Potential influence of deforestation on rainfall stretches well beyond climatic regions

Abstract. Human-induced changes in land cover, especially deforestation, impact the regional and global water cycle. However, the effects of actual deforestation on the change in downwind precipitation have not been fully quantified on a global scale. Here, we present a newly developed measure called 'precipitation potentially impacted by deforestation', or in short, deforestation impact (ID). We combined datasets of moisture source-sink relations and recent actual deforestation (2001–2019) to calculate how much of the moisture flow is disrupted by deforestation. The deforestation impact in the Amazon and La Plata basins are most affected, with some cells potentially having lost over 16 % of their usual moisture flows due to recent deforestation. Other notable areas are high-latitude boreal regions in North America and Eurasia, as well as the tropical regions of South-East Asia and West and Central Africa. When calculating the deforestation impact as percentage of the continentally recycled precipitation, the South-East Asia region finds itself potentially losing over 50 % of their usual land-based moisture flows to recent deforestation. Regions in the northern half of South America, as well as the South-East US and South-West Canada show notable impacts on the continentally recycled precipitation. Most regions (28 out of 43) are primarily impacted by deforestation outside the region itself, with almost half (21 out of 43) showing even over 70 % of deforestation impact originating from deforestation outside of the region. Most tropical regions have higher than average ID as well as high internal ID, suggesting that moisture recycling is stronger on this scale for tropical regions compared to nontropical regions. We overlaid deforestation impact with actual precipitation trends, expressed by the normalized cumulative anomaly of 2001–2018 precipitation compared to the long-term (1980–2018) average. In contrast to some previous studies, we could not confirm a generic link between the calculated deforestation impact and precipitation trends. This, together with the large impact of deforestation from outside the region for most regions, suggests that moisture recycling is mostly relevant on scales larger than the current study regions, in line with earlier global studies, but contrasting with some regional studies. We postulate that water- and energy-limited areas have different sensitivities to deforestation-induced moisture loss. We acknowledge and stress that ID does not take into account the many other process changes and effects on the water cycle due to deforestation, which can be region specific. Further research is needed to separate direct and indirect feedback effects in deforestation impact and to understand better how we can protect our forests and water.