Study of the future evolution of the urban climate of Paris by statistical-dynamical downscaling of the EURO-CORDEX ensemble

Abstract

High-resolution urban climate projections are needed for local decision-making on climate change adaptation. Regional climate models have resolutions that are too coarse to simulate the urban climate at such resolutions. A novel statistical-dynamical downscaling approach (SDD) is used here to downscale the EURO-CORDEX ensemble to a resolution of 1 km while adding the effect of the city of Paris (France) on air temperature. The downscaled atmospheric fields are then used to drive the Town Energy Balance urban canopy model to produce high-resolution temperature maps over the period 1970-2099, while maintaining the city’s land cover in its present state. The different steps of the SDD are evaluated for the summer season. The regional climate models simulate minimum(maximum) temperatures (TN/TX) that are too high(low). After correction and downscaling, the urban simulations inherit some of these biases, but give satisfactory results for summer urban heat islands (UHI), with average biases of −0.6 K at night and +0.3 K during the day. Changes in future summer temperatures are then studied for two greenhouse gas emission scenarios, RCP4.5 and RCP8.5. Outside the city, the simulations project average increases of 4.1 K and 4.8 K for TN and TX for RCP8.5. In the city, warming is lower, resulting in a decrease in UHIs of −0.19 K at night (from 2.1 K to 1.9 K) and −0.16 K during the day. The changes in UHIs are explained by higher rates of warming in rural temperatures due to lower summer precipitation and soil water content, and are partially offset by increased ground heat storage in the city.