In this study, we first compute the annual maximum
(AM) precipitation accumulations from running totals
of 1-, 2-, 3-, 5-, 7-, and 10-day time series for all years
when 3B42RT data were available (2000–13) for each
grid box. Choosing the AM series limits the sample size
but is a required procedure for computing the ARI. The
three-parameter GEV distributions are derived by fitting
the AM series using open source MatLab GEV software
(http://www.mathworks.com/help/toolbox/stats/gevfit.
html), which uses maximum likelihood method to fit
the parameters (Kotz and Nadarajah 2000). The best-fit
GEV curves and thresholds for 2–100-yr ARI are computed
with the derived statistical parameters. As an
example, Fig. 1 shows a sample plot of the PDF curves
and return thresholds for different accumulation days
from a randomly picked single grid point located in the
Cascade Range near the border of the states of Washington
and Oregon. The PDFs of multiday precipitation
accumulation not only shift toward larger values as
compared with that of 1-day accumulation as expected,
but also show much wider spread with longer tails at
high accumulations (Fig. 1a).
In this study, we first compute the annual maximum(AM) precipitation accumulations from running totalsof 1-, 2-, 3-, 5-, 7-, and 10-day time series for all yearswhen 3B42RT data were available (2000–13) for eachgrid box. Choosing the AM series limits the sample sizebut is a required procedure for computing the ARI. Thethree-parameter GEV distributions are derived by fittingthe AM series using open source MatLab GEV software(http://www.mathworks.com/help/toolbox/stats/gevfit.html), which uses maximum likelihood method to fitthe parameters (Kotz and Nadarajah 2000). The best-fitGEV curves and thresholds for 2–100-yr ARI are computedwith the derived statistical parameters. As anexample, Fig. 1 shows a sample plot of the PDF curvesand return thresholds for different accumulation daysfrom a randomly picked single grid point located in theCascade Range near the border of the states of Washingtonand Oregon. The PDFs of multiday precipitationaccumulation not only shift toward larger values ascompared with that of 1-day accumulation as expected,but also show much wider spread with longer tails athigh accumulations (Fig. 1a).
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