Alternative Implementations of the “Pseudo-Global-Warming” Methodology for Event-Based Simulations

The pseudo-global-warming (PGW) methodology provides an efficient means to investigate the response of a weather or climate event under an imposed climate change signal. In the traditional PGW implementation, this signal is represented through climate-change “deltas” constructed using monthly averages of global climate model (GCM) output over decadal or longer periods during the past and future. The implications of alternative formulations of such deltas were explored herein. Diurnally varying (DV) deltas were compared to the time-constant (TC) deltas used in the traditional PGW implementation; this was done to test the potential effect of future changes in the diurnal cycles of temperature, humidity, and winds. Deltas created using 10-year averages were compared to those using 30-year averages, to examine the effects of the time-averaging period in the delta construction. Finally, the common practice of additionally averaging across multiple GCMs to form a composite delta was also considered. Using simulations of three different historical convective storm events, it was shown that each of these PGW delta formulations results in differences in simulation metrics such as total accumulated rainfall, and convective intensity, but major and/or unambiguous differences were not always found. It is recommended that users of the PGW approach carefully consider all implications of delta formulation on their particular problem.