Atmospheric brown clouds (ABCs), composed of black carbon, organic carbon, and dust, significantly impact South Asian climate and hydrological cycles. Since the 1930s, increased emissions of SO₂ and black carbon have led to higher atmospheric concentrations of aerosols, resulting in reduced solar radiation, decreased evaporation, and reduced monsoon rainfall. These changes are linked to atmospheric stability and reduced sea surface temperature gradients in the Northern Indian Ocean. Simulations using a coupled ocean-atmosphere model show that ABCs contribute to surface cooling, reduced evaporation, and weakened monsoon rainfall, masking up to 50% of the warming from greenhouse gases. ABCs also alter atmospheric heating patterns, affecting monsoon rainfall distribution and increasing drought frequency. The study highlights the role of ABCs in regional climate changes and suggests that current emission trends could lead to a doubling of drought frequency in the coming decades. The findings emphasize the importance of addressing air pollution to mitigate its impacts on climate and water resources in South Asia.Atmospheric brown clouds (ABCs), composed of black carbon, organic carbon, and dust, significantly impact South Asian climate and hydrological cycles. Since the 1930s, increased emissions of SO₂ and black carbon have led to higher atmospheric concentrations of aerosols, resulting in reduced solar radiation, decreased evaporation, and reduced monsoon rainfall. These changes are linked to atmospheric stability and reduced sea surface temperature gradients in the Northern Indian Ocean. Simulations using a coupled ocean-atmosphere model show that ABCs contribute to surface cooling, reduced evaporation, and weakened monsoon rainfall, masking up to 50% of the warming from greenhouse gases. ABCs also alter atmospheric heating patterns, affecting monsoon rainfall distribution and increasing drought frequency. The study highlights the role of ABCs in regional climate changes and suggests that current emission trends could lead to a doubling of drought frequency in the coming decades. The findings emphasize the importance of addressing air pollution to mitigate its impacts on climate and water resources in South Asia.