# [ncl-talk] extreme value analysis

Sri.durgesh Nandini-Weiss sri.durgesh.nandini-weiss at uni-hamburg.de
Thu Dec 12 07:12:55 MST 2019

Hello everyone

I tried calculating and plotting extreme value analysis on my SSH data,
following ncl example extval_6.ncl
<https://www.ncl.ucar.edu/Applications/Scripts/extval_6.ncl>:

My plot was generated with no error, but it doe not look correct.

See attached, as well as my script. Can someone advice me? I am happy to
send my data as well.

Sri

;************************************************
; extvalv_6.ncl

hist_anom    = f->hist_anom
printVarSummary(hist_anom)

dimx = dimsizes(hist_anom)
ntim = dimx(0)           ; 240
nens = dimx(1)           ; 100
nlat = dimx(2)           ; 45
nlon = dimx(3)           ; 90
lat1=nlat
lon1=nlon
nmos = 12
nyrs   = ntim/nmos       ; 20
printVarSummary(nyrs)

;==================================================================
; print ("Data read in - start calculations")
; Region domain lat and lon
;==================================================================

hist_anom1=hist_anom(:,:,{48},{-125})               ;(ntim, mlon)
printVarSummary(hist_anom1)
;=================================================================
; extract data between 95-100percentiles
;=================================================================

anom1_1d = ndtooned(hist_anom1)
printVarSummary(anom1_1d)

anom1_nomiss=anom1_1d(ind(anom1_1d.ne.-9999))
anom1_permsort = dim_pqsort(anom1_nomiss,2)
x95=anom1_nomiss(floattoint(0.95*dimsizes(anom1_nomiss)))
i95  =  ind(anom1_nomiss.ge.x95)
xHigh = anom1_nomiss(i95)                 ; values
printVarSummary(xHigh)

;***************************************************************
;---GEV parameter estimation
;***************************************************************

vals     = extval_mlegev (xHigh, 0, False)    ; dims=0
print(vals)

center   = vals(0)                            ; extract for clarity
scale    = vals(1)
shape    = vals(2)
;ptype=0
pdfcdf   = extval_gev(xHigh, shape, scale, center,0)
;pdfcdf = extval_pareto(xHigh, shape, scale, center, ptype, 0)   ;
[/ PDF, CDF /]
pdf      = pdfcdf[0]                          ; extract from list
for convenience
cdf      = pdfcdf[1]
delete(pdfcdf)

printVarSummary(pdf)
printMinMax(pdf,1)
print("---")
printVarSummary(cdf)
printMinMax(cdf,1)
print("---")

;***************************************************************
;--- PLOTS
;***************************************************************

plotfile="Hist_SSH"
wks_type = "pdf"
wks = gsn_open_wks(wks_type,plotfile)

gsn_define_colormap(wks,"default")
plot = new(2, "graphic")
res     = True
res at gsnDraw  = False
res at gsnFrame = False
res at tiYAxisString = ""

it      = dim_pqsort_n(xHigh, 1, 0)        ; for plot reasons make
'x' is asebding

;************************************************
; Panel
;************************************************

resP                     = True                  ; modify the panel plot
resP at gsnMaximize         = True                  ; ps, eps, pdf
resP at gsnPanelMainString  = "River Flow Rate"     ; use this for NCL
V6.4.0 and later
resP at txFontHeightF       = 0.020

;************************************************
;--- Plot PDF and CDF ; create panel
;************************************************

plot(0) = gsn_csm_xy (wks,xHigh(it),pdf(it),res) ; create plot

res at trYMinF  = 0.0
res at trYMaxF  = 1.0

plot(1) = gsn_csm_xy (wks,xHigh(it),cdf(it),res) ; create plot

gsn_panel(wks,plot,(/1,2/), resP)             ; now draw as one plot

--
Dr. Sri Nandini-Weiß
Research Scientist

Universität Hamburg
Center for Earth System Research and Sustainability (CEN)
Cluster of Excellence 'Climate, Climatic Change, and Society' (CLICCS)

Bundesstrasse 53, 20146 Hamburg
Tel: +49 (0) 40 42838 7472

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