Increasing and widespread vulnerability of intact tropical rainforests to repeated droughts

Shengli Tao (1, 2) , Jérôme Chave (1) , Pierre-Louis Frison (3) , Thuy Le Toan (4) , Philippe Ciais (5) , Jingyun Fang (2) , Wigneron J.-P. (6) , Maurizio Santoro (7) , Hui Yang (5) , Xiaojun Li (6) , Nicolas Labrière (1) , Sassan Saatchi (8)

1 EDB - Evolution et Diversité Biologique
2 Peking University [Beijing]
3 LaSTIG - Laboratoire sciences et technologies de l'information géographique
4 CESBIO - Centre d'études spatiales de la biosphère
5 LSCE - Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette]
6 UMR ISPA - Interactions Sol Plante Atmosphère
7 Gamma Remote Sensing Research and Consulting AG
8 JPL - Jet Propulsion Laboratory

Intact tropical rainforests have been exposed to severe droughts in recent decades, which may threaten their integrity, their ability to sequester carbon, and their capacity to provide shelter for biodiversity. However, their response to droughts remains uncertain due to limited high-quality, long-term observations covering extensive areas. Here, we examined how the upper canopy of intact tropical rainforests has responded to drought events globally and during the past 3 decades. By developing a long pantropical time series (1992 to 2018) of monthly radar satellite observations, we show that repeated droughts caused a sustained decline in radar signal in 93%, 84%, and 88% of intact tropical rainforests in the Americas, Africa, and Asia, respectively. Sudden decreases in radar signal were detected around the 1997–1998, 2005, 2010, and 2015 droughts in tropical Americas; 1999–2000, 2004–2005, 2010–2011, and 2015 droughts in tropical Africa; and 1997–1998, 2006, and 2015 droughts in tropical Asia. Rainforests showed similar low resistance (the ability to maintain predrought condition when drought occurs) to severe droughts across continents, but American rainforests consistently showed the lowest resilience (the ability to return to predrought condition after the drought event). Moreover, while the resistance of intact tropical rainforests to drought is decreasing, albeit weakly in tropical Africa and Asia, forest resilience has not increased significantly. Our results therefore suggest the capacity of intact rainforests to withstand future droughts is limited. This has negative implications for climate change mitigation through forest-based climate solutions and the associated pledges made by countries under the Paris Agreement.

Mots clés: rainforests; drought; remote sensing; radar

Domaines: Bioclimatologie; Biodiversité et Ecologie; Sylviculture, foresterie

Shengli Tao, Jérôme Chave, Pierre-Louis Frison, Thuy Le Toan, Philippe Ciais, et al.. Increasing and widespread vulnerability of intact tropical rainforests to repeated droughts. Proceedings of the National Academy of Sciences of the United States of America, 2022, 119 (37), pp.2116626119. ⟨10.1073/pnas.2116626119⟩. ⟨hal-03787959⟩