Flooding Impacting Many Parts of France
France has been experiencing record rainfall this winter. Last week (the final week of February 2026), the country ended a positively-biblical 40 day streak of consecutive days of rain, defined as an average of at least 1 mm of rain from all observing sites across continental France (about 80% of the size of Texas). The previous record was 32 days in 2023. Further details, for all francophone readers, are available from MétéoFrance. Some interesting highlights: since January 1st, Bordeaux received 321 mm (12.6 inches) of rain; they’d expect a total of 260 mm (10.2 inches) for the entire winter. Toulouse is in a similar situation, having received 203 mm (8.0 inches) so far in 2026 when they’d expect only 139 mm (5.5 inches) for the whole season. Across the country, this registered as the wettest February since 1959 with total accumulation more than twice the normal value.
Satellites are an excellent tool for monitoring not only the short-term weather conditions that lead to flooding, but also the longer-term extent of the floodwaters. The VIIRS Flood Mapping Product (quick guide here) provides one such look. Polar-orbiting satellites like those that host VIIRS are well-suited for flood observations because the higher resolution compared to geostationary enables a more detailed view of the extent of the flooding, while the slowly-evolving nature of floods means that the coarser temporal resolution of the polar-orbiting satellites is still adequate to capture the evolution of flooding events. The identification of floodwaters via satellite is conceptually very simple: surface water can be readily identified via satellite, and surface water in a location where water is not supposed to be implies a flood. There are some more challenging aspects to this, however, as clouds, surface snow, and terrain shadows can create regions of false positives and thus a flood detection algorithm needs to accommodate these and other issues.
Flooding products are available from SSEC’s Real Earth. Here is a link to the VIIRS 5 day composite flood product. This product is available once a day over the continents and selected island regions. The advantage of the 5 day composite is that it can help ameliorate the impact of clouds that would otherwise be in the way. The following animation shows the last two weeks of the VIIRS 5 day composite flood product over the Loire river valley in western France, a region famous for chateaux and vineyards. The colors on this product are representative of the fraction of a pixel that is covered by flooding waters: yellow is more than 40% and red is more than 80%. The rapid jump in the flood extent on the 24th is likely a result of the composite nature of this product with many of the preceding days featuring extensive cloud coverage.
Flood detection can be further enhanced with the inclusion of digital elevation models (DEMs). VIIRS observations can be used to calculate a percentage of a pixel that is covered by water. Assuming that the lowest portions of the pixel will be filled with water first, the higher resolution DEM can be used to downscale the macro-scale flooding information to more finely-detailed flood maps. SSEC is developing an experimental 30 m flood depth product that connects the areal coverage of the satellite to the DEM to produce highly-detailed observations of localized flooding. Here’s a sample image from that product, showing the Garonne and Dordogne rivers just downstream from Bordeaux, another famous winemaking region.
Different satellites can give an even more detailed view. Sentinel 2 is a European polar-orbiting satellite, analogous to the United States’ Landsat mission, designed for small-scale mapping and land classification. Among its bands include true-color red, green, and blue channels at 10 m spatial resolution. The downside of this high resolution is that the imager has a very narrow swath, and thus a given location doesn’t get an overpass every single day and clouds can further limit the number of usable views. An archive of Sentinel multispectral observations is available from the EU Copernicus Browser. Below is a slider that enables comparison between two different Sentinel 2 views of the Loire between Nantes and Angers: one from late January before significant flooding and another from late February when flooding is rampant. You can drag the bar back and forth to see how the environment changes between the two dates. It’s clear where the Loire has escaped its banks, and is especially evident in the middle of the image.
Finally, we can also look at the Normalized Difference Water Index (NDWI). Like its more famous cousin, the Normalized Difference Vegetation Index (NVDI), the NWDI takes the difference between the reflectance observed by two satellite bands and divides that by the sum of those bands. In this case, this is the difference between the green (560 nm) and the near IR (842 nm) bands. Water tends to be positive while vegetation and bare soil tends to be negative. Here is a comparison of the NDWI for the two dates, and here the impact of the flooding is obvious.
Fortunately, the amount of rainfall over France has lessened and waters appear to have started to recede.