Pioneering study, focused on Central Amazonia, shows for the first time the seasonal and interannual variability of windthrows, occurring more frequently between September and February.
Windthrows are a recurring form of tree mortality in the Amazon and an important driver of forest dynamics and carbon storage. Our study shows that although windthrows occur all year long, they have a seasonal and interannual variability, occurring more frequently between September and February, driven by severe convective systems. Southerly squall lines have a higher frequency of occurrence and a greater effect on windthrows than previously reported. At the interannual scale, we did not find an association between ENSO and windthrows.
This study represents the first record of windthrow variability in the Amazon. Inclusion of windthrows in Earth System Models (ESMs) can help to reduce the uncertainties of climate prediction, given that windthrow-related tree mortality is not currently represented in ESMs.
Previous studies have shown that large windthrows in the Amazon are associated with squall lines, but whether the El Niño Southern Oscillation (ENSO) or seasonal rainfall are related to the occurrence of windthrows in the Amazon is unknown. In this study we present for the first time the seasonal and interannual variability of windthrows, focusing on Central Amazonia, and discuss the potential meteorological factors associated with this variability. Landsat images over the 1998-2010 time period were used to detect the occurrence of windthrows, which were identified based on their spectral characteristics and shape. Meteorological data were used to investigate the causes of windthrows. We found that windthrows occurred every year but were more frequent between September and February. Organized convective activity associated with multicell storms embedded in mesoscale convective systems, such as northerly squall lines (that move from northeast to southwest) and southerly squall lines (that move from southwest to northeast) can cause windthrows. We also found that southerly squall lines occurred more frequently than their previously reported ~50 year interval. At the interannual scale, we did not find an association between ENSO and windthrows.
Lawrence Berkeley National Laboratory
Negron-Juarez, R.I., H. S. Jenkins, C. F. M. Raupp, W. J. Riley, L. M. Kueppers, D. Magnabosco Marra, G. H. P. Ribeiro, M. T. Monterio, L. A. Candido, J. Q. Chambers, N. Higuch (2017). Windthrow Variability in Central Amazonia. Atmosphere, 8(2), 28, doi:10.3390/atmos8020028