Student Theses
Several students have completed or are completing their theses as part of this particular project. Below if a list of the work completed thus far or that is in progress
Thage, K.V (2023)
Fully integrated hydrological modelling using regression-based interpolation merging raingauge- and satellite data for the Hout-Sand catchment, South Africa. MSc thesis University of Copenhagen.
Assessment of the water balance in semi-arid and arid regions is essential for proper understanding
of variation in groundwater level and it requires robust precipitation data to estimate correct spatial
and temporal fluxes. However, the precise spatial distribution of precipitation in the Hout-Sand
catchment, South Africa, a semi-arid area in the Limpopo river basin is not known. An existing
fully integrated hydrological model for the area is enhanced by replacing the original precipitation
product of coarse Thiessen polygons with a new product derived from rain gauge data and the
satellite precipitation product IMERG using the regression-based interpolation (RBI) method
followed by an auto-calibration. In the pre-analysis for the RBI, we found IMERG to perform
better in a point-to-pixel- and covariate analysis than the satellite products ERA5 and TAMSAT
for the period 2008-2019.
Here we show that the new precipitation product simulates a more realistic spatial distribution of
the actual evapotranspiration (ET) than the Thiessen polygons, and that the new product is more
adapted to the catchment than IMERG both spatially and seasonally. This affects all water fluxes
resulting in precipitation events correlating more with changes in observed head elevation in the
saturated zone (SZ) than the Thiessen polygons for locations far from the rain gauge stations. We
found actual ET to be 93.5% of mean annual precipitation (MAP) and recharge to the SZ to be
2.9%MAP. The ET is slightly higher than previous studies estimate, while the recharge is
comparable. The model proved unable to simulate correct discharge and head elevation in SZ due
to falsely simulated exchange of water from the SZ to the river, an absence of overland flow and
no variation in the head elevation. These results demonstrate how hydrological models of sparse
catchments, like the Hout-Sand, are sensitive to how the hydrogeological characteristics are
implemented in the conceptual model as well as the impact spatiotemporal information from
satellite products have on components otherwise lacking data in a hydrological model.
Aaes, A.H. (2023)
Fully integrated hydrological modelling using NDVI as a proxy for spatiotemporal agricultural field variation in the Hout-Sand catchment, South Africa. MSc thesis University of Copenhagen.
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Groundwater is a fundamental component of the global hydroclimatic system and plays a central
role in sustaining water supplies and livelihoods. The Hout and Sand catchments, South Africa,
have a long history of commercial potato cultivation heavily dependent on intensive groundwaterfed
center pivot irrigation.
However, the temporal variability of the cultivated agricultural practices are poorly documented.
Based on Landsat remote sensing data, NDVI time series were computed for the fields in 2008-
2019. An NDVI-threshold value of 0.7 was used to determine whether each field was active a
given year. An existing fully integrated hydrological model for the area was improved with the
data and subsequently object for an OSTRICH-autocalibration. The modified irrigation input
showed that irrigation is higher than earlier anticipated. The absolute change was too small to
measure in the water balance of the whole catchment area. Nevertheless, the cultivated agricultural
field activity showed moderate spatial autocorrelation with agricultural fields being more
frequently active in the southern part of the catchment. The model was calibrated with RMSE for
the simulated groundwater head elevations, and the Pearson correlation coefficient, high flow
event frequency, bias term, and flow variability error for discharge. The model’s simulated high
flow event discharge improved, however a constant inflow from the saturated zone to the riverbed
caused the baseflow to be higher than observations. A confining aquifer lens implemented around
the river did not completely limit the inflow to the river. The model proved unable to simulate
accurate head elevations in the saturated zone. The results emphasize the inbound parameter
sensitivity when setting up hydrological models in data-sparse environments, and that improved
data inputs as well as a change in the conceptualization of the model framework is required.
Vejby J (2021)
Remote sensing pilot study for Waterpoort, South Africa; Correlation of SAR and NDVI, BSc Thesis, University of Copenhagen
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Andersen ME (2021)
Fully integrated hydrological Mike SHE model of the Hout/Sand river
catchment in South Africa, MSc Thesis, University of Copenhagen.
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