BIOCLIMATIC CONDITIONS IN MEXICO-CITY - AN ASSESSMENT

Bioclimatic conditions have been assessed for a large urban area locat ed in the tropical highlands of central Mexico using the indices (in d egrees C) of resultant temperature (RT) and effective temperature (ET) . The well-developed heat island effect the city generates, reduces th e number of nights categorized as cold (ET between 5 and 15 degrees C) to cool (ET from 15 to 18.5 degrees 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 effec t 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 da ytime heat island located in these regions, albeit small (urban air te mperature 2-3 degrees C greater than rural), compared with the nocturn al hear island intensity (9-10 degrees C) still adds energy to the alr eady heated afternoon urban air: ET values in the north and central se ctors approach the threshold for comfort (ET of 25 degrees C) during t he 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 d ominating role of temperature in the ET index. Assessment of the diurn al cycle of bioclimatic conditions in downtown Mexico City by means of two empirical indices (effective temperature and thermopreferendum) t hroughout the years gave similar results to those obtained from the ap plication of Fanger's predicted mean vote (PMV) model. An attempt has been made to characterize four bioclimatic zones in the capital city.