| To assess the prognostic values concerning precipitation and air temperature
in the river catchment area of the Ilm/Thuringia issued by the German
Meteorological Service, the differences between the prognostic values and
related measured values were statistically evaluated. The investigations
covered the period from November 1999 to December 2003. The spatial
resolution corresponds to the LM grid cells and the available data. The
observed precipitation values were corrected with regard to systematic wind
error in dependence of temperature.
The forecast data were investigated comprehensively in order to quantify the
statistical reliability. Therefore, the 2nd moment as the case may be the
standard deviation of the differences between observed precipitation values
and forecasting precipitation values have been calculated. The
investigations were subdivided into the complete stretch of time, the
hydrological summer and the hydrological winter. Each measured value was
analysed with regard to the 12-, 24-, 36- and 48-hour forecast made by the
DWD.
As a result, empirical analytical functions were developed to describe
adequately the statistical quantities for standard deviation of
precipitation and temperature for the periods of hydrological summer and
hydrological winter in dependence on forecasting time, mean ground level and
roughness (fractal dimension) of the LM-grid cell. |