Assessing the differential impact of vegetated and built-up areas on heat exposure environment: A case study of Los Angeles

The urban heat island (UHI) effect exacerbates heat stress, energy consumption, and public health challenges in urban environments. Traditional studies often combine vegetated and built-up areas, overlooking their distinct thermal behaviors, and rely on Land Surface Temperature (LST), which does not fully capture the heat exposure perceived by humans. This study addresses these gaps by using 1-m resolution mean radiant temperature (T_mrt) to evaluate heat exposure in Los Angeles, separating vegetated areas (VA) and built-up areas (BA). We developed distinct indicator systems for VA and BA and applied random forest regression, spatial error modeling, and SHapley Additive exPlanations (SHAP) to assess their independent effects on T_mrt. Results indicate that vegetated areas, particularly tree canopies and wetlands, provide significant cooling effects on T_mrt, while impervious surfaces like asphalt roads and bare earth increase heat exposure. In built-up areas, the sky view factor showed the strongest positive correlation with T_mrt, while residential areas demonstrated a negative correlation. The study also highlights the relative importance of variables and nonlinear impacts of indicator thresholds on T_mrt. Notably, increasing albedo in impervious surfaces, a conventional cooling strategy to reduce LST, may elevate perceived heat exposure, challenging its effectiveness. These findings emphasize the need for urban planners to prioritize tree canopy coverage in heat hotspots and develop context-specific strategies that address the nonlinear impacts of urban surfaces on heat exposure. Material selection in built-up areas should carefully consider albedo impacts to balance cooling benefits with potential thermal discomfort, providing actionable insights for sustainable urban design.