To relate fine-scale spatial air-temperature variations in local urban heat islands and urban cool
islands—increases and decreases in outside air temperature—within a large urban-climate
archipelago to variations in land-use and land-cover properties in the Los Angeles Basin, the
research team sought to (a) use fine-resolution meso-urban climate models to identify areas of
urban heat and cool islands, select sites for fixed weather monitoring, and choose routes for
mobile observations; (b) relate observed intraurban temperature variations to land use and land
cover and surface physical properties; and (c) calibrate/validate the climate models. The
research team assessed urban temperature variations via simulations and observations,
including mobile transects, mesonet, dense networks of personal weather stations, and sparse
but more accurate research-grade monitors. To identify the causative factors of the urban heat
and cool islands at the neighborhood scale, the research team collected detailed urban
morphometric and land use and land cover datasets, such as 1-meter (3.3 foot) resolution roof
albedo (solar reflectance) and tree canopy cover. The research team used the observationvalidated model to finalize the transect routes and site the stationary monitors.
This study provides the first observational evidence from analysis of high-spatial-density
weather stations that increases in roof albedo at neighborhood scale are associated with
reductions in near-surface air temperature. This finding was corroborated with the analysis
from mobile transect measurements and correlation of observed air temperature with
neighborhood-scale albedo and vegetation. This correlation revealed a cooling effect from areawide increase in albedo or canopy cover or both.
The calibrated meteorological model accurately identified the localized urban heat and cool
islands observed in this study. Interested stakeholders/researchers can use the same models
and calibration/validation methodology to characterize within-city microclimate variations
elsewhere in California, and can apply them to analyze the benefits from using urban heat
This project report is an extended and more detailed version of a related report prepared for
California’s Fourth Climate Change Assessment.