APPLICATION: FLOOD FORECASTING MODEL FOR KLODZKO CATCHMENT (POLAND) - Modelling Uncertainty in Flood Forecasting Systems - page 98

are available. Due to the lack of forecasted precipitation data, the observed precipitation
is assumed as a forecasted precipitation for the application of the present methodology.
The MF representing the uncertainty in the quantity of the forecasted precipitation for
each subasin is obtained by taking the error of +/!30 % in the given precipitation, i.e.
e 1 = e 2 =0.3 (Equation (5.12)). Although the error is taken arbitrarily, discussion with
experts suggested that the assumption is not too far from reality. The starting date for
simulation is 4 July 1997 at 06:00 hours, while the forecast of precipitation started on
July 6 1997 at 00:00 hours (i.e. 42 hours from the point of start of simulation).
Since the interval of the available precipitation data is 3 hours, the size of the forecast
period is also taken as 3 hours. The very short lag time between the rainfall and runoff
justifies the use of the present methodology of uncertainty assessment with
disaggregation. 3 subperiods of one hour each and 6 subperiods of half an hour each are
used for disaggregation. It is to be noted that for each forecast, only the uncertainty in the
forecast precipitation during the same forecast period is considered and no uncertainty is
assumed in the precipitation previous to the current forecast period. For example, to
forecast the flow for 3 hours, no uncertainty is assumed in all precipitation up to the time
0 hour; similarly to forecast the flow for 6 hours, no uncertainty is assumed in the
precipitation up to the time 3 hours, and so on. A total of 20 forecasts (20$3 hours=60
hours) from 6 July at 00:00 to 8 July at 09:00 have been carried out.
All the results presented and discussed here are based on the forecast at the
hydrological station Bardo on Nysa Klodzka (Fig. 5.1). Firstly, the simulation is carried
out to compute the discharge without considering any uncertainty in the precipitation.
The simulated discharge together with the corresponding observed discharge is presented
Figure 5.9. Observed and simulated discharges without considering uncertainty
in the forecasted precipitation for the period 4 to 11 July 1997. The
hour 0 refers to 4 July 1997 at 06:00 hours.