Heat island development in Mexico City

The present paper describes the climatology of the near surface urban heat island of Mexico City, using hourly data from two recently installed automatic stations at a rural and an urban site. The results show that the nocturnal heat island was more frequent (75% of the time for the period examined) than daytime cases (25%). The maximum nocturnal heat island intensity, 7.8 degrees C was observed in a dry month (February) characterized by calm clear nights. Although less frequent, the daytime heat islands did occur and may have been caused by differences in evaporative cooling from wet surface during the wet season. Midday heat islands had a frequency of 13% and an intensity of 3-5 degrees C during the wet season. The afternoon/evening heat islands had an intensity of 4-5 degrees C. They occurred during both dry and wet season with a frequency of 12% of the time in a year. The average urban/rural thermal contrasts are positive throughout the year varying from 5 degrees C at day break in the middle of the dry season to 1-3 degrees C around noon during the wet months. (C) 1997 Elsevier Science Ltd.