Implementation of the “pseudo-global warming” methodology to understand extreme tornado events under future climate change: Initial results for the May 20, 2013 tornado outbreak

Abstract:

This study aspires to determine how modern extreme tornado events may unfold under future anthropogenic climate change using the “pseudo global warming” (PGW) methodology. To properly apply this methodology, current-day extreme tornado events must be adequately simulated, and then simulated again with a climate-change difference (or delta) applied to the original 3D meteorological forcing. Given its classic supercellular nature and great societal impact, the May 20, 2013 EF-5 tornado that struck Moore, Oklahoma was chosen to be modeled. North American Mesoscale Forecast Model (NAM) data were ingested into WRF-ARW 4.0 to produce a simulation across the parent domain of the southern plains, a nested domain over central Oklahoma, and a further nested domain within. The domains had horizontal grid spacings of 3 km, 1 km, and 0.33 km, respectively. Once deemed representative of the event, the control simulation was compared to simulations with climate-change deltas applied in an attempt to simulate the event in a future environment. These climate change deltas are the differences in future and historical general circulation model (GCM) output. Constructed by subtracting historical (1990-1999) May data from future (2090-2099) May data, the deltas consist of temperature, moisture, wind, surface pressure, and soil differences from 3 CMIP5 GCMs. Differences between future and historical environments were calculated in 3-hour intervals and applied to the NAM input data used in the control simulation. Climate-change deltas constructed only from May days exhibiting CAPE values within various percentiles were also explored in this study. The results of the PGW comparisons will be described, as will the next steps in this study.