Projection of Future Heat Waves in the United States Based on Locally Selected GCMs

Global temperature is rising at an alarming rate and this warming will bring more frequent and severe heat waves. Studies in the United States indicated spatial and temporal variations in the heat wave occurrence within the next 8 decades. This will challenge the general adaption and mitigation plans and focuses on more local preparedness actions. In the absence of Regional Climate Models (RCM) in many locations, downscaled General Circulation Models (GCMs) are the only reliable resources for future weather predictions. However, the variation in the outputs of the GCMs creates many doubts on the robustness of impact studies. Here, 32 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) are examined to determine how well this generation of general circulation models represents the heat wave main components across the United States during 1950-2005. We applied a multi-criteria decision-making tool and ranked the GCMs based on their capabilities in simulating historical heat waves. We found that ec-earth, mpi-esm-lr, canesm2, cmcc-cm, and gfdl-esm2m models show significantly better and fgoals-g2, gfdl-esm2g, hadgem2-cc, access1-0, and inmcm4 GCMs indicate the poorest performances. Then we examined the future heat wave properties and demonstrated that heat wave components could increase, start earlier, or last longer during the next 8 decades even under RCP4.5 path and based on optimistic GCMs. Particularly, we found that the frequency of heat waves could increase to the point that the events are continuous, creating a "heat wave season". In addition, we observed that although nighttime intensity remains significantly higher than daytime intensity, their overall increase will be similar. These findings are aimed to improve impact studies by providing more robust and reliable local weather predictions.