Bordeaux hailstorm of 17th April 2020

June 3, 2020

Saturnalia damage assessment of the hailstorm which struck Bordeaux on April 17

On 17th April, a series of hailstorms struck the Bordeaux area of France, one of the most distinguished regions in the world for fine wine production: here thousands of hectares are covered by vineyards belonging to large wine estates known as “châteaux”.

To be more precise, the first and most severe wave swept over the east part of Bordeaux between 5 and 8pm local time: several media reported that most of the damage occurred in the Côtes de Francs and Entre-Deux-Mers areas; by the time the second wave struck the following day, the hail had subsided and losses were not significant.

Saturnalia continuous monitoring service can help in defining better the area affected by the event through the combination of high-definition satellite images and algorithms. In particular, the Saturnalia Evolution Index computed after the storm shows different possible patterns for the vintages involved in the event.

The chart shows quite clearly the different behaviours in time as registered by the satellites. The green line is an example of a vineyard not affected by the hail: it shows a positive trend, meaning that the vineyard is evolving as it should. On the contrary, the other three lines tell a different story: they tend towards lower values, implying that the plants are not evolving as expected (please take notice that part of the vineyards highlighted as damaged could also be a new implantation; feel free to report us such issues in case you have a direct feedback from the area).

Based on these assumptions, we worked on the areas reported as mostly affected by different articles found online and tried to derive the amount and distribution of the damage.

Côtes de Francs

The first picture shows the distribution of damage in the communes of Puisseguin (blue boundary) and Saint-Cibard (pink boundary), both included in the Côtes de Francs appellation. The three different colours are associated to three classes of damage, as reported in the chart above: red stands for severely affected, orange for mostly affected while yellow for partially affected.

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Figure 2. Hail damage map measured using the Saturnalia Evolution Index in the areas of Puisseguin and Saint-Cibard.

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Figure 3. Map of affected areas released by the Chambre d'Agriculture de la GIronde soon after the event.

As the reader may notice, the red blobs in Figure 2 are quite extended, meaning that large portions of vineyards have been affected by the storm. Saturnalia map can be partially compared with the one produced and released by the Chambre d’Agriculture de la Gironde in Figure 3. The red spots (which are results of in-situ assessment) seem to match quite well the damaged areas highlighted in Figure 2. The comparability is anyway limited, due to the different origin and nature of the datasets: point-wise surveys tend to be accurate but lack coverage, whereas satellite-based maps offer dense coverage but not with the same level of precision as the one deriving from a person on the spot. Still, the two sets appear to largely agree in terms of damage pattern.

Numbers - based on a comparison between the Saturnalia hail damage map and all the vineyards in the area - related to the estimated percentage of hectares of vineyards affected are reported in the pie charts below. Both show a similar percentage of severely affected hectares, with Puisseguin having a total percentage reaching 20% compared to 10% of Saint-Cibard.

Entre-Deux-Mers

Another area severely affected by the April 17 event is Entre-Deux-Mers. The first map shows the extracted damage from the communes of Daignac (blue), Grézillac (pink) and Moulon (white).

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Figure 4. Hail damage map measured using the Saturnalia Evolution Index in the areas of Daignac, Grézillac and Moulon.

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Figure 5. Map of affected areas released by the Chambre d'Agriculture de la Gironde soon after the event.

By visual comparison, the map in Figure 4 shows fewer areas with a behaviour classified as “severely affected”. Again, a quick comparison with Figure 5 seems to confirm our results in terms of distribution of damage. The pie charts below describe the distribution of damage for the three communes considered: the most affected seems to be Daignac.

The second area refers to the communes of Flaujagues (blue), Juillac (pink) and Sainte-Radegonde (white).

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Figure 6. Hail damage map measured using the Saturnalia Evolution Index in the areas of Flaujagues, Juillac and Sainte-Radegonde.

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Figure 7. Map of affected areas released by the Chambre d'Agriculture de la Gironde soon after the event.

Figure 6 and 7 focus again on the hail damage map extracted through the Saturnalia Evolution Index and compared with the report published by the Chambre d’Agriculture. The most severely hit area seems to be Sainte-Radegonde, while Juillac and Flaujagues appear to be much less affected. The charts below allow a better understanding, as they show the damage percentage of the vineyards.

Conclusion

Saturnalia builds on continuous monitoring of vineyards both from space and from ground. We were notified about the hail event that occurred on April 17 and we deployed our Saturnalia Evolution Index to assess the potential damage. We carried out three case studies in two different areas which were reported by media as severely affected: Côtes de Francs and Entre-Deux-Mers. We also compared our results with those published by the Chambre d’Agriculture - based on in-situ inspections - and the patterns look very similar. Our analysis can cover entire communes, like those shown in the case studies above, but can also zoom in to single parcels. As an example, Figure 8 shows a detail of single plots in the Saint-Émilion area that was affected as well. Please feel free to contact us if you are interested in these results, if you want to know more and you would like to get a more detailed report of the most affected vineyards in a specific area.

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Figure 8. Hail damage map - focus on single parcels

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