Current deforestation in the Amazon is already depleting rainfall over the region, and climate change is worsening this trend of drying, say researchers in a new study, which may ultimately bring the world's biggest tropical rainforest closer to a critical threshold. These findings are published recently in Geophysical Research Letters, and do not only reveal interactions between land-use change and warming regional climate, but also provide effective suggestions for improving the understanding of climate change in regions where natural climate variability is still insufficiently recognised.  

The role of trees in the recycling of moisture in the Amazon has long been known and understood. Trees take up water from the soil and give it off to the air via transpiration, which is the key factor in contributing to the rain that falls on the forest. But extensive agricultural development, fallow land and development for infrastructure limit this moisture recycling, which leads to decreased rainfall and an increased risk of drought. These new findings estimate the effects deforestation already has on regional precipitation. 

With models that determined how climate change would impact water production without the influences of deforestation, figures from different areas of the basin were suggested to indicate that rainfall has already declined by several percentage points because of deforestation. The decrease is substantial when the reduction is added to the warming effects of increasing levels of greenhouse gases, particularly in the dry season when the forest is most at risk. These factors may take the Amazon to a drier state, similar to a savanna, with far-reaching implications for the entire river basin, the scientists warn. This change would result in a reduction of biodiversity and carbon storage, and also cause changes in rainfall outside of South America that may impact agriculture and water supply.  

Lead authors highlight the necessity of safeguarding and revitalising the forests as an integral approach to climate strategy. Halting deforestation now may help mitigate feedback between the decline in rainfall and the decrease in forest cover, while reducing GHG emissions is important. If the Amazon is not stopped from continuing to decline, its ability to sustain itself and regulate the climate may be at risk, making sections of the world's largest rainforest vulnerable to exceeding critical ecological tipping points.