PSF for a year, totalling 1125 mm (while rainfall was 650 mm). In building the empirical model, it was found that to include the understory tree sap flow provided no benefit to the model performance. In addition, the relationship between the emergent tree sap flow with ET<sub>a</sub> between the two field campaigns was consistent and could be represented by a single empirical model (<i>R</i><sup>2</sup> = 0.90; RMSE = 0.08 mm h<sup>−1</sup>). <br><br> During the window periods of EC measurement, no single meteorological variable was found to describe the Nkazana PSF ET<sub>a</sub> satisfactorily. However, in terms of evaporation models, the hourly FAO Penman–Monteith reference evaporation (ET<sub>o</sub>) best described ET<sub>a</sub> during the August 2009 (<i>R</i><sup>2</sup> = 0.75), November 2009 (<i>R</i><sup>2</sup> = 0.85) and March 2010 (<i>R</i><sup>2</sup> = 0.76) field campaigns, compared to the Priestley–Taylor potential evaporation (ET<sub>p</sub>) model (<i>R</i><sup>2</sup> = 0.54, 0.74 and 0.62 during the respective field campaigns). From the extended record of ET<sub>a</sub> (derived in this study from sap flow) and ET<sub>o</sub>, a monthly crop factor (<i>K</i><sub>c</sub>) was derived for the Nkazana PSF, providing a method of estimating long-term swamp forest water-use from meteorological data. The monthly <i>K</i><sub>c</sub> indicated two distinct periods. From February to May, it was between 1.2 and 1.4 compared with June to January, when the crop factor was 0.8 to 1.0. The derived monthly <i>K</i><sub>c</sub> values were verified as accurate (to one significant digit) using historical data measured at the same site, also using EC, from a previous study. <br><br> The measurements provided insights into the microclimate within a subtropical peat swamp forest and the contrasting sap flow of emergent and understory trees. They showed that expensive, high-maintenance equipment can be used during manageable window periods in conjunction with low-maintenance systems, dedicated to individual trees, to derive a model to estimate long-term ET<sub>a</sub> over remote heterogeneous forests. In addition, the contrast in annual ET<sub>a</sub> and rainfall emphasised the reliance of the Nkazana PSF on groundwater.
dc.identifier.apacitationClulow, A. D., Everson, C. S., Mengistu, M. G., Price, J. S., Nickless, A., & Jewitt, G. P. W. (2015). Extending periodic eddy covariance latent heat fluxes through tree sap-flow measurements to estimate long-term total evaporation in a peat swamp forest. <i>Hydrology and Earth System Sciences</i>, 19(5), 2513 - 2534. http://hdl.handle.net/11427/34458en_ZA
dc.identifier.chicagocitationClulow, A D, C S Everson, M G Mengistu, J S Price, A Nickless, and G P W Jewitt "Extending periodic eddy covariance latent heat fluxes through tree sap-flow measurements to estimate long-term total evaporation in a peat swamp forest." <i>Hydrology and Earth System Sciences</i> 19, 5. (2015): 2513 - 2534. http://hdl.handle.net/11427/34458en_ZA
dc.identifier.citationClulow, A.D., Everson, C.S., Mengistu, M.G., Price, J.S., Nickless, A. & Jewitt, G.P.W. 2015. Extending periodic eddy covariance latent heat fluxes through tree sap-flow measurements to estimate long-term total evaporation in a peat swamp forest. <i>Hydrology and Earth System Sciences.</i> 19(5):2513 - 2534. http://hdl.handle.net/11427/34458en_ZA
dc.identifier.issn1027-5606
dc.identifier.issn1607-7938
dc.identifier.ris TY - Journal Article AU - Clulow, A D AU - Everson, C S AU - Mengistu, M G AU - Price, J S AU - Nickless, A AU - Jewitt, G P W AB - A combination of measurement and modelling was used to find a pragmatic solution to estimate the annual total evaporation from the rare and indigenous Nkazana Peat Swamp Forest (PSF) on the east coast of Southern Africa to improve the water balance estimates within the area. Actual total evaporation (ET<sub>a</sub>) was measured during three window periods (between 7 and 9 days each) using an eddy covariance (EC) system on a telescopic mast above the forest canopy. Sap flows of an understory tree and an emergent tree were measured using a low-maintenance heat pulse velocity system for an entire hydrological year (October 2009 to September 2010). An empirical model was derived, describing the relationship between ET<sub>a</sub> from the Nkazana PSF and sap-flow measurements. These overlapped during two of the window periods (<i>R</i><sup>2</sup> = 0.92 and 0.90), providing hourly estimates of ET<sub>a</sub> from the Nkazana PSF for a year, totalling 1125 mm (while rainfall was 650 mm). In building the empirical model, it was found that to include the understory tree sap flow provided no benefit to the model performance. In addition, the relationship between the emergent tree sap flow with ET<sub>a</sub> between the two field campaigns was consistent and could be represented by a single empirical model (<i>R</i><sup>2</sup> = 0.90; RMSE = 0.08 mm h<sup>−1</sup>). <br><br> During the window periods of EC measurement, no single meteorological variable was found to describe the Nkazana PSF ET<sub>a</sub> satisfactorily. However, in terms of evaporation models, the hourly FAO Penman–Monteith reference evaporation (ET<sub>o</sub>) best described ET<sub>a</sub> during the August 2009 (<i>R</i><sup>2</sup> = 0.75), November 2009 (<i>R</i><sup>2</sup> = 0.85) and March 2010 (<i>R</i><sup>2</sup> = 0.76) field campaigns, compared to the Priestley–Taylor potential evaporation (ET<sub>p</sub>) model (<i>R</i><sup>2</sup> = 0.54, 0.74 and 0.62 during the respective field campaigns). From the extended record of ET<sub>a</sub> (derived in this study from sap flow) and ET<sub>o</sub>, a monthly crop factor (<i>K</i><sub>c</sub>) was derived for the Nkazana PSF, providing a method of estimating long-term swamp forest water-use from meteorological data. The monthly <i>K</i><sub>c</sub> indicated two distinct periods. From February to May, it was between 1.2 and 1.4 compared with June to January, when the crop factor was 0.8 to 1.0. The derived monthly <i>K</i><sub>c</sub> values were verified as accurate (to one significant digit) using historical data measured at the same site, also using EC, from a previous study. <br><br> The measurements provided insights into the microclimate within a subtropical peat swamp forest and the contrasting sap flow of emergent and understory trees. They showed that expensive, high-maintenance equipment can be used during manageable window periods in conjunction with low-maintenance systems, dedicated to individual trees, to derive a model to estimate long-term ET<sub>a</sub> over remote heterogeneous forests. In addition, the contrast in annual ET<sub>a</sub> and rainfall emphasised the reliance of the Nkazana PSF on groundwater. DA - 2015 DB - OpenUCT DP - University of Cape Town IS - 5 J1 - Hydrology and Earth System Sciences LK - https://open.uct.ac.za PY - 2015 SM - 1027-5606 SM - 1607-7938 T1 - Extending periodic eddy covariance latent heat fluxes through tree sap-flow measurements to estimate long-term total evaporation in a peat swamp forest TI - Extending periodic eddy covariance latent heat fluxes through tree sap-flow measurements to estimate long-term total evaporation in a peat swamp forest UR - http://hdl.handle.net/11427/34458 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/34458
dc.identifier.vancouvercitationClulow AD, Everson CS, Mengistu MG, Price JS, Nickless A, Jewitt GPW. Extending periodic eddy covariance latent heat fluxes through tree sap-flow measurements to estimate long-term total evaporation in a peat swamp forest. Hydrology and Earth System Sciences. 2015;19(5):2513 - 2534. http://hdl.handle.net/11427/34458.en_ZA
dc.language.isoeng
dc.publisher.departmentDepartment of Statistical Sciences
dc.publisher.facultyFaculty of Science
dc.sourceHydrology and Earth System Sciences
dc.source.journalissue5
dc.source.journalvolume19
dc.source.pagination2513 - 2534
dc.source.urihttps://dx.doi.org/10.5194/hess-19-2513-2015
dc.subject.otherBurns
dc.subject.otherDisaster Planning
dc.subject.otherHumans
dc.subject.otherMass Casualty Incidents
dc.subject.otherNational Health Programs
dc.subject.otherPractice Guidelines as Topic
dc.subject.otherSocieties, Medical
dc.subject.otherSouth Africa
dc.titleExtending periodic eddy covariance latent heat fluxes through tree sap-flow measurements to estimate long-term total evaporation in a peat swamp forest
dc.typeJournal Article
uct.type.publicationResearch
uct.type.resourceJournal Article
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