Via Eurekalert – New study debunks myths about Amazon rain forests – They may be more tolerant of droughts than previously thought

(Boston) — A new NASA-funded study has concluded that Amazon rain forests were remarkably unaffected in the face of once-in-a-century drought in 2005, neither dying nor thriving, contrary to a previously published report and claims by the Intergovernmental Panel on Climate Change.

“We found no big differences in the greenness level of these forests between drought and non-drought years, which suggests that these forests may be more tolerant of droughts than we previously thought,” said Arindam Samanta, the study’s lead author from Boston University.

The comprehensive study published in the current issue of the scientific journal Geophysical Research Letters used the latest version of the NASA MODIS satellite data to measure the greenness of these vast pristine forests over the past decade.

A study published in the journal Science in 2007 claimed that these forests actually thrive from drought because of more sunshine under cloud-less skies typical of drought conditions. The new study found that those results were flawed and not reproducible.

“This new study brings some clarity to our muddled understanding of how these forests, with their rich source of biodiversity, would fare in the future in the face of twin pressures from logging and changing climate,” said Boston University Prof. Ranga Myneni, senior author of the new study.

The IPCC is under scrutiny for various data inaccuracies, including its claim – based on a flawed World Wildlife Fund study — that up to 40% of the Amazonian forests could react drastically and be replaced by savannas from even a slight reduction in rainfall.

“Our results certainly do not indicate such extreme sensitivity to reductions in rainfall,” said Sangram Ganguly, an author on the new study, from the Bay Area Environmental Research Institute affiliated with NASA Ames Research Center in California.

“The way that the WWF report calculated this 40% was totally wrong, while [the new] calculations are by far more reliable and correct,” said Dr. Jose Marengo, a Brazilian National Institute for Space Research climate scientist and member of the IPCC.

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Geophysical Research Letters article citation: Samanta, A., S. Ganguly, H. Hashimoto, S. Devadiga, E. Vermote, Y. Knyazikhin, R. R. Nemani, and R. B. Myneni (2010), Amazon forests did not green‐up during the 2005 drought, Geophys. Res. Lett., 37, L05401, doi:10.1029/2009GL042154.

ABSTRACT: Amazon forests did not green-up during the 2005 drought

Paper available here (PDF)

The sensitivity of Amazon rainforests to dry-season droughts is still poorly understood, with reports of enhanced tree mortality and forest fires on one hand, and excessive forest greening on the other. Here, we report that the previous results of large-scale greening of the Amazon, obtained from an earlier version of satellite-derived vegetation greenness data – Collection 4 (C4) Enhanced Vegetation Index (EVI), are irreproducible, with both this earlier version as well as the improved, current version (C5), owing to inclusion of atmosphere-corrupted data in those results. We find no evidence of large-scale greening of intact Amazon forests during the 2005 drought – approximately 11%–12% of these drought-stricken forests display greening, while, 28%–29% show browning or no-change, and for the rest, the data are not of sufficient quality to characterize any changes. These changes are also not unique – approximately similar changes are observed in non-drought years as well. Changes in surface solar irradiance are contrary to the speculation in the previously published report of enhanced sunlight availability during the 2005 drought. There was no co-relation between drought severity and greenness changes, which is contrary to the idea of drought-induced greening. Thus, we conclude that Amazon forests did not green-up during the 2005 drought. h/t to Dr. Leif Svalgaard

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