Analysis of patterns, drivers, and trends of Surface Urban Heat Islands (SUHIS) in Brazil

Abstract

The expansion of urban areas occurs by changing natural surfaces, bringing environmental effects like modifications in the surface energy balance and the formation of surface urban heat islands (SUHIs). The spatial-temporal variation of SUHIs intensities (SUHIIs) and their relationship with surface biophysical parameters in Brazilian metropolitan regions (MRs) need to be better explored, especially taking into consideration the continuous monthly and annual evolution of urbanisation. This study aims then to provide baseline information on the influence of urbanisation in the expansion of SUHIs and the variability of biophysical parameters in twenty-one major Brazilian MRs from 2003 to 2022. We used land surface temperature (LST) data from MODIS (MOD11A2 and MYD11A2) sensors to continuously quantify the daytime and nighttime SUHIIs. Spectral reflectance from MODIS (MOD09Q1, MYD09Q1, MOD09A1, and MYD09A1) and reanalysis data (GLDAS 2.1 and ERA5-Land) were used to access the variability of Enhanced Vegetation Index-2 (EVI2), surface albedo (α), urban areas (UAs) growth, surface net radiation (Rn), and actual evapotranspiration (ET) at 250-m spatial resolution. The Mann-Kendall trend test was applied for all variables, and their relationships with LST were investigated through Pearson correlation (r), determination coefficient (R2) and Kling-Gupta Efficiency (KGE). The results show that the SUHIs were 60% (1.64 ºC) higher during the daytime, with significant growth trends along the studied period and more pronounced monthly seasonal variations in higher latitudes MRs holding subtropical climate zones. The UAs showed to be more influential on LST during daytime, with the association of LST with EVI2 and α playing a fundamental role in regulating the urban climate. The results also demonstrated that increasing ET potentially mitigates LST, especially during the daytime. Rn highest influenced the nighttime LST, leading to a higher availability of sensible heat during this period. The results found from this study provide a nuanced understanding of the factors influencing the spatiotemporal dynamics of SUHIIs in the largest MRs of Brazil, contributing valuable insights for urban planning and climate mitigation strategies.