Vulnerability and adaptation of Paris metropolitan area to future heat waves

The VURCA project studies the vulnerability and adaptation of Paris to future heat waves. Through an interdisciplinary team of climatologists, atmospheric physicists, economists and specialists in construction, it was able to develop a framework to analyze prospective effects of different policies aiming at reducing heat waves impacts. A numerical set-up is implemented to simulate the urban climate of Paris in the future (under different scenarios of urban expansion, adaptation measures for buildings, and use air-conditioning) for various heat-wave conditions representative of a large span of possible future events. For each simulation, indicators of heat stress for population and energy consumption for air-conditioning (AC) are produced. The results show that Paris could be strongly affected by heat waves at the end of the century (almost 11 heat-wave days per year in average, according to the analysis of climate projections). In a reference scenario without AC, 7.5 hours per heat-wave day would be spent in average in high heat-stress conditions inside buildings, and 15 hours in the streets. It is also shown that alternative scenario favoring a "compact city" could worsen heat-wave impacts through an increased heat island effect. It is simulated that massive use of AC to insure indoor thermal comfort would lead to more than 1 TWh per year of extra final energy consumption, while degrading the outdoor microclimate because of heat releases. It is also simulated that adaptation policies could be implemented to significantly reduce AC energy demand thanks to massive creation of green spaces in Paris, stricter building insulation rules, and effective recommendations leading to a careful use of AC (with temperature set points higher than 23°C). Finally, it is noted that greening and insulation strategies only do not allow to ensure a quite satisfying comfort, so that it seems difficult not to equip cities with AC in the future.