Assessing Urban heat resilience in the Portland metropolitan area: Built environment associations with late-day resistance and evening-to-morning recovery cooling

Persistent late-day and nighttime heat pose health risks, yet urban heat assessments often rely on peak or single-time measures, obscuring how heat burden changes across daily measurement periods. Using modeled near-surface air-temperature surfaces from the 2023 CAPA-NIHHIS Heat Watch campaign in Portland, we assessed afternoon, early-evening, and same-day morning-reference air temperatures across 200 m neighborhood typologies and census block groups. We operationalized heat resilience through two interval-based measures: resistance cooling (afternoon to early evening) and recovery cooling (early evening to morning reference), and estimated cumulative air-temperature exposure over 15 h. Built-environment typologies differed significantly in afternoon temperature, evening temperature, resistance cooling, and recovery cooling. Highly impervious and built-up typologies exhibited higher afternoon and evening temperatures, while low-impervious and high-canopy typologies were cooler. Low Impervious High Canopy neighborhoods showed the greatest resistance cooling (3.5 °F), whereas recovery cooling was highest in Low Impervious Low Building and Moderate-Density Residential neighborhoods. Smaller recovery cooling in high-canopy areas should not be interpreted as poorer thermal performance because they maintained lower absolute temperatures. In the case-study comparison, the High Impervious High Building neighborhood accumulated 35.5 °F·h more exposure than the Low Impervious High Canopy neighborhood and 22.7 °F·h more than the Moderate-Density Residential neighborhood. Spatial error models showed higher income was associated with lower afternoon/evening air temperatures, while larger non-White population shares were associated with reduced recovery cooling after physical controls. These findings support phase-specific and equity-oriented heat resilience planning that considers absolute temperature, interval-based cooling, cumulative exposure, and canopy preservation.