Hydrological modelling of the Zambezi catchment for ... - TU Delft

SUMMARY
The second rainfall-algorithm is the FEWS RFE 1.0. This algorithm first estimates the rainfall
based on thermal Infrared data with the GPI-algorithm. Next, the estimates are corrected by
fitting the values to ground stations. Finally, an orographic lifting and humidity model is
applied on the estimates. A comparison between the RFE 1.0 estimates and the observed data
shows that the algorithm overestimates the rainfall somewhat. However, the correlation
coefficient is 0.85, which is quite low compared to the other algorithms.
The last algorithm, which has been investigated, is the FEWS RFE 2.0. This algorithm first
estimates the rainfall separately on three satellite sources: Special Sensor Microwave/Imager,
AMSU-A microwave and METEOSAT Infrared. Next the estimated are weighted to reduce
the error. The last step is to correct the weighted estimates with observed data. The
performance of the RFE 2.0 is very good, with a correlation coefficient of 0.97 and a very
little overestimation.
Finally after a comparison between the algorithms, the corrected MIRA-algorithm is chosen
for the period 1993-2000 and the FEWS RFE 2.0 for the period 2001-2003. For the period
before 1993 interpolated rainfall data from ground stations is used.
The hydrological model, which is built, consists of two sub models: a water balance model
created in STREAM and a Muskingum routing model. The water balance model is a storage
reservoir model, which contains three levels. First, the shallow soil from where interception
takes place. Second, the unsaturated zone with the transpiration process and third, the
saturated zone. From the saturated zone three ground water outflows are implemented: the
saturation overland flow, the quick flow and the slow flow.
The model is only calibrated for the western part of the catchment on the locations Lukulu
and Victoria Falls, because in the western part less influence of tides exists. Looking at the
results it can be concluded that the model is quite reasonable in simulating the discharge with
a Nash-Suttcliffe coefficient of 0.70 and 0.68 for Lukulu and Victoria Falls respectively.
However the model underestimates the discharge slightly, especially the high peaks.
GLUE
To obtain more knowledge about the sensitivity of the model, the GLUE-procedure (Beven,
1989) is used twice. First, the procedure is carried out on the uncertainty of four parameters
and second, the procedure was executed for the uncertainty in the precipitation and potential
evaporation input data of the Zambezi model.
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