Streamflow droughts and probability of their occurrence in a small agricultural catchment

Abstract

Streamfl ow droughts and probability of their occurrence in a small agricultural catchment. The goal of this work consists in quantitative analysis of the occurrence of droughts and their occurrence probability estimated for a small agricultural catchment on the basis of a multi-annual series of daily streamfl ows in the Zagodonka river at the Pachty Stare gauging station, in the context of observed changes in the stream regime during the multi-annual period 1963-2010. The Zagodonka river catchment is one of a few in Poland, with long-term records on rainfall and runoff. To identify streamfl ow droughts in daily discharge hydrograms, truncation level Q 90% (discharge determined from the fl ow duration curve) was used. Minimum duration of drought amounting to 10 days, was the additional criterion for identifi cation of droughts. The Nizowka2003 model was used for fi nding distributions of the probability of defi cit volume and duration of maximum summer droughts for the Zagodonka river. The droughts in the small agricultural catchment under study concern only summer half-years and most often they are of short duration -up to 20 days. Longer droughts, lasting lightly over 2 months, can be expected -once per 10 years. The occurrence of a summer drought lasting almost all the season in the Zagodonka river is probable once per 100 years. A weak correlation between the minimum drought discharge and their duration was found.