Simulating the Efficacy of Targeted Urban Heat Mitigation for Vulnerable Populations

Excessive summertime heat is a pressing problem for many cities. Fortunately, there are several mitigation alternatives that show promise for cooling urban climates (e.g., high albedo surfaces and increased vegetative cover). The high cost of city-wide implementation of such strategies, however, provides motivation for a more targeted approach. In many cities one can identify regions that are relative hot spots in terms of summertime air temperatures. Likewise, it is possible to identify regions with particularly vulnerable populations--disproportionately poor and elderly, and those without access to air conditioning. In this study we look at this intersection between hot spots and vulnerable populations to explore the potential benefits of targeted mitigation at the neighborhood scale—in terms of both ambient and indoor thermal conditions.

As a case study we focus on one such neighborhood in Los Angeles. We use the ENVI-met microscale atmospheric modeling tool to assess the footprint effects of limited-area urban heat mitigation strategies, including both roof-level and ground-level albedo enhancement. Results for near-surface ambient air temperature perturbations are presented. These results are then used to drive building indoor thermal environment simulations with EnergyPlus to explore potential for targeted urban heat mitigation to improve indoor conditions during heat waves. Also, recognizing inherent modeling limitations associated with the user-friendly nature of ENVI-met, we conducted sensitivity tests and compare ENVI-met performance to results from a more sophisticated Computational Fluid Dynamics tool (Star-CCM+) for a range of neighborhood configurations and implementations of mitigation strategies. From these comparisons we conclude that ENVI-met must be used with caution for exploring roof-level heat mitigation strategies, particularly for multi-story buildings.