Modeling Future Heat Extremes in Milwaukee Wisconsin Using Extremes-Preserving Psuedo-Global Warming Methods
Image credit: AGUAbstract
Heatwaves are one of the deadliest natural hazards, and are projected to intensify by the end of the century due to anthropogenic climate change. Urban areas are especially at risk due to high population densities and high temperatures that result from land-atmospheric interactions like urban heat islands. One way to analyze potential changes in heatwaves and other hydrometeorological extremes is to use Pseudo-Global Warming (PGW) methods. Traditional PGW methods translate projections from Global Climate Models (GCMs)/Earth System Models (ESMs) into local/regional predictions by first finding changes (known as “deltas”) in 3D thermodynamic and dynamic variables (e.g. temperature, humidity, winds, and geopotential heights) and changes in surface variables (surface radiative temperatures, 2m air temperatures, 2m humidity, etc.) between a future and a reference period. Then, these deltas are used to perturb historical weather events in order resolve potential changes high impact events that could occur due to climate change. While insightful for mean conditions, when examining high impact hydrometeorological events like heatwaves, changes in mean conditions may not be representative of the conditions that lead to these events and that will intensify them in the future. In this study, we compare different PGW methods in Milwaukee, Wisconsin using a high resolution regional climate model. We use both the traditional PGW and a new quantile mapping approach that leverages CMIP6 large ensembles to identify deltas that are consistent with the exceedance probabilities of the historical heatwaves. Then, to investigate the inherent uncertainty in both current and future conditions, we generate ensembles to evaluate urban heat and changes in sensible and latent heat partitioning within the Milwaukee region. Our findings highlight the necessity of considering event-specific atmospheric condition changes, e.g. specific quantiles, when evaluating hydrometeorological extremes like heatwaves in the context of climate change.
