Bio-physical controls of water vapour and energy fluxes: towards the development of biome scale predictive models of evapotranspiration in the Albany Thicket, South Africa.

Onalenna Gwate, Sukhmani Mantel, Anthony Palmer, Lesley Gibson

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

An understanding of factors modulating water and energy fluxes partitioning over vegetated surfaces is important in a context of global environmental changes. The study evaluated the patterns of water vapour and energy fluxes to enable the development of biome scale predictive evapotranspiration (ET) models over the Albany Thicket vegetation. Environmental constraints to ET were assessed by examining the response of ET to biotic and abiotic factors with the latter accounting for >50% variability in ET. Bulk parameters were used to evaluate the integrated impact of biophysical factors on fluxes. The surface conductance (Gs) for use in the Penman-Monteith equation and the Priestley-Taylor coefficient (α) for application in the modified Priestley-Taylor model were modelled as a function of environmental variables. A predictive ET equation developed for the area was validated. On an annual scale, 62% of net radiation was consumed by sensible heat flux and α was < 1, indicating that the area was water limited. The decoupling factor (0.005) suggested strong connection between the canopy and the boundary layer. The patterns of ET and vapour pressure deficit suggest strong ET control through stomatal conductance. The prediction of ET as a function of leaf area index and reference evapotranspiration was able to simulate observed ET (RMSE 0.28 day-1) than application of the Penman-Monteith equation using modelled Gs (RMSE of 0.59 – 0.62 mm day-1) when average ET was 0.87 mm day-1. The modified Priestly-Taylor equation did not perform well since ET was strongly coupled to vapour pressure deficit and surface conductance.
Original languageEnglish
Article numbere2031
JournalEcohydrology
Volume11
Issue number8
Early online date16 Aug 2018
DOIs
Publication statusPublished - 2 Dec 2018

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