Aspects of heat-island development in Guadalajara, Mexico

The magnitude of the urban effect on temperature in the tropical city of Guadalajara is examined. Parallel to the city's growth, air temperature shows an increasing trend; over a 40-year period (1931–1970) this rate was of the order of 0.03°C yr⁻¹. As would be expected, this rate of temperature increase has been uneven over the period. When population increase per decade was large (90%), as in the 1940s the corresponding rate was significant (0.4°C per decade). The largest warming rate (0.7°C per decade) occurred during the 1960s when population growth was 73%. These results suggest that other factors (on a regional/global scale) may have been at play. Results show that estimates of the intensity of the heat island in a tropical city are likely to be dependent (besides the physical factors implicit in the city size), on the land-use characteristics in the rural/suburban control. Since the suburban/rural substrates undergo a significant annual variation in their physical properties in Guadalajara, heat-island intensity is highest during the dry season and declining in the wet season when contrasts in urban/rural thermal admittance are likely to be minimal. The presence of lower temperatures in the city during the afternoon hours suggests that the city (especially in the dry season) acts as a moisture source. This “cool” island has also been observed in other cities with similar regional climate.