Fits an extreme value distribution using L-moments to the dry spells of a time series of discharges and subsequently estimates quantiles (the so called T-years event) for given return periods. In the presence of zero flow observations a mixed distribution is fitted.
tyearsS(lfobj, event = 1/probs, probs = 0.01, pooling = NULL,
dist = "wei", check = TRUE, zeta = NULL,
plot = TRUE, col = 1, log = TRUE, legend = TRUE,
rp.axis = "bottom", rp.lab = "Return period", freq.axis = TRUE,
freq.lab = expression(paste("Frequency " *(italic(F)),
" = Non-Exceedance Probability P ",
(italic(X) An object of class 'evfit', see evfit.
An object of class 'lfobj' or an object which can be coerced to class 'xts'. Either with a single column or with a column named 'discharge'.
numeric vector specifying the return periods. E.g. event = 100 will yield the 100 years extreme low flow event.
Alternate way to specify the return period of the event.
a pooling function, see pooling.
A character vector of distributions to fit. Basically all distributions provided by Hosking's lmom-package and their reversed counterparts can be chosen.
logical, should check_distribution get called?
numeric vector of length one for manually setting a lower bound. Only a few distributions allow for a lower bound, namely 'gpa', 'ln3', 'wak' and 'wei'. The default value of NULL results in not bounding the distribution, therefore the parameter zeta is estimated.
logical. If TRUE, sample observations as well as estimated quantile functions are plotted.
numeric or character vector of length one or as long as dist, specifying the colour used for plotting.
logical. If TRUE probabilities will be plotted on a double logarithmic scale.
logical, should a legend be added to the plot?
vector of length one, specifying if and how an additional scale bar for the return periods is drawn. Possible choices are 'bottom', 'top' and 'none'. Alternatively, the position of the scale bar can be specified as an real number between 0 and 1, indicating the y-position of the legend.
character vector, text above the scale bar for return periods
logical, should an additional abscissa showing the probabilities be drawn on top of the plot?
character vector, text above the probability axis
character vector, a label for the x axis
character vector, a label for the y axis
character vector of length one. Either 'v' to calculate volumes or 'd' for durations.
function like max or sum used for aggregating volumes or durations of a hydrological year.
vector of length one, providing the start of the hydrological year. This is evaluated by water_year. The default is, to retrieve the values stored in the attributes of the lfobj.
arguments passed on to find_droughts, e.g. threshold.
Gregor Laaha
This function is vectorised over dist and event.
According to paragraph 7.4.2 of the WNO manual, special care has to be taken in the presence of zero flow observations. A cdf called G(x) is fitted to the non-zero values of the original time series
If a distribution is fitted which allows for finite lower bound (zeta), and zeta is estimated being negative, estimation is repeated constraining zeta = 0. If this behavior is not desired, the parameter zeta has to be set explicitly.
Gustard, A. & Demuth, S. (2009) (Eds) Manual on Low-flow Estimation and Prediction. Operational Hydrology Report No. 50, WNO-No. 1029, 136p.
There are methods for printing summarizing objects of class 'evfit'.
evfit
data("ngaruroro")
rp <- c(1.3, 3, 5, 35)
sumD <- tyearsS(ngaruroro, event = rp, dist = "wei",
variable = "d", aggr = sum)
sumD
summary(sumD)
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