Potential for climate equity: Integrating nocturnal drainage winds into heat mitigation strategies in Portland

Abstract

Limited adaptation options and local-scale heat mitigation measures to counter elevated nighttime temperatures have increased the need for effective and equitable city-scale cooling measures. I proposed that cold and dense air from surrounding high landscapes, called drainage winds, could be a potential city-scale nocturnal heat mitigation measure. I further suggest that this measure can moderate spatial disparities in heat mitigation capacity due to the unequal distribution of urban trees in Portland, Oregon. First, I conducted KLAM_21 wind simulations using grid cells of 30 m with elevation and historical and recent land use types. Then, I used census block groups including the proportion of tree canopy area, socioeconomic variables, and simulated wind attributes in statistical analysis. I found: (1) KLAM_21 simulation results generally align with actual wind observations, (2) urban development over the last two decades lowered the cold air layer, and (3) marginalized neighborhoods with less tree canopy coverage experience greater nocturnal cooling effects from drainage winds. These results emphasize the potential of drainage winds as an equitable heat mitigation option in Portland. Urban planners should integrate scenario-based simulated wind data into heat mitigation strategies to foster a more equitable and comfortable nighttime thermal environment in the long term.