Variabilidade temporal da concentração de metano e relação com o uso da terra no nordeste da Amazônia
Arquivos
Data
2023-12-13
Autores
Viana, Laura de Almeida 
Orientadores
Rizzo, Luciana Varanda
Tipo
Trabalho de conclusão de curso
Título da Revista
ISSN da Revista
Título de Volume
Resumo
O metano (CH4) é considerado o segundo gás do efeito estufa mais importante, perdendo apenas para o vapor d’água. Estudos mostram que o nordeste da Amazônia apresenta altas emissões de CH4 na Bacia Amazônica, região que passou por diversas transformações resultantes da construção da Rodovia Transamazônica e da Usina Hidrelétrica de Belo Monte. O objetivo deste trabalho de conclusão de curso é caracterizar a variabilidade temporal das concentrações de CH4 no nordeste da Amazônia entre 2003 e 2019, investigando associações com mudanças no uso da terra, variáveis meteorológicas e focos de queimadas. Para isso, foram utilizados dados diários de razão de mistura do CH4 na média troposfera (400 hPa) obtida pelo sensor AIRS/Aqua, além de dados de uso da terra, de reanálise de temperatura e precipitação (ERA5) e de focos de queimada. O conjunto de dados foi processado, gerando séries temporais médias e acumuladas das variáveis na área de estudo. Também foram obtidas trajetórias de massa de ar através do modelo Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) para investigar gradientes de concentração de CH4 dentro e fora da área de interesse. As análises estatísticas e de regressão multilinear do conjunto de dados foram feitas através do RStudio. As análises revelaram clara tendência de aumento das concentrações de CH4 na área de estudo, apresentando crescimento médio de 4,3±0,3 ppb/ano e R²=0,94. As concentrações também exibiram um padrão sazonal, sendo mais elevadas na estação seca (com uma tendência de 4,9±0,3 ppb/ano) e menores na estação chuvosa (com uma tendência de 3,8±0,3 ppb/ano), ambas com R²~0,90. Comparativamente, as concentrações de CH4 nas estações de background global da Ilha de Ascensão (ASC) e Barbados (RPB) foram maiores do que na área de estudo, com ASC e RPB apresentando tendências de 5,3±0,3 ppb/ano e 6,3±0,4 ppb/ano, respectivamente, ambos com R²=0,94. Foram observadas correlações estatisticamente significativas das concentrações de CH4 com a temperatura máxima diária (correlação positiva) e com a precipitação (correlação negativa). A redução na cobertura de floresta de 84% para 79% representou uma anti-correlação significativa com o CH4 na média troposfera. O modelo de regressão multilinear com dados anuais foi o que melhor representou as observações, enquanto que o modelo obtido com dados diários, apesar de representar bem a componente sazonal de concentração, não foi capaz de representar a tendência de longo. A série temporal de CH4 em ASC foi o preditor mais importante no modelo, sugerindo que a variabilidade de longo prazo de CH4 no nordeste da Amazônia foi majoritariamente influenciada por fatores globais. Acompanhando o caminho típico das massas de ar em março e setembro, à altura de 500 m, observou-se maiores concentrações de CH4 no Oceano em comparação com a área de estudo. Já na altura de 7000 m, nível aproximado das observações de CH4, não foi observado um claro gradiente de concentração na direção das trajetórias. Os resultados sugerem que a floresta pode estar atuando como sumidouro de carbono, apesar de que mais estudos são cruciais para aprofundar a compreensão de sua dinâmica global, tanto na superfície quanto na troposfera.
Methane (CH4) is considered the second most important greenhouse gas, second only to water vapor. Studies show that the northeastern part of the Amazon presents high CH4 emissions in the Amazon Basin, a region that has undergone various transformations due to the construction of the Trans-Amazon Highway and the Belo Monte Hydroelectric Power Plant. The aim of this final paper is to characterize the temporal variability of CH4 concentrations in the northeastern Amazon between 2003 and 2019, investigating associations with land use changes, meteorological variables, and fire incidents. Daily CH4 mixing ratio data in the average troposphere (400 hPa) obtained by the AIRS/Aqua sensor were used, along with land use data, temperature and precipitation reanalysis data (ERA5), and fire incident data. The dataset was processed, generating average and cumulative time series of variables in the study area. Air mass trajectories were also obtained using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model to investigate CH4 concentration gradients within and outside the area of interest. Statistical and multilinear regression analyses of the dataset were performed using RStudio. The analyses revealed a clear increasing trend in CH4 concentrations in the study area, with an average growth of 4.3±0.3 ppb/year and R²=0.94. Concentrations also exhibited a seasonal pattern, being higher in the dry season (with a trend of 4.9±0.3 ppb/year) and lower in the rainy season (with a trend of 3.8±0.3 ppb/year), both with R²~0.90. Comparatively, CH4 concentrations at the global background stations on Ascension Island (ASC) and Barbados (RPB) were higher than in the study area, with ASC and RPB showing trends of 5.3±0.3 ppb/year and 6.3±0.4 ppb/year, respectively, both with R²=0.94. Statistically significant correlations were observed between CH4 concentrations and daily maximum temperature (positive correlation) and precipitation (negative correlation). The reduction in forest cover from 84% to 79% represented a significant anti-correlation with CH4 in the average troposphere. The multilinear regression model with annual data best represented the observations, while the model obtained with daily data, despite capturing the seasonal concentration component well, failed to represent the long-term trend. The CH4 time series in ASC was the most important predictor in the model, suggesting that the long-term variability of CH4 in the northeastern Amazon was mainly influenced by global factors. Following the typical path of air masses in March and September, at an altitude of 500 m, higher CH4 concentrations were observed in the ocean compared to the study area. However, at an altitude of 7000 m, the approximate level of CH4 observations, a clear concentration gradient in the direction of trajectories was not observed. The results suggest that the forest may be acting as a carbon sink, although more studies are crucial to deepen the understanding of its global dynamics, both at the surface and in the troposphere.
Methane (CH4) is considered the second most important greenhouse gas, second only to water vapor. Studies show that the northeastern part of the Amazon presents high CH4 emissions in the Amazon Basin, a region that has undergone various transformations due to the construction of the Trans-Amazon Highway and the Belo Monte Hydroelectric Power Plant. The aim of this final paper is to characterize the temporal variability of CH4 concentrations in the northeastern Amazon between 2003 and 2019, investigating associations with land use changes, meteorological variables, and fire incidents. Daily CH4 mixing ratio data in the average troposphere (400 hPa) obtained by the AIRS/Aqua sensor were used, along with land use data, temperature and precipitation reanalysis data (ERA5), and fire incident data. The dataset was processed, generating average and cumulative time series of variables in the study area. Air mass trajectories were also obtained using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model to investigate CH4 concentration gradients within and outside the area of interest. Statistical and multilinear regression analyses of the dataset were performed using RStudio. The analyses revealed a clear increasing trend in CH4 concentrations in the study area, with an average growth of 4.3±0.3 ppb/year and R²=0.94. Concentrations also exhibited a seasonal pattern, being higher in the dry season (with a trend of 4.9±0.3 ppb/year) and lower in the rainy season (with a trend of 3.8±0.3 ppb/year), both with R²~0.90. Comparatively, CH4 concentrations at the global background stations on Ascension Island (ASC) and Barbados (RPB) were higher than in the study area, with ASC and RPB showing trends of 5.3±0.3 ppb/year and 6.3±0.4 ppb/year, respectively, both with R²=0.94. Statistically significant correlations were observed between CH4 concentrations and daily maximum temperature (positive correlation) and precipitation (negative correlation). The reduction in forest cover from 84% to 79% represented a significant anti-correlation with CH4 in the average troposphere. The multilinear regression model with annual data best represented the observations, while the model obtained with daily data, despite capturing the seasonal concentration component well, failed to represent the long-term trend. The CH4 time series in ASC was the most important predictor in the model, suggesting that the long-term variability of CH4 in the northeastern Amazon was mainly influenced by global factors. Following the typical path of air masses in March and September, at an altitude of 500 m, higher CH4 concentrations were observed in the ocean compared to the study area. However, at an altitude of 7000 m, the approximate level of CH4 observations, a clear concentration gradient in the direction of trajectories was not observed. The results suggest that the forest may be acting as a carbon sink, although more studies are crucial to deepen the understanding of its global dynamics, both at the surface and in the troposphere.