The impact of urbanization on heat stress in Brazil: A multi-city study

Abstract

This study focuses on local climate modifications as observed in historical records of climate normals and in reanalysis-derived thermal stress data for two years unaffected by El Niño (1985 and 2020) across an approximately southeast-northwest transect over the Brazilian territory. Six major cities were analyzed, namely Porto Alegre, Curitiba, Brasília, Cuiabá, Porto Velho, and Manaus, each characterized by distinct climatic conditions. Climate normals were obtained from the network of the Brazilian Institute of Meteorology (INMET) whereas heat stress data represented by the Universal Thermal Climate Index (UTCI) were retrieved from the ERA5-HEAT reanalysis dataset. Urbanization was interpreted as changes in impervious surfaces observed from satellite imagery, which allowed us to identify the growth and spread of the impervious area in the cities. A consistent but not uniform rise in temperature and heat stress was found in the evaluated locations, with a more pronounced rise in heat stress in low-latitude locations. Among temperature- and thermal stress-related variables, the increase in impervious surfaces appears to correlate more strongly to a rise in maximum temperatures and in the average UTCI, with statistically significant impact on changes in the ‘moderate heat stress’ class of the UTCI. The consideration of the breakdown of degrees of imperviousness over urban areas has been found to be more defining of changes in local climate conditions than the bulk change in impervious surfaces over time.