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2.7 Time coverage
Period of analysis is 2000-2019; length of monitoring data series varies with minimum length of 5 years.
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Comment from AT
As this is the chapter of the general methodology for the indicator applied in future, it would be good to explain the conditions/principles more in general. E.g the time window covers e.g. the past 20 years.... Is it generally 20 years? Will it me be a moving period of analysis at each point of dissemination? 2002-2021 in 2 years? Or will it expand to more years? 2000-2021?
What about the minimum length of time series? Is it 5 years (too short)? The last 5 years? Is it comparable when you take Site1 (e.g. CY1980-090 ) with values from 2000-2012 and compare it with site2 (e.g. EESJA5507000) with data from 2010-2019? Very unclear, probably very incomparable.
What if the time series of a site of 2000-2019 does not show a trend but the segment of 2015-2019 does show a trend? Which one do you take? Is it up to individual decision to decide which segment is taken?
What about data gaps? How many are acceptable? Is it a concrete number of gaps or a percentage of the time series (e.g. 10%)
Thank you for your comment. Inaccuracies in the description of the methodology are resolved. The approach concerning the minimum data requirements is as follows: The minimum length of measurement series used for the calculation of the GLT is 5 annual records within a 20-year time window (2000 until 2019). Years are not necessarily consecutive. No gap filling was applied.
We agree that 5 years might be too short for thorough evaluation of long-term groundwater level trends. However, the available dataset was very limited. The methodology was developed with the intention to make best use of the capacity of the available groundwater level dataset. In the indicator assessment sheet, a request is made to the countries to submit groundwater level data to the WISE-3 database that for longer periods and with better coverage.
If and when more datasets become available that cover long time periods, the methodology of the GLT indicator can be improved. The suggestions that you provide can be taken up in such an improvement of the methodology.
POLAND
Inaccuracies in the description of the methodology - e.g. in the consulted material at the beginning of the methodology it is as follows: „The minimum length of measurement series used for the calculation of the GLT is 5 years within a 10-year time window, based on the recommendation of the WFD CIS document of quantitative status assessment (CIS, 2009). Years are not necessarily consecutive”, and then in part 2.7 Time coverage: „Period of analysis is 2000-2019; length of monitoring data series varies with minimum length of 5 years”. These two sentences do not have the same meaning.
Thank you for your comment. Inaccuracies in the description of the methodology are resolved. The approach concerning the minimum data requirements is as follows: The minimum length of measurement series used for the calculation of the GLT is 5 annual records within a 20-year time window (2000 until 2019). Years are not necessarily consecutive. No gap filling was applied.