NEIGHBORHOOD EXPOSURE TO NIGHTTIME HEAT IN A DESERT CITY ― EL PASO, TEXAS

Rapid urbanization and population growth transform the natural landscape into anthropogenic urban land, and alter such surface physical properties as albedo, energy balance, and surface roughness. Cities are warmer than the surrounding rural lands, even deserts, a phenomenon called Urban Heat Island.

Although there are many studies of variation of land surface temperature during daytime, less is known about such variation during nighttime. We determined the spatial variation of summer nighttime land surface temperatures at the neighborhood level in El Paso, Texas, using infrared satellite imagery. Our long-term goal is to determine whether residents in specific neighborhoods are at excess risk of morbidity due to heat stress and other factors associated with high temperatures, e.g., sleep deprivation, irritability, etc. We consider nighttime temperature to be of significant importance because it is spent in the home and most El Paso residents do not have “refrigerated” air conditioning, but instead rely on less expensive and less effective evaporative cooling. We also examined the correlation of total population, income, poverty, and age over 65 with surface temperature during the summer months between 1990 and 2010.

The results showed a strong association between land surface temperature and the normalized difference vegetation index, population density, and albedo, especially during daytime. Population density showed a higher correlation with temperature during the night, which further indicated the urban heat island effect. In the geographically weighted regression model four variables collectively explained between 71% and 82% of the variance of land surface temperature during daytime and from 46% to 69% during nighttime. Vegetation was a cooling factor in the daytime and to a lesser degree at night. Population density acted as a warming factor during both day and nighttime. Albedo and elevation were weaker explanatory variables during both day and nighttime.

Day and nighttime temperature increased over the urban area through the last 20 years. This suggests that El Paso residents will be subjected to increased heat vulnerability in the future due to the combined effects of anticipated urban growth and global warming. Similar vulnerability can be expected in other cities in the US desert Southwest.