Chandrakant Singh , Ruud van der Ent, Ingo Fetzer, Lan Wang-Erlandsson

Tropical rainforests invest in their root systems to store soil moisture from water-rich periods for use in water-scarce periods. An inadequate root-zone soil moisture storage predisposes or forces these forest ecosystems to transition to a savanna-like state, devoid of their native structure and functions. Yet changes in soil moisture storage and its influence on the rainforest ecosystems under future climate change remain uncertain. Using the empirical understanding of root zone storage capacity, we assess the future state of the rainforests and the forest-savanna transition risk in South America and Africa under four different shared socioeconomic pathway scenarios. We find that by the end of the 21st century, nearly one-third of the total forest area will be influenced by climate change. Furthermore, beyond 1.5-2⁰C warming, ecosystem recovery reduces gradually, whereas the forest-savanna transition risk increases several folds. For Amazon, this risk can grow by about 1.5-6 times compared to its immediate lower warming scenario, whereas for Congo, this risk growth is not substantial (0.7-1.65 times). The insight from this study underscores the urgent need to limit global surface temperatures below the Paris agreement.