Resumen
In this paper the urban heat islands (UHI), both atmospheric and surface, and their relationship with the land use in the city of Mexicali, Baja California, México, were examined by means of direct in situ measurements of air temperature, and the use of NOAÁs AVHRR and Ladsat thermal satellite images. The results show the development of a nocturnal urban heat island, whose highest mean value was recorded in autumn (4.5 ºC), however during the day-time, in any season of the year, this situation is reversed and the city becomes a cold urban island. The existence of a surface urban heat island (SUHI) could be proved when the city was compared with nearby surroundings. Within the city, important thermal contrasts can be seen as a topographic map, and then can be related to different urban land use. The discussion is focused to the relationship that exists between the canopy air temperature, the surface temperature, and the atmospheric energy balance near the ground.