Bioclimatic conditions in Mexico City - An assessment

Abstract

Bioclimatic conditions have been assessed for a large urban area located in the tropical highlands of central Mexico using the indices (in °C) of resultant temperature (RT) and effective temperature (ET). The well-developed heat island effect the city generates, reduces the number of nights categorized as cold (ET between 5 and 15°C) to cool (ET from 15 to 18.5°C). Most days fall in the cold to cool range and during the warm season (April to June) the bioclimate of Mexico City is mostly within the neutral (comfort) range. The effect of the nocturnal (to the west) and daytime (to the east of the town) heat island is noticeable in the central and northern sectors. The daytime heat island located in these regions, albeit small (urban air temperature 2-3°C greater than rural), compared with the nocturnal heat island intensity (9-10°C) still adds energy to the already heated afternoon urban air. ET values in the north and central sectors approach the threshold for comfort (ET of 25°C) during the warm months around noon. It is not surprising to find that as the nocturnal heat island has increased over the years (1921-1985) as the city grew, so has the ET for the central district and indicating the dominating role of temperature in the ET index. Assessment of the diurnal cycle of bioclimatic conditions in downtown Mexico City by means of two empirical indices (effective temperature and thermopreferendum) throughout the years gave similar results to those obtained from the application of Fanger's predicted mean vote (PMV) model. An attempt has been made to characterize four bioclimatic zones in the capital city.