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Risk of drying in the Amazon Basin: NASA Satellites Detect Extensive Drought Impact on Amazon Forests
El verano pasado hubo una sequía sin precedentes en el Amazonas y dos equipos espaciales de la NASA observaron sus efectos. La selva no recuperó su estado normal hasta bastante después de terminar el período seco, a finales de octubre de 2010. "El verdor de la vegetación, que es una medida de su salud, disminuyó en un área superior a tres veces y media el Estado de Texas", explica Liang Xu (Universidad de Boston), que lidera la investigación.
La sensibilidad a la sequía de la selva amazónica se está estudiando intensamente. Los modelos de proyección climática indican que en el futuro el aumento de las temperaturas y la alteración de los patrones de precipitaciones pueden disminuir la humedad en la región, provocando una sustitución de la selva húmeda por vegetación tipo sabana leñosa o praderas, explican los expertos de la NASA. Esto supondría la emisión a la atmósfera del carbono almacenado en la madera putrefacta, lo que aceleraría el calentamiento global. El Panel Intergubernamental sobre Cambio Climático (IPCC), de Naciones Unidas, ya alertó acerca del riesgo de que la Amazonía sufra en el futuro fuertes sequías más frecuentemente que ahora.
El equipo científico ha analizados los datos correspondientes a más de una década tomados por los instrumentos de la NASA MODIS (un espectroradiómetro) y TRMM (en colaboración con la agencia japonesa Jaxa) obteniendo así mapas detallados del verdor decreciente de la vegetación desde la sequía de 2010 en la Amazonía. Los resultados de la investigación se publicarán en la revista Geophysical Research Letters.
En los mapas se observa la reducción del verdor en un área de unos dos millones y medio de kilómetros cuadrados, lo que significa más de cuatro veces el área afectada en la región por la sequía de 2005. "Los datos de vegetación del Modis sugieren un impacto mayor, más extenso y más prolongado en la vegetación amazónica de lo que se puede inferir sólo a partir de los datos de precipitaciones", apunta Aridam Samanta (Atmospheric and Environmental Research Inc.).
Pero la gravedad de la sequía de 2010 se apreció también en los registros de los niveles del agua de los ríos de la cuenca del Amazonas, incluyendo el rio Negro. Esos niveles empezaron a descender en agosto del año pasado, alcanzaron un récord a finales de octubre y sólo empezaron a recuperarse con la llegada de las lluvias. "El año pasado fue el más seco en la región desde que se tienen registros del nivel de agua del Río Negro, hace 109 años, en el puerto de Manao, afirma el científico brasileño Marco Costa (Universidad Federal de Viçosa).
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EVALUACIÓN DE NIVEL HÍDRICO DE LA AMAZONÍA PRESENTA PROBLEMAS METODOLÓGICOS
El calentamiento climático debido a actividades humanas (calentamiento climático ANTROPOGÉNICO) se acompaña de cambios del ciclo hidrológico. Las economías, las sociedades y los ecosistemas en América del Sur son vulnerables a tales variaciones de los recursos hídricos. Por lo tanto, las evaluaciones del recurso agua y su impacto en las sociedades, así como de la adaptación correspondiente y las políticas de mitigación del estrés hídrico, han atraído una mayor atención en América del Sur. Sin embargo, incertidumbres sustanciales permanecen en materia de evaluación del recurso agua que se basan en los modelos aceptados de Circulación Oceáno-Atmosféra. Esta incertidumbre en los modelos, varía desde humedad importante hasta sequía catastrófica. Mediante la aplicación de un método estadístico, se caracterizó la incertidumbre y se identificaron indicadores a escala mundial para medir la fiabilidad de las evaluaciones de los recursos hídricos en América del Sur. Se muestra que, aunque la evaluación de la media del conjunto sugiere bastante humedad en la mayor parte de América del Sur, las limitaciones de observación indican una mayor probabilidad de sequía en la cuenca del Amazonas. Por lo tanto, la excesiva dependencia en los modelos comunmente aceptados, pueden conducir a inadecuada toma de decisiones
Climate warming due to human activities will be accompanied by hydrological cycle changes. Economies, societies and ecosystems in South America are vulnerable to such water resource changes. Hence, water resource impact assessments for South America, and corresponding adaptation and mitigation policies, have attracted increased attention. However, substantial uncertainties remain in the current water resource assessments that are based on multiple coupled Atmosphere Ocean General Circulation models. This uncertainty varies from significant wetting to catastrophic drying. By applying a statistical method, we characterized the uncertainty and identified global-scale metrics for measuring the reliability of water resource assessments in South America. Here, we show that, although the ensemble mean assessment suggested wetting across most of South America, the observational constraints indicate a higher probability of drying in the Amazon basin. Thus, over-reliance on the consensus of models can lead to inappropriate decision making.
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(a) The first ΔR mode (mm per year per K). (b) The first ΔT mode (K/K). (c) The first ΔP mode (%/K). (d) The regression map between the expansion coefficient of the first ΔR mode and changes in vertical pressure velocity, averaged between 850 and 250…
(a) Regression maps between T0 (K) in the present climate and the expansion coefficient of the first ΔR mode. (b) Regression maps between P0 (mm per year) in the present climate and the first ΔR mode. (c) Regression maps between vertical pressure vel…
(a) Scatter plot of the expansion coefficient of the first ΔR mode (normalized by the inter-model standard deviation) and the T0 biases (K). (b) Scatter plot of the expansion coefficient of the first ΔR mode and the P0 biases (mm per day). (c) Scatte…
(a) Changes in runoff (mm per year per K) for the ensemble mean. (b) Changes in runoff (mm per year per K) for the observationally constrained best estimate.
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NASA satellite sensors, such as MODIS, showed an average pattern of greenness of vegetation on South America: Amazon forests which have very high leaf area are shown in red and purple
colors, the adjacent cerrado (savannas) which have lower leaf area are shown in shades of green, and the coastal deserts are shown in yellow colors.
Image Credit: Boston University/NASA
Red and orange identify areas where satellite measurements indicated reduced Normalized Difference Vegetation Index (first index of greenness) of the Amazon forest during the 2010
drought.
Image Credit: Boston University/NASA
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Red and orange identify areas where satellite measurements indicated reduced Enhanced Vegetation Index (second index of greenness) of the Amazon forest during the 2010 drought.
Image Credit: Boston University/NASA
A new NASA-funded study has revealed widespread reductions in the greenness of the forests in the vast Amazon basin in South America caused by the record-breaking drought of
2010.
"The greenness levels of Amazonian vegetation -- a measure of its health -- decreased dramatically over an area more than three and one-half times the size of
Texas and did not recover to normal levels, even after the drought ended in late October 2010," said Liang Xu, the study's lead author from Boston University.
The drought sensitivity of Amazon rainforests is a subject of intense study. Scientists are concerned because computer models predict that in a changing
climate with warmer temperatures and altered rainfall patterns the ensuing moisture stress could cause some of the rainforests to be replaced by grasslands or woody savannas. This would
cause the carbon stored in the rotting wood to be released into the atmosphere, which could accelerate global warming. The United Nations' Intergovernmental Panel on Climate Change (IPCC)
has warned that similar droughts could be more frequent in the Amazon region in the future.
The comprehensive study was prepared by an international team of scientists using more than a decade's worth of satellite data from NASA's Moderate Resolution
Imaging Spectroradiometer (MODIS) and Tropical Rainfall Measuring Mission (TRMM).
Analysis of these data produced detailed maps showing vegetation greenness declines from the 2010 drought. The study has been accepted for publication in
Geophysical Research Letters, a journal of the American Geophysical Union.
The authors first developed maps of drought-affected areas using thresholds of below-average rainfall as a guide. Next they identified affected vegetation
using two different greenness indices as surrogates for green leaf area and physiological functioning. The maps show the 2010 drought reduced the greenness of approximately 965,000 square
miles of vegetation in the Amazon -- more than four times the area affected by the last severe drought in 2005.
"The MODIS vegetation greenness data suggest a more widespread, severe and long-lasting impact to Amazonian vegetation than what can be inferred based solely
on rainfall data," said Arindam Samanta, a co-lead author from Atmospheric and Environmental Research Inc. in Lexington, Mass.
The severity of the 2010 drought was also seen in records of water levels in rivers across the Amazon basin. Water levels started to fall in August 2010,
reaching record low levels in late October. Water levels only began to rise with the arrival of rains later that winter.
"Last year was the driest year on record based on 109 years of Rio Negro water level data at the Manaus harbor. For comparison, the lowest level during the
so-called once-in-a-century drought in 2005, was only eighth lowest," said Marcos Costa, coauthor from the Federal University in Vicosa, Brazil.
As anecdotal reports of a severe drought began to appear in the news media during the summer of 2010, the authors started near real-time processing of massive
amounts of satellite data. They used a new capability, the NASA Earth Exchange (NEX), built for the NASA Advanced Supercomputer facility at the agency's Ames Research Center in Moffett
Field, Calif. NEX is a collaborative supercomputing environment that brings together data, models and computing resources.
With NEX, the study's authors quickly obtained a large-scale view of the impact of the drought on the Amazon forests and were able to complete the analysis by
January 2011. Similar reports about the impact of the 2005 drought were published about two years after the fact.
"Timely monitoring of our planet's vegetation with satellites is critical, and with NEX it can be done efficiently to deliver near-real time information, as
this study demonstrates," said study coauthor Ramakrishna Nemani, a research scientist at Ames. An article about the NEX project appears in this week's issue of Eos, the weekly newspaper of
the American Geophysical Union.
For more information about this study and the NEX project, visit:
For more information about the MODIS sensor and data products, visit:
For information about the Tropical Rainfall Measuring Mission, visit:
Ruth Dasso Marlaire
Ames Research Center, Moffett Field, Calif.
Find this article at:
http://www.nasa.gov/topics/earth/features/amazon_drought.html
Supplementary Figures S1-S12, Supplementary Table S1 and Supplementary References.
http://www.nature.com/ncomms/journal/v2/n3/extref/ncomms1252-s1.pdf
The authors declare no competing financial interests.
Observational constraints indicate risk of drying in
the Amazon ...15 Mar 2011 ... Observational constraints indicate risk of drying in the Amazon basin. Hideo Shiogama; Seita Emori; Naota Hanasaki; Manabu Abe ...
www.nature.com/uidfinder/10.1038/ncomms1252
Drought Threatens Amazon Basin17 Jul 2006
... But last year the worst drought in more than a century hit the Amazon basin, drying up tributaries more than a mile wide and prompting ...
www.commondreams.org/headlines06/0717-07.htm -
En caché -
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http://www1.nasa.gov/images/content/531001main_Amazon_LAI_full.jpg
En los mapas se observa la reducción del verdor en un área de unos dos millones y medio de kilómetros cuadrados, lo que significa más de cuatro veces el área afectada en la región por la sequía de 2005. "Los datos de vegetación del Modis sugieren un impacto mayor, más extenso y más prolongado en la vegetación amazónica de lo que se puede inferir sólo a partir de los datos de precipitaciones", apunta Aridam Samanta (Atmospheric and Environmental Research Inc.).
Pero la gravedad de la sequía de 2010 se apreció también en los registros de los niveles del agua de los ríos de la cuenca del Amazonas, incluyendo el rio Negro. Esos niveles empezaron a descender en agosto del año pasado, alcanzaron un récord a finales de octubre y sólo empezaron a recuperarse con la llegada de las lluvias. "El año pasado fue el más seco en la región desde que se tienen registros del nivel de agua del Río Negro, hace 109 años, en el puerto de Manao, afirma el científico brasileño Marco Costa (Universidad Federal de Viçosa).
Interpretation of Satellite-measured Greenness Variation of Amazon Forests
There is concern that in a warming climate the ensuing moisture stress could result in Amazonian rainforests being replaced by savannas, in which case the large reserves of carbon stored in these forests, about 100 billion tons, could be released to the atmosphere, which in turn would accelerate global warming significantly. Hence, the drought sensitivity of these forests is a subject of intense study – recent articles on the response and vulnerability of these forests to droughts illustrate the various complexities. Severe droughts such as those associated with the El Niño Southern Oscillation (ENSO), when the plant‐available soil moisture stays below a critical threshold level for a prolonged period, are known to result in higher rates of tree mortality and increased forest flammability.
During this decade, the Amazon region has suffered two severe droughts in the short span of five years – 2005 and 2010. Studies on the 2005 drought present a complex, and sometimes contradictory, picture of how these forests have responded to the drought. Now, on the heels of the 2005 drought, comes an even stronger drought in 2010, as indicated by record low river levels in the 109 years of bookkeeping. How has the vegetation in this region responded to this record-breaking drought? Here we report widespread, severe and persistent declines in vegetation greenness, a proxy for photosynthetic carbon fixation, in the Amazon region during the 2010 drought based on analysis of satellite measurements. The 2010 drought, as measured by rainfall deficit, affected an area 1.65 times larger than the 2005 drought – nearly 5 million km2 of vegetated area in Amazonia. The decline in greenness during the 2010 drought spanned an area that was four times greater (2.4 million km2 and more severe than in 2005. Notably, 51% of all drought-stricken forests showed greenness declines in 2010 (1.68 million km2 compared to only 14% in 2005 (0.32 million km2). These declines in 2010 persisted following the end of the dry season drought and return of rainfall to normal levels, unlike in 2005. Overall, the widespread loss of photosynthetic capacity of Amazonian vegetation due to the 2010 drought may represent a significant perturbation to the global carbon cycle. Figure 1 shows the spatial patterns of July to September (JAS) 2010 standardized anomalies of Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI) in vegetated areas of drought. The drought affected region, as depicted by the spatial patterns of JAS 2010 standardized anomalies of precipitation, is shown in Figure 2.
Figure 1: Spatial patterns of July to September (JAS) 2010 standardized anomalies of Normalized Difference Vegetation Index (NDVI) and Enhanced
Vegetation Index (EVI) in vegetated areas of drought (precipitation anomalies less than -1 standard deviation)
Figure 2: Spatial patterns of July to September (JAS) 2010 standardized anomalies of precipitation. Monthly precipitation rate (mm/hr) at a spatial resolution of 0.25degx0.25deg from The Tropical Rainfall Measuring Mission (TRMM) sensor is utilized for this study.
This project creates a platform to investigate the sensitivity of these Amazonian rain forests to extreme climatic anomalies (e.g. drought of 2005 and 2010), utilizing satellite-derived greenness data sets from MODIS on board the TERRA and AQUA sensor. Other ancillary data sets like precipitation and radiation are obtained from the TRMM and CERES sensors.
Collaborative research groups:
1. The Climate and Vegetation Research Group at Boston University, Boston, MA, USA.
2. Ecological Forecasting Lab at NASA Ames Research Center, Moffett Field, CA, USA.
3. Research Group on Biosphere-Atmosphere Interaction at the Federal University of Viçosa, Brazil.
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