Évaluation de l'intensité de pluies des espaces à données manquantes

Assessment of rain intensity in locations for which data are missing

Collaborateur scientifique à l'Institut Hydrographique Centre de Recherches des Ressources Hydrauliques (VITUKI) Budapest, Hongrie

Abstract

The results obtained by processing the data of conventional and recording rain gages are presented. These were used for deriving a relationship of general validity by which rain intensities can be estimated for certain regions with incomplete data. The data of rain gages with long (round 20 years) records available were examined to approximate the empirical distributions of annual greatest rainfalls of different (1, 2, ... 6, 12 days) durations by different distribution functions. Along with the observation data, the charts of recording rain gages were also processed and analysed, determining as accurate1y as the chart would permit the rain intensities by 30' time intervals for the period on record up to 1974. (During the last years the 30/ intervals could be resolved into 5 and 15 minutes) In the way, 10-20 years intensity time series were produced for round 10 stations. From the charts of the individual stations, we have determined the rain intensities of different probability during the annual maxima of 0.5, 1, 2 ... hours and 1, 2, ... 6, 12 days duration. In an intensity vs. time diagram these values plotted to a straight line (Fig. 1), implying that the rain intensities of short (few hours) and longer (few days) duration are described by a single function at a particular station. This result can be extended to rain gaging stations (having no recording gage), where a sufficient1y long observation record is availab1e. By extrapolating the function it is thus possible to estimate the intensity of rains shorter than one day for a particular station. The slope of the rain intensity functions was found to be related to the normal average annual rainfall at the station. The functions at stations with little annual rainfall were very steep relative to the fiat functions of the stations with abundant rainfall (Fig. 2).