Seasonal concentration time of hydrological drought in Poland

Abstract

The time of hydrological drought concentration was estimated based on Markham’s indices. The research material consisted of a series of daily discharges from the period of 1985-2014 obtained from 79 cross sections of stream gauges distributed along rivers in Poland. In the first stage of the research, low-flow episodes were identified at the threshold level of Q70%, derived from the flow duration curve. Drought streamflow deficit volumes were calculated and assigned to monthly intervals. On this basis, the hydrological drought concentration time index and the hydrological drought seasonality index were assessed for particular years and for the whole study period. Spatial and temporal analysis was carried out on both characteristics, paying particular attention to a number of factors determining the investigated phenomenon and the long-term stability of hydrological drought concentration time.