Cross-Border Contrast in Roof Albedos: Cd. Juárez, Chihuahua vs. El Paso, Texas

Abstract:

The El Paso-Juárez metroplex is a binational community along the US-Mexico border across the Río Grande. The twin cities lie within the Chihuahuan desert climate zone, where the intense summer heat is a significant health hazard for the 2.7 million residents in all. The National Weather Service predicts increasing surface temperatures in the region due to global warming. Climate data also show Juárez tends to be cooler than El Paso by a few degrees Celsius. Satellite imagery indicates a distinct albedo contrast between the neighboring cities. A point-counting technique confirmed that white residential roofs predominate in Juárez with 27%, whereas only 7% of El Paso residences have white roofs. Furthermore, Juárez has 16% fewer dark residential roofs than El Paso. The ratio of light to dark roofs in El Paso may contribute to the heat load in the city. A total of 2,116 residences were counted for El Paso and 2,534 for Juárez. Residential roofs comprised of 22% and 26% of all point counts for each city, respectively; other point types included roads, parking lots, walkways, vehicles, vegetation, soil, rocks, and water sources. El Paso ranks among the top 10 US cities with a large Hispanic population and shares cultural roots with Juárez. However, the surface and roofing materials typically found in Juárez tend to be lighter, resulting in a reduced heat burden; higher poverty in Mexico may call for cheaper material choices. Likewise, the higher population density in Juárez yields a higher roof density, increasing the proportion of reflective surface area of roofs. Dirt roads and gravel paths prevalent in Juárez, which also act as reflective surfaces, accounted for 16% of counts. Interestingly, houses in affluent neighborhoods in both cities have white or lighter roof shades. The median income for El Paso and Juárez is less than $45,000; many residents can only afford evaporative coolers or fans, leading to excessive heat exposure. Educating the public, industry, and policymakers to implement white roofs in new or existing homes can moderate the summer heat and mitigate the effects of urban heat islands in El Paso; the likelihood of heat-related symptoms may decrease by improving residential resilience to extreme heat. Future work will quantify roof albedos and examine city demographics, roofing materials, roofing industry, and policy.