Defintion of growing season length in eca_gsl differs from the one used by ECA

Added by Stefan Fronzek over 14 years ago

Dear colleagues,

the website of the European Climate Assessment (ECA) gives a definition of the growing season length (GSL) at http://eca.knmi.nl/images/indices/GSL.png. There, the start of the growing season is defined to be the 1st occurrence of at least 6 consecutive days with TG > 5oC.

This definition differs from the one implemented in cdo (https://code.zmaw.de/embedded/cdo/1.4.5/cdo.html#x1-6530002.16.9), where the start of the growing season is restricted to be within the first 6 months of the year.

cdo gives a missing value for the growing season length for a time series of TG that exceeds 5oC only after the end of June, whereas with the ECA definition the growing season could be several weeks in July and August. Such a situation is quite often the case in higher latitudes or altitudes.

I am struggling how to best deal with these missing values when calculating GSL for northern Europe and would prefer a definition of the start of the growing season that is not restricted to the first 6 months.

What is the reason why GSL is apparently defined differently in cdo? Since the climate indices' names in cdo all start with "eca_", I assumed they would be implementing exactly what has been done by ECA.

Best regards,
Stefan

Replies (5)

RE: Defintion of growing season length in eca_gsl differs from the one used by ECA - Added by Ralf Mueller over 14 years ago

Hi Stefan,
thanks for the hint. Unfortunately I did not used the official definition for rechecking the implementation. Instead I added support for southern hemisphere, where the end lies in the first 6 month of the year. I created an issue (#396) for your report.

To compute the correct GSL, you should propably use the consecsum operator. It has been developed to gain deeper insight into periods of consecutive timesteps. See #14 for usage help. Here is a little workflow for manually computing the GSL beginning:

Mask the data for temperatures above 5oC, e.g. with
```
cdo gtc,5 inFile maskFile
```
for the start of the period.
Compute the lenght of each period of consecutive timesteps with value 1:
```
cdo consecsum maskFile periodsFile
```
Check for the first timestep with value 6:
```
cdo eqc,6 periodsFile startOfGSLFile
```

regards
ralf

RE: Defintion of growing season length in eca_gsl differs from the one used by ECA - Added by Stefan Fronzek over 14 years ago

Hi Ralf,

thanks for pointing to these operators. I couldn't find a way in cdo to check for first timestep where a conditions is met (i.e. the first occurrence of 1 in the above file startOfGSLFile). Is there such an operator?

regards,
Stefan

RE: Defintion of growing season length in eca_gsl differs from the one used by ECA - Added by Ralf Mueller over 14 years ago

Hi Stefan,
such an operator would produce a file with grids and time axes similar to the input file; data would be a single '1' at the corresponding timestep and missval otherwise. Is that, what you intend?

Could I send you a patched cdo tar ball for checking the eca_gsl operator?

regards
ralf

RE: Defintion of growing season length in eca_gsl differs from the one used by ECA - Added by Stefan Fronzek over 14 years ago

Hello Ralf,

I would want an output similar to the output from eca_gsl with a single time step that holds the growing season length and the day number of growing season start.

What would be included in the patch that you offered to send? I would be very keen on getting that, if you managed to implement a version of eca_gsl that calculates the growing season start without restricting it to the first 6 months.

Thanks for your help,
Stefan

RE: Defintion of growing season length in eca_gsl differs from the one used by ECA - Added by Ralf Mueller over 14 years ago

Stefan Fronzek wrote:

Hello Ralf,

I would want an output similar to the output from eca_gsl with a single time step that holds the growing season length and the day number of growing season start.

That's allready there. eca_gsl computes 2 variables: growing season lenght and growing season start (day of the year)

What would be included in the patch that you offered to send? I would be very keen on getting that, if you managed to implement a version of eca_gsl that calculates the growing season start without restricting it to the first 6 months.

I'd like to send you a complete tar file, which you can compile an install just like the regular release.

Further work will be logged to #396.

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