The Risk of Extreme Streamflow Drought in the Polish Carpathians—A Two-Dimensional Approach

Poland has relatively small water resources compared to other European countries. Droughts are a characteristic feature of the Polish climate; however, recent years have been particularly warm, causing longer and more severe droughts, including streamflow droughts. The most unfavourable streamflow droughts, considering the economic or social (including health-related) consequences, are the longest and/or the ones with the largest volumes. Such prolonged and severe droughts may constitute a natural disaster threatening public health. The main aim of this article was to define the spatial variability of the annual maximum streamflow drought in the Polish Carpathians and the risk of the maximum streamflow drought of a duration and volume exceeding the given value occurring in this region. This was conducted based on a 30-year time series of daily flows in selected gauging cross sections on rivers in the Polish Carpathians. One- and-two-dimensional probability distributions (utilising a copula function) of the two most important maximum streamflow drought characteristics were identified, specifically duration and volume, which, in consequence, led to identifying the maximum streamflow droughts of a given return period (a given risk level). Maps of maximum streamflow drought hazard were developed and understood as spatial distributions of the maximum streamflow drought frequency of duration and volume exceeding the annual given values. Analysis of the maps allowed for the selection of areas/basins being more or less at risk of extreme annual streamflow drought of a duration and/or volume exceeding the given value.