LOS ANGELES’ URBAN HEAT ISLAND CONTINUES TO GROW: URBANIZATION, LAND USE CHANGE INFLUENCES

Abstract

The Los Angeles urban heat island has been recently described as a large, coastal, urban archipelago. Rather than one symmetric UHI, the sprawling metropolitan region can be thought to have several heat islands of differing sizes and magnitudes. Both of these parameters are dynamic, changing over time. The current study focuses on this dynamic nature, showing diurnal, seasonal and spatial aspects to the Los Angeles heat islands. Rather than finding one value for the surface air heat islands, we present the evolving magnitudes based on observational data not models. We also show the significance of the city’s changing land use as a primary cause for the growing heat islands. Using downtown Los Angeles weather data (DTLA), the downtown heat island is defined by the difference between a suburban residential site, an open space site near suburbs and DTLA. Hourly temperature differences are presented for all months and seasons. Another comparison of the downtown heat island is made using the coastal airport (LAX) data. The influences of coastal sea breezes, complex topography, and a climatic rapid warming away from the coast will also be discussed as it hinders evaluating the urbanization inputs. From the two inland sites, there are definite heat island characteristics when compared to the downtown location. DTLA shows continued warming over the 2000-2010 period of nearly 7oC/century for Tmin and 10oC/century for Tmax, which is pretty frightening. The inland sites warm much less during the day and showed a slight cooling for Tmin over the decade. Land use change in the urban Los Angeles County and impervious surface percentages are also calculated for the 1970-2010 period.