Resumo

MENDEZ-PEREZ, Irving Rafael; TEJEDA-MARTINEZ, Adalberto; LINO-SOLANO, José Juan  e  RIVERO BLANCO, Carlos Octavio. Validity of urban heat island detection through walkthroughs: two examples in eastern Mexico. Invest. Geog [online]. 2023, n.112, e60729.  Epub 22-Abr-2024. ISSN 2448-7279.  https://doi.org/10.14350/rig.60729.

One century after the first drive tour to detect the effects of urbanization on the local climate (Vienna, Austria, 1927; Karlsruhe, Germany, 1929), the method is still valid, as evidenced by recent research mentioned throughout this article. This method was applied in two data recording campaigns in eastern Mexico: June to September 2012 in a coastal city (Coatzacoalcos, 320 thousand inhabitants) and August to November 2018 in a mountainous site (Emiliano Zapata, 20 thousand inhabitants). In both campaigns, the urban heat island (ICU, for its acronym in Spanish) was detected within the urban canopy, whose intensity depended on the type of surface and the dominant atmospheric circulation systems at the time of data recording. The peak ICU intensity at the coastal site is 8.7 °C in the daytime and 3 °C at night, while it is up to 1.9 °C at the mountainous site.

The tours included the urban area and its periphery, with temperature recorded at points representative of the different surfaces or land uses. Gasoline motor vehicles were used. The data recording equipment was calibrated before the campaigns and installed as far away from the engine as possible to avoid data biased by the heat emitted by the engine. Sensors were set to record data at 1-minute intervals. At each recording point, a 10-minute waiting time was allowed to stabilize sensors; then, the temperature corresponding to minute 10 was recorded. We used a HOBO U10-003 data logger in Coatzacoalcos and a Kestrel 4500 portable meteorological station in Emiliano Zapata.

Data were recorded outside of the hours when minimum and maximum temperatures occur because around them it is impossible to identify a clear trend to nighttime or evening cooling or morning warming - a trend necessary to know to reproduce simultaneous thermal measurements.

In both sites, the temperatures recorded were corrected according to the thermal trend during tours and altitudinal differences between recording points.

Eighteen and ten tours were driven for coastal and mountainous sites, respectively. Various weather conditions were considered, for example, clear or partly cloudy skies prior to a cold front or a tropical wave.

From the results, it is inferred that the type of surface, the meteorological events during data recording, and the size of the urban area are key factors determining ICU intensity.

At the coastal site, an anticyclone seems to promote the development of the ICU, except for significant meteorological disturbances that induce a weak ICU (thermal differences less than 2 °C).

Although the mountainous site, Emiliano Zapata, has an area and population 1:10 relative to the coastal site, it does have an ICU, with a higher temperature in the central urban area, compared to its surroundings where vegetated areas predominate. The average ICU intensity is weak, 1.5 ºC.

It is worth mentioning that the analysis of atmospheric temperature alone is limited because multiple additional factors, such as wind, atmospheric humidity, and anthropogenic heat emissions, influence the ICU genesis and evolution.

Based on the results and experience gathered in this study, we recommend continuing data recording efforts to extend the ICU study period and include other seasons of the year to have a more detailed characterization. While driving tours have proven to be a suitable method for ICU recording in urban areas, setting a relatively dense network of fixed rooftop stations may improve the analysis and yield at least two ICU detection levels (within the urban canopy through drive tours and above it by fixed stations). Infrared satellite images could supplement the analysis to represent the phenomenon at three levels: ground, canopy, and above-canopy.

Palavras-chave : urban heat island; mobile transects; coastal site; mountainous site; urban canopy.

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