Brazilian heatwaves are shifting towards dry-hot thermodynamic regimes in transformed landscapes

Abstract

Heatwaves are intensifying globally, but their impacts depend strongly on the atmospheric moisture conditions under which extreme heat occurs. We show that Brazilian heatwaves underwent preferential dry-hot amplification during 1990–2024. Hourly ERA5 reanalysis was converted into daily thermodynamic diagnostics to classify general, humid, dry-hot, and compound dry-hot/stagnant heatwaves. General heatwaves showed widespread increases in frequency, cumulative duration, and intensity, whereas humid-heatwave trends were weak and spatially fragmented. Dry-hot heatwaves intensified coherently across central and southeastern Brazil, including the Cerrado, MATOPIBA, the southern Amazon–Cerrado transition, Pantanal, and parts of the Caatinga/Semi-arid region. Using a common Tmax-only severity metric, dry-hot amplification exceeded humid amplification across much of Brazil, with a positive DHW − HHW contrast over 73.6% of the country. This pattern was spatially associated with increasing vapour-pressure deficit and declining relative humidity. Cumulative landscape state was more consistently associated with the DHW − HHW contrast than recent land-cover change, although landscape–atmosphere relationships were regionally heterogeneous. VPD decomposition showed that atmospheric drying reflected both warming-driven increases in saturation demand and regional changes in actual vapour pressure, rather than a uniform decline in atmospheric moisture. Spatially robust controlled models supported positive associations among transformed land, evaporative demand, and dry-hot amplification, while accounting for spatial dependence and without implying causality or mediation. The DHW − HHW contrast remained positive under alternative VPD and wet-bulb thresholds, although its magnitude was sensitive to minimum event duration. Temporal tests showed that recent extremes strengthened, but did not generate, the multi-decadal dry-hot signal. Brazilian heatwave trends therefore show preferential amplification under dry-hot conditions, with implications for vegetation water stress, agriculture, ecosystem vulnerability, and fire-conducive weather.