Detecting Climate Change Concurrent with Deforestation in the Amazon Basin: Which Way Has It Gone?

Pao-Shin Chu
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Zhi-Ping Yu
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Stefan Hastenrath
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To detect climate change in the Amazon Basin, as possibly induced by deforestation, time series of monthly mean outgoing longwave radiation (OLR), an index of tropical convection, and monthly rainfall totals at Belem and Manaus for the past 15 years are analyzed. A systematic bias in the original OLR series was removed prior to the analysis. Linear regression analysis and nonlinear Mann-Kendall rank statistic are employed to detect trends. Over almost all of the basin, the OLR trend values are negative, indicating an increase of convection with time. The largest negative and statistically significant values are found in the western equatorial portion of Amazonia, where rainfall is most abundant. Consistent with this, the rainfall series at Belém and Manaus also feature upward trends. Small positive and statistically insignificant, OLR trend values are confined to the southern fringe of the basin, where deforestation has been most drastic. Thus, there is little indication for a rainfall increase associated with deforestation, but rather a strong signal of enhanced convection in the portion of Amazonia contributing most strongly to the total precipitation over the basin.

*Department of Meteorology, School of Ocean and Earth Science and Technology, University of Hawaii, Manoa, Hawaii.

+Department of Atmospheric and Oceanic Sciences, University of Wisconsin—Madison, Madison, Wisconsin.

Corresponding author address: Dr Pao-Shin Chu, Dept. of Meteorology, School of Ocean and Earth Science and Technology, 2525 Correa Rd., HIG 331, Honolulu, HI 96822.

To detect climate change in the Amazon Basin, as possibly induced by deforestation, time series of monthly mean outgoing longwave radiation (OLR), an index of tropical convection, and monthly rainfall totals at Belem and Manaus for the past 15 years are analyzed. A systematic bias in the original OLR series was removed prior to the analysis. Linear regression analysis and nonlinear Mann-Kendall rank statistic are employed to detect trends. Over almost all of the basin, the OLR trend values are negative, indicating an increase of convection with time. The largest negative and statistically significant values are found in the western equatorial portion of Amazonia, where rainfall is most abundant. Consistent with this, the rainfall series at Belém and Manaus also feature upward trends. Small positive and statistically insignificant, OLR trend values are confined to the southern fringe of the basin, where deforestation has been most drastic. Thus, there is little indication for a rainfall increase associated with deforestation, but rather a strong signal of enhanced convection in the portion of Amazonia contributing most strongly to the total precipitation over the basin.

*Department of Meteorology, School of Ocean and Earth Science and Technology, University of Hawaii, Manoa, Hawaii.

+Department of Atmospheric and Oceanic Sciences, University of Wisconsin—Madison, Madison, Wisconsin.

Corresponding author address: Dr Pao-Shin Chu, Dept. of Meteorology, School of Ocean and Earth Science and Technology, 2525 Correa Rd., HIG 331, Honolulu, HI 96822.
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