How Reliable Is the Temperature Information of Street Thermometers? A Simple Case Study in São Paulo City

The public information of real time weather in urban places, especially air temperature and humidity, is generally acquired in locus, that is, using local instrumentation, and has also to inform in a convenient and easy way the passerby people, usually displayed in vertical boards of street clocks. These devices seldom use accurate sensors and are placed in vulnerable conditions which include the influence of buildings, trees, wires, vehicles, animals, people etc. This work envisages to discuss how reliable are the temperature data available in the street clocks for passers-by users. We questioned the accuracy of the temperature shown in street thermometers at the USP campus, in Sao Paulo, Brazil. Data was taken during February to April 2014 using an experimental approach that compared the temperature displayed in boards of street clocks/thermometers to a reference air temperature measured in the adjacencies. The board temperature was generally warmer at daytime (mean deviation of 2 °C) in a site not shadowed by surrounding buildings, with extremes that reached about 8 °C, and less in a partially shadowed site. The deviations were larger with clear sky conditions, although the background with diffuse solar radiation was sufficient to show substantial daytime warming. Likewise, at night the board temperature appeared to be colder (mean deviation of about −1.5 oC).