Detecting Similarity in Flood Seasonality of Slovak and Austrian Catchments

Abstract

The main aim of the study is the flood seasonality of Slovak and Austrian catchments in the 50-year period of 1961-2010. Flood seasonality analyses have become interesting topics for many authors worldwide. In the context of flood seasonality, the dates of annual maximum floods at 556 gauging stations across Austria (475) and Slovakia (81) were analyzed. The length of the time series of the selected gauging stations is variable, ranging from 30-50 years. We have focused on an investigation of the relationship between flood seasonality characteristic -r (the concentration of a flood around the mean date of a flood occurrence), the hydrological characteristics (long-term average air temperature (°C) for the period 1961-2010, the long-term average daily precipitation (mm) for the period 1961-2010), physiographic characteristics of catchments (catchment area (km2), and the outlet elevations (m a.s.l.)). The pooling of the catchments was processed by a nonhierarchical k-means cluster analysis and boxplot analysis. The input for the k-means cluster analysis was r (the concentration of a flood around the mean date of a flood occurrence), the long-term average daily precipitation (mm) for the period 1961-2010 for the individual catchments, the catchment area (km2), and the outlet elevations (m a.s.l.). The results show that the optimal number of clusters for the selected catchments is three and that these clusters show some similar features. Cluster one is located in the High Tatras, the Alps and the High Tauern (the long-term average air temperature is between -2 ÷ 8°C; the long-term average daily precipitation is between 3-6mm); cluster two is located in the Low Tatras and the Lower Tauern (the long-term average air temperature is between 1 ÷ 10°C, the long-term average daily precipitation between 2-4mm); and cluster three is located in the lowlands of Austria and Slovakia (the long-term average air temperature is between 5 ÷ 10°C, the long-term average daily precipitation is between 1-4mm).