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Activate the hydrology menu. The following options are available: Hydrology Menu
Hydrograph
Analyze partial duration series
Hydrograph
The hydrograph option is applicable to Xtremes Time Series.
It is a special construction of a scatterplot
employed in flood frequency analysis. Local thresholds are introduced to
detect a clustering and to select floods and droughts.
Notice that the hydrograph is not explained
in Statistical Analysis (yet see Demo 11.1).
To reduce the huge number of, e.g.,
daily measurements y[i] of discharges or water levels at time i,
certain upward and downward peaks are selected. The
approach to this question is guided by the method of building clusters by
runs.
First, we deal with the selection of upward peaks.
Three parameters must be selected, namely
The default parameters are c = 0.25 and r(0) = r(1) = 1.
Increase these parameters to reduce the amount of information
inherent in the hydrograph. Details:
Likewise, downward peaks are selected for the same parameters
out of downward clusters with respect to
thresholds u[i] = (1+c)y[i]. Finally, the upward and downward
peaks are combined and plotted.
Analyze partial duration series
Flood peaks, given as an Xtremes Time Series,
are dealt with under the assumption that the frequencies
of occurrence and the magnitudes only exhibit a seasonal dependency.
The option Analyze partial duration series is applicable
if the modeling by an inhomogeneous Poisson process with independent
marks is adequate.
Therefore, it can be necessary to decluster the data
(also see Demo 11.3) in a first step. For that purpose use the
option
Save Cluster Maxima
to get independent cluster maxima over a certain threshold. Visualize
the resulting time series
in a
Scatterplot.
Executing Analyze partial duration series one enters a
dialog box where several parameters must be specified:
Pressing OK one gets a scatterplot of the data (modulo 365),
a plot of weekly frequencies,
the T-year values u(T) (read the pages 265-267
in Statistical Analysis) plotted against T, and
an active data set called pardur.dat. For each day where parameters
were evaluated, the shape and scale parameters of the
estimated generalized Pareto distributions are stored in pardur.dat
(the values are put equal zero, otherwise). Visualize the parameters
by means of scatterplots!
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