French Riviera flooding raises questions about climate change

Was the heavy rainfall this weekend that flooded the French Riviera and killed 19 people a result of global warming? The rains dumped a month’s worth of water in the space of a few hours. As France prepares to host the COP 21 UN Climate Conference in December, it could be tempting to blame the rains on climate change. But scientists warn about making too direct a connection.

A street in Cannes destroyed by flooding Reuters/Eric Gaillard

Philippe Drobinski is a climatologist, and the coordinator HyMex, which tracks the climate in the Mediterranean:

RFI: Can we say this flooding is due to climate change?

Philippe Drobinski: It is difficult to attribute the meteorological event to climate change. 

I would say that all the ingredients that trigger these types of events are natural, and part of the climate of the region. In this area you have the Mediterranean Sea, which is a source of moisture. At this time of the year you often find cut-off flow off the Iberian Peninsula. And there are mountains. So all the ingredients are here to trigger these types of events. 

It’s very common to have this type of event in the north-western Mediterranean. Last year Genoa was completely flooded with a number of casualties.

Now, in the context of climate change, these events are expected to become more frequent and more intense in the future.

RFI: Why is that the case?

PD: It can be understood physically by the fact that as the atmosphere is warming, its ability to keep more moisture increases: the atmosphere will be able to store more water vapour, so when clouds form, they form with more water, so when precipitation occurs, more water falls to the ground.

RFI: So that explains why a month’s worth of rain falls in one day, as we saw in Southern France?

PD: Once again, this is one event. But for sure, the amount of water that will fall in the future, in the next decades, is predicted to increase as the temperatures warm.

Though now, if we look at the data we have, for the moment we are not able to show, statistically and with a high level of significance, that there is a trend.

For temperatures, the situation is slightly different. We are able to delineate the climate change trends from natural variability.

This is not the case for the moment for precipitation. We don’t have enough high quality data for the moment, but we have digital models that allow us to project the climate in the future, and these models show an increased frequency and intensification of these types of events.

RFI: Talk about the impact of where the rain fell this weekend:

PD: What makes the emotion so strong is the vulnerability of the communities. Urbanization and river management can contribute to increase risk: when you have hazards combined with the vulnerabilities.

Here we are between the two: We have very large cities, Cannes and Nice. So this is a problem that is not only due to the hazard itself, but the vulnerability of the cities that faced this high level of precipitation.