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The application automatically updates its data in the month following the end of the required season. For the JFM temperature, this is on day 30 of April. For the JJA precipitation it is on day 30 of September.

Application interface

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The map’s graphical display contains four visible layers, applicable to both variables:

• Mean temperature (Jan-Feb-Mar)/ Total precipitation (Jun-Jul-Aug) – the default map selection - displays the variable from the dropdown menu for the selected year in the time slider.
• Threshold (10^th percentile) – displays the 10^th percentile value for each Member State Proximity to threshold  – shows for each year the difference between the variable and the threshold. This layer displays how far each Member State is from the threshold value for the selected year in the time slider.
• Below threshold – a binary display showing the Member States falling below the threshold for the selected year in the time slider .Proximity to threshold  – shows for each year the difference between the variable and the threshold. This layer displays how far each Member State is from the threshold value (Figure 2).
• Threshold (10^th percentile) – displays the 10^th percentile value for each Member State for the selected year in the time slider. The 10th percentile means that the winter (JFM) / summer (JJA) belongs to the 10% coldest / driest using the 30-years reference period 1991-2020 obtained from ERA5 monthly and then seasonally averaged data
• Mean temperature (Jan-Feb-Mar)/ Total precipitation (Jun-Jul-Aug) – the default map selection - displays the variable from the dropdown menu for the selected year in the time slider (Figure 1).

The data value is presented upon hovering the mouse over the Member States.

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Clicking on a Member State in the interactive map will open a detailed view for that Member State and present a timeseries graph – line- or bar-graph depending on the variable selected (e.g. Figure 13, right panel). The graph presents the values calculated for each year together with the threshold identified by the 10th 10^th percentile (red line). The exceptionally cold winters dry summers are identified by the red data points and are bars situated below the threshold line.

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• Step 1: Retrieve the monthly mean temperature data for January, February, and March (JFM) over Europe (area:  34-72N; -25-45E) for each year between 1991 to present from the CDS catalogue entry.
• Step 2: Calculate the average temperature over the three months for each year, for each grid point (temporal dimension).
• Step 3: Calculate the Member State median JFM temperature for each year using the data from step 2 above (spatial dimension).
• Step 4: Estimate the 10th 10^th percentile over the reference period (1991-2020) for each year and for each Member State.
• Step 5: Identify the years that fall below the 10^th percentile estimated in step 4 and mark them as below the threshold years.

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• Step 1: Retrieve the monthly mean precipitation data for June, July, and August (JJA) over Europe (area:  34-72N; -25-45E) for each year between 1991-present from the CDS catalogue entry.
• Step 2: Calculate the sum of the precipitation over JJA for each year for each grid point (temporal dimension).
• Step 3: Calculate the Member State median JJA precipitation for each year using the data from step 2 above (spatial dimension).
• Step 4: Estimate the 10th 10^th percentile over the reference period (1991-2020) for each year and for each Member State.
• Step 5: Identify the years that fall below the 10^th percentile estimated in step 4 and mark them as below the threshold years.

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1. https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=uriserv%3AOJ.L_.2016.344.01.0001.01.ENG
2. https://cds.climate.copernicus.eu/cdsapp#!/dataset/reanalysis-era5-single-levels-monthly-means