Exceedance probability of characteristic flows in Poland

Abstract

Aim of the study: The goals of this paper are: to determine the empirical exeedance probability of the characteristic flows Qchar (SNQ, WNQ, NSQ, SSQ, WSQ, NWQ and SWQ) in Poland; to link the flows Qchar with quantiles Qp and to examine the relationship between the empirical exeedance probability of the flow Qchar from: Qp, the catchment area A and the gauging station elevation H. Material and methods: Characteristic flows were calculated on the basis of 50-year daily flow time series (from November 1, 1971 to October 31, 2021) in 355 gauging cross-sections located throughout Poland. The empirical exeedance probabilities of the flows Qchar are presented in graphs, and their spatial distribution – in maps. In order to assess the relationship between the variables Qchar and Qp, Qchar and A, and Qchar and H, Spearman’s rank correlations were examined. Results and conclusions: The results of the research allowed to assign (approximately) in Poland to the characteristic flows Qchar quantiles Qp: SNQ – Q93%, WNQ – Q63%, NSQ – Q74%, SSQ – Q33%, WSQ – Q10%, NWQ – Q26% i SWQ – Q1,3%. The analyzes showed that in some cases the variability of the empirical exceedance probability of a given characteristic flow is so high that it would be appropriate to assign Qchar to one value Qp together with information about the measurement error. The analysis of correlations and maps shows, above all, a significant dependence of the exceedance probability of the flows Qchar on the gauging station elevation H – in some cases it is a positive relationship, in some – negative.

Keywords

• characteristic flow
• probable flow
• exceedance probability
• flow duration curve