Modelling surface turbulent heat fluxes over heterogeneous landscapes
Sammy Njuki is a PhD student in the Departement of Water Resources. (Co)Promotors are prof.dr. Z. Su and dr.ir. C.M.M. Mannaerts from the Faculty ITC.
This thesis addresses some of the issues encountered when modelling surface turbulent heat fluxes over heterogeneous landscapes. Quantifying surface turbulent heat fluxes is crucial in our understanding of changes in the hydrological, energy, and carbon cycles. Thus, reliable quantification of surface turbulent heat fluxes is not only crucial to the sustainable utilization and management of our ecosystems, but also critical in minimizing and mitigating social, economic, and environmental risks associated with weather and climate-induced extreme events such as floods, droughts, and heatwaves. Modelling approaches are more applicable for quantifying spatially distributed surface turbulent heat fluxes over regional and global scales than measurements owing to the sparse distribution of observation stations in most parts of the world. Often, the modelling schemes adopted rarely capture the spatial-temporal dynamics in surface characteristics introducing biases in the modelled fluxes. Some of the uncertainties in most modelling schemes emanate from unrepresentative input data, more so in heterogeneous landscapes. Cognizant to this, the ability of machine learning and physically based downscaling modelling schemes in the retrieval of high resolution model input variables in heterogeneous landscapes are evaluated. Another source of uncertainties is deficiencies in the model parameterization of the physical processes. Improvements on the physical parameterizations of heat transfer in the SEBS model which is commonly used for simulating surface turbulent heat fluxes from remote sensing data are proposed. Besides, a simplified parameterizations for simulating surface turbulent heat fluxes that does not require canopy height as an input is proposed. Since canopy height is a rather difficult variable to estimate, such a simplified approach is needed in the modelling of surface turbulent heat fluxes in heterogeneous landscapes. It is concluded from this research that reliable modelling of surface turbulent fluxes is largely dependent on how well a given modelling scheme can describe the physical processes involved given the available input data
