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PI-Submitted Research Highlights for
Terrestrial Ecosystem Science Program

Windthrow Variability in Central Amazonia

William J. Riley
Lawrence Berkeley National Lab


February 7, 2017
Windthrows occur every year

The Science
Windthrows (gaps of uprooted or broken trees) are a recurrent disturbance in Amazonia that affects the persistence of woody biomass, which, in turn, affects patterns of productivity and biomass, floristic composition, and soil composition in the basin. Windthrows are produced by severe convective events that are expected to be more frequent with climate change. Yet the variability of windthrows over time has not been investigated. Studying the frequency of windthrows occurrence is key to understanding the atmospheric conditions that produce these events. This understanding will also improve Earth System Models (ESM) representations, since windthrow related tree mortality is currently not included.

The Impact
Our results show that windthrows occur every year and were more frequent from September through February. One driver of windthrows are southerly squall lines (that form in southern Amazonia and move to northeast Amazonia) that we found to be more frequent than their previously reported ~50 year interval. Our results will improve representations of tree mortality in ESMs, and in particular the ACME Land Model (ALM).

Windthrows are a recurrent disturbance in Amazonia and are an important driver of forest dynamics and carbon storage. 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. 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 El Niño-Southern Oscillation (ENSO) and windthrows.

Contacts (BER PM)
Renu Joseph and Dan Stover
Renu.Joseph@science.doe.gov (301-903-9237) and Daniel.Stover@science.doe.gov (301-903-0289)

PI Contact
William J. Riley
Lawrence Berkeley National Lab

This research was supported as part of the Next Generation Ecosystem Experiments-Tropics project and the Regional and Global Climate Modeling program, both funded by the U.S. Department of Energy, Office of Science, and the Office of Biological and Environmental Research under contract DE-AC02-05CH11231.

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.

DOE National Laboratory (LBNL) as part of the NGEE-Tropics project (BER/TES) as well as the BGC-Feedbacks SFA (BER/RGCM).

Annual occurrence of windthrow events (solid and dashed lines) over hydrological years 1998–1999 to 2009–2010 plotted against annual rainfall (gray bars). Rainfall data taken from Tropical Rainfall Measuring Mission 3B43 (TRMMmo) as described in Section 2.2. Rainfall data and windthrows correspond to the area covered by the Landsat tile P231/R062 as described in Section 2.1. HY (Hydrological year) case plotted in the solid line and HYb plotted in the dashed line. La Niña years highlighted in blue, El Niño years highlighted in red.

From manuscript (figure 5) 

midsized version

The position of southerly squall lines in the Amazon at different times obtained using TRMM3h data. The Landsat tile of the study area is also shown. The numbers in the Figures (e.g., 6, 18 Z) indicate the last day of the month, and the hour (in Coordinate Universal Time, Z).

From manuscript (figure 6).

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