Projecting the Frequency of Heat Waves in the 21st Century over the Paris Basin

by Amelia Hamiter

The high mortality of the 2003 heat wave in France, and its particularly severe impact in the Paris basin, has drawn attention to the importance of considering heat wave occurrences of the future. Evaluating heat waves in the Paris region from 1951-2009 and using several climate change and emissions scenarios to model future heat wave possibilities, Lemonsu et al. (2014) predict that the frequency of heat wave occurrences in the target area will increase systematically with time and global warming, and that the durations of these heat waves will grow.

Utilizing the approaches of various climatic studies and the PNC (Plan National Canicule, a national operation warning system set up in the aftermath of the 2003 heat wave), the researchers created a definition of a heat wave that would work with the constraints of climatic projections and took into account public health impacts. The researchers use a reference historical time series to evaluate heat wave occurrences of the past and compare those data with projections of future heat wave frequency. They used daily minimum and maximum air temperature records from various meteorological stations throughout the region, with the longest station records dating from 1945 and the shortest dating from 1974, as well as data from the Météo-France archives, which document main heat wave events in France since 1950. With this data, researchers could extract occurrences observed in the past that they defined as heat waves.

The researchers extracted future heat wave projections using climate and emissions scenarios. Two databases, ARPEGE-Climate-v4 and ENSEMBLES, provided daily minimum and maximum temperature time series from 1950 to 2099, and emission scenarios were applied from 2001. With these time series simulations, projections for different scenarios of future heat waves could be made and compared with past heat waves, allowing researchers to predict the frequency and duration of heat waves over the next century under the various climate and emission scenarios. Similar methods were applied to six other locations in France to ensure the quality of the study methods.

The results of this study stress the need to employ mitigation and adaption strategies to prepare cities for events of extreme heat. The urban heat island effect (the effect/situation of urban environments being subjected to higher temperatures than rural areas) makes taking such actions even more imperative.

Lemonsu, A., Beaulant, A.L., Somot, S., Masson, V., 2014. Evolution of heat wave occurrence over the Paris basin (France) in the 21st Century. Climate Research 61, 75-91.


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