Existing Climate Data Sources and Their Use in Heat Island Research

This is an analysis to explore the use of the climate data sources described above in examining the area near Los Angeles, California. This region was selected because previous and ongoing research by our group has focused on the changing urban climate of this area and its effect on energy use and air quality.

Several studies have established the rising temperature trends in the Los Angeles region. Cayan and Douglas (1984) analyzed records of near-surface temperatures at Los Angeles Civic Center as part of a study of urban influences on temperatures in several southwestern cities. The authors found that annual mean temperatures rose with a linear trend rate of 0.03K (0.054°F) per year (1.4K or 2.6°F total) between 1932 and 1980. The temperature rise was more pronounced in summer months, as linear trends for monthly mean temperatures rose over the same period by 0.7K (1.2°F) in January and by 2.3K (4.1°F) in July. They also compared monthly mean maximum and minimum temperatures averaged over the period 1941 - 1970 with those averaged over 1969 - 1980. The increase in mean temperatures in January was largely due to an increase in minimum temperatures, while the increase in July seemed to be caused by rises in both maximum and minimum temperatures.

The same temperature record was examined by Akbari et al. (1990) in a work focusing on energy and air pollution costs of heat islands and the potential for heat island mitigation. Yearly highs between 1880 and 1985 decreased from an average of 38.3°C to 37.2°C (101°F to 99°F) between 1880 and 1930. Thereafter, yearly highs rose to 41.1K (106°F) by 1985, an average increase of 0.07K (0.13°F) per year. Temperature increases were also apparent in monthly average temperatures during the summer months, as shown in Table 3.

Both analyses rely solely on the climate record at the Civic Center and thus are susceptible to bias caused by natural temperature trends, changes in documented station location and elevation, and undocumented sources of bias. In fact, the Civic Center station has been located on various rooftops at different heights in the center of downtown Los Angeles, where microclimate conditions have changed dramatically during the period of record as the area became increasingly dense with tall buildings and busy streets. The station maybe thus inappropriate for historical heat island analysis. In order to establish more confidently the presence of increasing temperature trends in the Los Angeles region, we have undertaken a more complete analysis of Summary of Day data.

Station selection

Figure 1: Elevation contour map of Los Angeles area with locations of the cooperative network stations examined. Contours represent changes in elevation of 350 meters.

A commercially available NCDC Summary of Day station inventory was searched for currently operating stations within the Los Angeles area with data beginning before 1950. Eleven stations were selected, shown on a map in Figure 1 and described in Table 4. The stations at Burbank, Culver City, and the Civic Center are all located in densely built sections of the Los Angeles Basin. The stations in Santa Ana and Tustin/Irvine are located in less dense areas of Orange County. The surroundings of Pomona and Pasadena are also less densely built than those areas in the city center. The stations at Santa Monica and Los Angeles International Airport are located in close proximity to the coast and are strongly influenced by coastal breezes and fog. Torrance is located 5 km from the coast and is also influenced by coastal breezes and fog. Continue to: Chapter IIC. Historical Analysis of the Urban Climate of Los Angeles: Analysis and results