Rising Thermal Extremes and Seasonal Particulate Exposure in Western Mato Grosso, Brazil (2000-2025): An Environmental Exposure Profile and the Case for Health Surveillance

Vollständiger Abstract

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The western margin of the Pantanal meets the southern edge of the Amazonian deforestation arc, and each dry season its population breathes what the fires leave behind. Yet the small municipalities along this margin are among the least monitored in Brazil, and the exposure their residents carry has never been quantified. We characterised thermal and particulate exposure across 21 municipalities of western Mato Grosso between 2000 and 2025, counting days rather than months above health-relevant thresholds. Daily air temperature, dew point and precipitation came from ERA5-Land; the heat index was computed daily from maximum temperature and the relative humidity concurrent with it, derived from dew point. Fine particulate matter was characterised independently from two validated products, the ACAG satellite-derived estimate (2000-2022) and the NASA GEOS-CF composition reanalysis (2018-2025), and burned area from MODIS MCD64A1. Trends were tested with a Mann-Kendall test modified for serial correlation and the Theil-Sen estimator, with false discovery rate correction across municipalities. Days with a heat index above 39 °C, the NOAA danger level, rose from 8.4 per year in 2000-2009 to 21.4 in 2016-2025; days with maximum temperature above 36 °C rose from 6.5 to 23.1; days with afternoon relative humidity below 30 per cent, the Brazilian meteorological service attention level, rose from 14.1 to 28.7. Maximum temperature rose by 0.394 °C per decade and was significant in all 21 municipalities after correction. Particulate matter showed no trend in either product, but a pronounced seasonal cycle peaking in September at 47.7 and 47.1 µg m⁻³ respectively, closely tracking burned area. Thermal danger and particulate load therefore diverge in direction and are offset in timing, the smoke maximum falling in September and the thermal maximum in October. This is an exposure profile rather than evidence of harm. Even so, a population whose days of thermal danger have more than doubled in a quarter century, and whose dry-season air remains heavily loaded, warrants systematic surveillance of respiratory and cardiovascular outcomes.