Future Changes in Extreme Heat Waves in High-resolution Time-slice Simulations

Extreme heat waves have become increasingly dangerous as the climate warms. Twice in the last twenty years, in 2003 and 2010, heat waves causing deaths in the tens of thousands have struck Europe. In summer 2019, a pair of intense heat waves in Europe and another in Alaska shattered numerous records. It is expected that these events will continue to worsen. Not only will the heat become more extreme due to global climate change, as many previous studies have shown, but the distribution of extreme heat waves within a warmer climate may shift, bringing potentially deadly impacts to regions that may be unprepared.

Here we analyze projected changes in heat waves, using output from current and future “time-slice” simulations carried out with a high-resolution (15 km grid scale in the Northern Hemisphere) version of the Model of Predictions Across Scales – Atmosphere (MPAS-A). Ten non-sequential years of observed sea-surface temperatures (SST), chosen to sample a range of ENSO states, are applied as boundary conditions to MPAS-A. Future (end of the 21^st century) simulations are performed by modifying SST with changes taken from a suite of CMIP5 models using the RCP8.5 scenario. The MPAS-A output is used to compute monthly means and standard deviations of surface air temperatures at each model grid point under both climate regimes. Extreme and persistent summertime heat waves are identified as 95^th percentile temperatures lasting a minimum of 3 days. We find a significant westward shift in Eastern Europe heat waves; the greatest frequency of these events shifts from southwestern Russia and northwestern Kazakhstan in the present-day climate into southeastern Europe, Turkey, and Syria in the future. This shift may be a result of the projected drying of the Mediterranean region in the future.