Increased dry-season length over southern Amazonia in recent decades and its implication for future climate projection

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 110; no. 45; pp. 18110 - 18115
• Main Authors: Fu, Rong, Yin, Lei, Li, Wenhong, Arias, Paola A., Dickinson, Robert E., Huang, Lei, Chakraborty, Sudip, Fernandes, Katia, Liebmann, Brant, Fisher, Rosie, Myneni, Ranga B.
• Format: Journal Article
• Language: English
• Published: Washington, DC NATIONAL ACADEMY OF SCIENCES 05-11-2013; National Acad Sciences; National Academy of Sciences
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Atmospherics; Biological and medical sciences; Brazil; Climate change; Climate Change - history; Climate models; Climatology; Climatology. Bioclimatology. Climate change; Datasets; Drought; Earth, ocean, space; Exact sciences and technology; External geophysics; Fundamental and applied biological sciences. Psychology; Global climate models; History, 20th Century; History, 21st Century; Meteorology; Models, Theoretical; Oceans; Physical Sciences; Rain; Seasons; Simulation; Simulations; Synecology; Terrestrial ecosystems; Trees; Tropical rain forests; South America; Amazonia; Amazon Basin; Brazil; South America, Amazonia; IS, Tropical Pacific; Terrestrial environment; climate model projection; atmospheric precipitation; climate warming; Tropical rain forest; climate variability; Forest decline; Climate prediction; duration; Bioclimatology; Dry season; Timing; rainforests; climate change
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1302584110

We have observed that the dry-season length (DSL) has increased over southern Amazonia since 1979, primarily owing to a delay of its ending dates (dry-season end, DSE), and is accompanied by a prolonged fire season. A poleward shift of the subtropical jet over South America and an increase of local convective inhibition energy in austral winter (June–August) seem to cause the delay of the DSE in austral spring (September–November). These changes cannot be simply linked to the variability of the tropical Pacific and Atlantic Oceans. Although they show some resemblance to the effects of anthropogenic forcings reported in the literature, we cannot attribute them to this cause because of inadequate representation of these processes in the global climate models that were presented in the Intergovernmental Panel on Climate Change's Fifth Assessment Report. These models significantly underestimate the variability of the DSE and DSL and their controlling processes. Such biases imply that the future change of the DSE and DSL may be underestimated by the climate projections provided by the Intergovernmental Panel on Climate Change's Fifth Assessment Report models. Although it is not clear whether the observed increase of the DSL will continue in the future, were it to continue at half the rate of that observed, the long DSL and fire season that contributed to the 2005 drought would become the new norm by the late 21st century. The large uncertainty shown in this study highlights the need for a focused effort to better understand and simulate these changes over southern Amazonia.