Biophysical controls of water vapour and energy fluxes: Towards the development of biome scale predictive models of evapotranspiration in the Albany Thicket, South Africa

Abstract

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 (G s ) 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 better able to simulate observed ET (root mean square error [RMSE] 0.28 mm day −1 ) than application of the Penman-Monteith equation using modelled G s (RMSE of 0.59-0.62 mm day −1 ) when average ET was 0.87 mm day −1 . The modified Priestley-Taylor equation did not perform well because ET was strongly coupled to vapour pressure deficit and surface conductance.

The use of swimming pools by bats on a game reserve in South Africa

“…The study area was originally converted to livestock farming in the early nineteenth century, but in 1999, it became an ecotourism‐focused game reserve. Subsequently, the area has reverted back to subtropical thicket communities comprising spinescent shrubs, woody creepers, tall woody shrubs, geophytes, succulents, and various grass species (Smit et al 2016, Gwate et al 2018, Achieng et al 2020, Duker et al 2020). Since then, the property has brought in and actively managed a number of megaherbivore and carnivore species, including cheetah ( Acinonyx jubatus ), lion ( Panthera leo ), elephant ( Loxodonta africana ), Cape mountain ( Equus zebra zebra ) and plains zebra ( Equus quagga ), hippopotamus ( Hippopotamus amphibius ), South African giraffe ( Giraffa camelopardalis giraffa ), Cape buffalo ( Syncerus caffer ), and several species of antelope.…”