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Validation and use of satellite derived evapotranspiration estimates in semi-arid regions of South Africa

Student:Nobuhle Patience Majozi
Timeline:March 2013 - 4 March 2018

Global estimates of evapotranspiration approximate it at 60‐65% of precipitation, whereas in arid and semi‐arid regions potential evapotranspiration is significantly higher than precipitation. ET governs the Earth’s energy and water balance through its direct association with latent heat flux; it consumes of large amounts of energy during the conversion of liquid water to vapour, hence playing an important role in hydrology, agriculture, climatology and meteorology. Accurate estimates of ET contribute to certainty in quantification of the catchment water balance and facilitate a variety of operational and management actions in sustainable water resource management. They also improve understanding of the state, spatial and temporal variability of this significant component of the water cycle at regional and/ or continental scales. 

Quantification of South Africa’s renewable water resources is a major challenge for researchers and water managers due to scarce and/or inadequate data. Hence, the need to explore the use of additional data sources, like remote sensing data and derived products, for water resources management.

This study aims to improve the estimation of ET for semi‐arid South African ecosystems using remote sensing techniques, and using the product to improve on catchment water balances. Focus will first be on validating different remote sensing based evapotranspiration algorithms (SCOPE, SEBS, SEBAL/ METRIC, Ts‐VI) and the global ET products (MOD16 and LSA‐SAF ET) using local flux tower and scintillometer data. Sensitivity analysis will be done on selected model parameters, including spatial sensitivity analysis, to determine how the remote sensing based model input uncertainties affect the model output. ET estimation for this region will then be improved through the use of local meteorological and land cover data in combination with remote sensing data, and exploring the use of soil moisture data to constrain the ET model.

The improved remote sensing based ET product will be used and evaluated for catchment water balance and water resources assessment, either as an input, or to constrain the model, in order to evaluate catchment water balance components. An adequate spatial and timely evaluation of ET losses at the catchment scale in combination with other hydrological data is important geo-information for water managers and water permit issuing in South Africa.

Top: Skukuza Flux tower, Kruger National Park, South Africa 

Meet the team

N.P. Majozi (Nobuhle Patience)
Graduate Student
Prof. Dr. W. Verhoef
Promotor
dr.ir. C.M.M. Mannaerts (Chris)
Co-promotor
Research theme
Water Cycle and Climate

Water, food and energy security and environmental safety are key challenges to our societies. “Information on water quantity and quality and their variation is urgently needed for national policies and management strategies, as well as for UN conventions on climate and sustainable development, and the achievement of the Millennium Goals”.

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