Areas susceptible to desertification in Brazil: An approach based on the frequency of annual aridity classes

The expansion of arid lands is one of the most critical environmental threats of the century, driven by climate change and unsustainable human activities. In Brazil, recent climatic shifts suggest an expansion of arid and semi-arid zones beyond the traditionally vulnerable Northeast region. While prior research has emphasized long-term climatological trends focused in that region, this study adopts non-stationary approaches to examine year-by-year aridity class frequencies from 1961 to 2020 across the entirety of Brazil. It also distinguishes the relative influence of precipitation (P) and potential evapotranspiration (PET) on observed aridity index (AI) changes. Our results reveal an expansion of roughly 30 % of dryland conditions across Brazil over the past 30 years, extending beyond the traditionally semi-arid Northeast into the Southeast, and an emerging hotspot in the Pantanal, potentially linked with larger scale South American aridization trends. The increasing annual frequency of arid and semi-arid classifications, particularly in emerging zones, suggests a persistent shift towards drier climates. This pattern seems to be driven primarily by declining P and secondarily by rising PET (temperature). By analyzing annual frequencies, we uncover a creeping aridity process, which directly converses with updated desertification risk assessments and climate adaptation strategies in Brazil, such as the ‘Brazilian Action Plan to Combat Desertification and Mitigate the Effects of Drought’.