Estimation of anthropogenic heat flux in a city in the Central Amazon

The climate in the city of Manaus (AM) already suffers from the effects of anthropogenic activities, which has modified the surface energy balance leading to warming. Therefore, the main objective of this research was to determine the magnitude, daily variation, and spatial distribution of anthropogenic heat flux ( Q AH ) in the urban area of Manaus. This city is the capital of the state of Amazonas, located in the northern region of Brazil, and stands out for its unique location, surrounded by the Amazon Rainforest along the banks of the Negro river. This distinctive setting becomes the focus of the research, providing a unique opportunity to thoroughly examine the interaction and influence of urbanization. For this, the top-down inventory-based method was used to estimate the Q AH , using information from the population's fuel and electrical consumption and metabolic heat production. In the urban area of Manaus, the vehicular, stationary, and metabolic sources were responsible for 57.59%, 30.06%, and 12.35% of the total anthropogenic heat flux, referring to the diurnal cycle. Those distributed during a day reached an average of 13.04 W/m 2 , with maximum values of 17.37 W/m 2 between 18:00 and 19:00 LT and a minimum of 7.27 W/m 2 between 23:00 and 00:00 LT. In addition, the city exhibits daily behavior with three Q AH maximums. These results indicate that the Q AH is directly influenced by the hourly population dynamics with higher traffic at three times: 07:00 and 08:00 LT, 14:00 and 15:00 LT, and 18:00 and 19:00 LT. For the spatial distribution of anthropogenic heat in Manaus, the annual average for the entire urban area was 12.91 W/m 2 in 2013 and 13.16 W/m 2 in 2014, resulting in an average of 13.04 W/m 2 for the two-year database presented in this study, with variations among neighborhoods. Those differences were observed in areas of high and low residential density, with average fluxes ranging between 20.36 W/m 2 and 6.38 W/m 2 , respectively. Spatial heterogeneity was evident, with higher magnitudes correlated to densely populated neighborhoods, such as Santa Luzia and Betânia, reaching values above 30 W/m 2 . These results underscore the critical influence of population density on the spatial distribution of anthropogenic heat in the city. The results found could assist planning and management of cities, especially in areas with intense urbanization, which produce greater Q AH . In addition, it increases knowledge by providing more realistic information about Manaus to improve future studies on local climate, such as urban heat island behavior, energy balance closure, and numerical simulations.