Basing on four 49-year time series of daily flows in the Mała Wisła catchment, the influence of the adopted POT-type drought definition on the stationarity of four drought characteristics: drought starting time, inter-drought time , duration T and deficit V, as well as their mean characteristics were investigated. The drought definition depended on three parameters: p, Tmin and min, i.e., the mean percent exceedance time of the given threshold flow Qp (p = 60, 70, 80 i 90%), minimum drought duration T¬min and minimum inter-drought time min; (Tmin, min) = (7;7), (14;7) and (14;14) days. The mean characteristics exhibited regular (in some cases very regular) dependence on p. It was shown that the monthly average number of drought starting times has clear minimum in March, and the null hypothesis on the zero slope value of the time regression for the remaining three characteristics, , T and V may be accepted in most cases.
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For adopted 12 drought definitions and basing on 49-year time series of daily flows at four cross-sections in the Mała Wisła catchment, it was found that the probability distributions of drought duration T and drought deficit V may be described by the lognormal distribution with parameters estimated by the maximum likelihood method. The goodness-of-fit quality was tested by the Anderson-Darling and Cramér-von Mises tests. Both test did not reject the tested distribution neither for any definition nor any cross-section, as the p-values were greater than 15% for the former test and greater than 20% for the latter. ...
For adopted 12 drought definitions and basing on 49-year time series of daily flows at four cross-sections in the Mała Wisła catchment, it was found that the probability distributions of drought duration T and drought deficit V may be described by the two-dimensional lognormal distribution with parameters estimated by the maximum likelihood method. The goodness-of-fit quality was tested by the Anderson-Darling and Cramér-von Mises tests. Both test did not reject the tested distributions neither for any definition nor any cross-section: all of the p-values were greater than 20%. ...
This paper addresses the problem of how drought definition by POT and SPA methods influences drought characteristics. Using the 1984-2013 daily flows at 24 selected gauging stations in the Dunajec river basin and assuming two threshold levels Q70% and Q95% and four minimum drought durations (5, 7, 10 and 14 days) as the pre-set criteria, it was shown that, when compared to the POT method, the application of the SPA method usually leads to less number of droughts and, consequently, of longer duration. The SPA method, differently from POT, reduces dramatically the number of inter-event times, which suggests that some adjacent POT droughts may be dependent and should be pooled. ...
