CDO

Hi Farhan,

I have written - without guarantee - a script that should calculate "specific number of heatwaves days" for the case rhum > 66pctl and rhum < 33pctl.

#!/usr/bin/env ksh

tmpfile="$HOME/Downloads/tmp.nc" 
rhumfile="$HOME/Downloads/rhum.nc" 
tmp90="$HOME/Downloads/tmp90pctl.nc" 
rhum66="$HOME/Downloads/rhum66pctl.nc" 
rhum33="$HOME/Downloads/rhum33pctl.nc" 
heatwave="$HOME/Downloads/heatwave_event.nc" 

#-- delete old files
rm $tmp90  $rhum66 $rhum33 \
   $HOME/Downloads/heatwave_event.nc \
   $HOME/Downloads/heatwave_days_rhum_gt_66pctl.nc \
   $HOME/Downloads/heatwave_days_rhum_gt_33pctl.nc

#-- compute the 90th percentile for eca_hwfi:
#--     TGn90 is calculated as the 90th percentile of daily mean temperatures 
#--        of a five day window centred on each calendar day of a given climate 
#--     reference period
echo "----> compute tmp 90pctl" 
cdo -timpctl,90 $tmpfile  -timselmin,5 $tmpfile -timselmax,5 $tmpfile $tmp90

#-- to get rid of the ERROR: 
#--     cdo    eca_hwfi (Abort): Input streams have different time values!
cdo -add $tmp90 -sub $tmpfile $tmpfile $HOME/Downloads/tmp90pctl_with_timesteps.nc
tmp90="$HOME/Downloads/tmp90pctl_with_timesteps.nc" 

#-- a heatwave event is defined as one in which temperatures exceeded the 
#-- 90th percentile of the daily mean temperature for at least three 
#-- consecutive days, respectively

echo "----> compute heatwave_event.nc" 
cdo eca_hwfi,3 $tmpfile $tmp90 $heatwave

echo "----> compute rhum >66%" 
cdo -timpctl,66 $rhumfile  -timselmin,5 $rhumfile -timselmax,5 $rhumfile \
     $rhum66

echo "----> compute rhum <33%" 
cdo -timpctl,33 $rhumfile  -timselmin,5 $rhumfile -timselmax,5 $rhumfile \
     $rhum33

echo "---->  heatwave n-days where rhum > 66pctl" 
cdo -div $tmpfile -gt $rhumfile $rhum66 $HOME/Downloads/heatwave_days_rhum_gt_66pctl.nc

echo "---->  heatwave n-days where rhum < 33pctl" 
cdo -div $tmpfile -lt $rhumfile $rhum33 $HOME/Downloads/heatwave_days_rhum_lt_33pctl.nc

Dear Karin Meier-Fleischer,

Sorry for my late response and thank you for writing the script. There are some points I need to discuss with you can we communicate through email, does it work for you?

Cheers
Farhan

I prefer to answer questions in the forums so that other users can benefit.

What questions do you have?

Hi Karin Meier-Fleischer,

I have the daily precipitation data (mm) and I want to calculate the annual maxima (block maxima), Is there any cdo command to do this?

Does cdo yearmax in.nc out.nc works?

Regards,
Farhan

The operator yearmax is exactly what you are looking for.

From the CDO documentation https://code.mpimet.mpg.de/projects/cdo/embedded/cdo.pdf#subsection.2.8.25)

YEARSTAT - yearly statistical values

This module computes statistical values over timesteps of the same year. ...

...

yearmax: Yearly maximum
                For every adjacent sequence t_1, ..., t_n of timesteps of the same year it is: o(t, x) = max{i(t′, x), t1 < t′ ≤ tn}
...

Dear Karin,
Thank you for the nice explanation. I would also like to ask if is there any CDO command to calculate monthly maxima using daily precipitation data.
Regards,
Farhan

I recommend to read the documentation because you would have found the needed operator very easy 😉 . In most cases the naming of the operators follows the same pattern, when yearly maximum yearmax is then logically is the monthly maximum monmax 😀 . See https://code.mpimet.mpg.de/projects/cdo/embedded/cdo.pdf

Thank you Karin for the help and support 😀

Dear Karin, 

Based on the codes you provided here, I would like to ask: 

1. Can I compute a heatwave using "eca_hwfi" if my input data is "daily maximum temperature" instead of the default daily mean temperature? Like use the above code but with daily maximum temperature as input.

2. Alternatively, if I use "eca_tx90p," whose input data is the daily maximum temperature, and I do the following:

cdo -timpctl,90 daily_tmax.nc  -timselmin,5 daily_tmax.nc -timselmax,5 daily_tmax.nc tmax_90pctl.nc (90th percentile of daily maximum temperatures of a five-day window centered on each calendar day)

Do I need to add "5" in front of the percentile also (cdo -timpctl,90,5)?

"compute heatwave_event" 
cdo eca_tx90p,3 daily_tmax.nc tmax_90pctl.nc heatwave.nc

Does adding "3" in front of "eca_tx90"  imply I am considering at least three consecutive days? If no, how do I compute for at least three consecutive days in "eca_tx90p"

"eca_tx90p" unit is percent, can this be converted to "number of events"?

3.In the above code "cdo -div $tmpfile -gt $rhumfile $rhum66 $HOME/Downloads/heatwave_days_rhum_gt_66pctl.nc" why did you use "div $tmpfile"?

Thank you so much