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• Deforestation-induced rainfall changes negatively impact soybean and maize yields in Brazil. • Soybean and maize yields could have been 6.6 % and 9.9 % higher per year if rainfall patterns hadn't been altered by deforestation. • Agricultural efficiency improvements insufficient to counteract rainfall-changes effects on yields. • Study underscores the vital role of forest preservation for agricultural resilience and food security. • Forests' critical role in regulating the water cycle highlighted in the face of climate change. Whereas the global demand for food, fiber and energy is increasing, the capacity of ecosystems services to sustain agricultural production is being compromised worldwide. Brazil is a global food supplier that has benefitted from agricultural intensification in the past decades. At the same time, expansion of cropland has led to deforestation that, in turn, is increasingly affecting rainfall patterns thereby influencing crop yields. This study examines how loss in forest cover has impacted agricultural yields through change in rainfall. To do so, we use modelled data on changes in rainfall patterns due to deforestation as input to a crop model. We assess yield changes within the soybean-maize double cropping system, the country's most relevant agricultural system, in five states within the Amazon and Cerrado biomes. Findings revealed that soybean and maize yields would have been respectively 6.6 % and 9.9 % higher per year in the last decade if rainfall patterns hadn't been altered by deforestation from 1982 onwards. Although agricultural efficiency improved between 2011 and 2020, it was insufficient to offset the negative effect of altered rainfall on yields. Our paper reveals the link between deforestation and crop yields, emphasizing the need to preserve forest cover for agricultural resilience and food security. It reinforces the critical role of forests in regulating the water cycle, particularly in the face of climate change-induced warmer and drier conditions that can impact agricultural production and other human activities. [ABSTRACT FROM AUTHOR]

Despite recent advances in modeling forest-rainfall relationships, the current understanding of changes in observed rainfall patterns resulting from historical deforestation remains limited. To address this knowledge gap, we analyzed how 40 years of deforestation has altered rainfall patterns in South America as well as how current Amazonian forest cover sustains rainfall. First, we develop a spatiotemporal neural network model to simulate rainfall as a function of vegetation and climate inputs in South America; second, we assess the rainfall effects of observed deforestation in South America during the periods 1982-2020 and 2000-2020; third, we assess the potential rainfall changes in the Amazon biome under two deforestation scenarios. We find that, on average, cumulative deforestation in South America from 1982 to 2020 has reduced rainfall over the period 2016-2020 by 18% over deforested areas, and by 9% over non-deforested areas across South America. We also find that more recent deforestation, that is, from 2000 to 2020, has reduced rainfall over the period 2016-2020 by 10% over deforested areas and by 5% over non-deforested areas. Deforestation between 1982 and 2020 has led to a doubling in the area experiencing a minimum dry season of 4 months in the Amazon biome. Similarly, in the Cerrado region, there has been a corresponding doubling in the area with a minimum dry season of 7 months. These changes are compared to a hypothetical scenario where no deforestation occurred. Complete conversion of all Amazon forest land outside protected areas would reduce average annual rainfall in the Amazon by 36% and complete deforestation of all forest cover including protected areas would reduce average annual rainfall in the Amazon by 68%. Our findings emphasize the urgent need for effective conservation measures to safeguard both forest ecosystems and sustainable agricultural practices., (© 2023 The Authors. Global Change Biology published by John Wiley & Sons Ltd.)