<p>The Amazon forest has recently experienced substantial human-induced loss of forest cover. However, the extent to which such historical deforestation has altered regional observed precipitation through inter-regional atmospheric moisture transport remains unclear. Here, we combine satellite observations and an atmospheric moisture tracking model to quantify these feedbacks over the past four decades (1980-2019). We identify a contrasting northern increase and southern decrease dipole trend in observed precipitation across the Amazon basin. The pronounced reduction in precipitation for the southern Amazon basin reaches up to 3.9-5.4 mm yr^-1 per year, resulting in an 8-11% decline in annual precipitation across the observation period. We discover that this reduction in precipitation is primarily (52-72%) related to widespread deforestation in the southern basin and upwind regions over South America. Deforestation substantially suppresses forest-sourced moisture, increases atmospheric stability and moisture outflow, leading to precipitation reduction. We also find that climate models substantially underestimate the sensitivity of precipitation to deforestation, implying that the Amazon forest is at risk of major loss much sooner than previously projected.</p>