Spatial and Temporal Patterns of Amazon Rainfall

Sombroek, W.G.

doi:10.1639/0044-7447(2001)030[0388:satpoa]2.0.co;2

Cited by 91 publications

(96 citation statements)

References 23 publications

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“…2B). Second, the homogeneous region roughly overlies the precipitation gradient (20) in the basin (see SI Materials and Methods and SI Fig. 4C), suggesting that the amplitude is, to a first approximation, independent of the duration and intensity of the dry season.…”

Section: Seasonality In Lai Timementioning

confidence: 93%

Large seasonal swings in leaf area of Amazon rainforests

Myneni

Yang

Nemani

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

389

367

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Despite early speculation to the contrary, all tropical forests studied to date display seasonal variations in the presence of new leaves, flowers, and fruits. Past studies were focused on the timing of phenological events and their cues but not on the accompanying changes in leaf area that regulate vegetation-atmosphere exchanges of energy, momentum, and mass. Here we report, from analysis of 5 years of recent satellite data, seasonal swings in green leaf area of Ϸ25% in a majority of the Amazon rainforests. This seasonal cycle is timed to the seasonality of solar radiation in a manner that is suggestive of anticipatory and opportunistic patterns of net leaf flushing during the early to mid part of the light-rich dry season and net leaf abscission during the cloudy wet season. These seasonal swings in leaf area may be critical to initiation of the transition from dry to wet season, seasonal carbon balance between photosynthetic gains and respiratory losses, and litterfall nutrient cycling in moist tropical forests.remote sensing ͉ tropical forests phenology ͉ vegetation climate interaction T he trees of tropical rainforests are known to exhibit a range of phenological behavior, from episodes of ephemeral leaf bursts followed by long quiescent periods to continuous leafing, and from complete intraspecific synchrony to complete asynchrony (1). Several agents (e.g., herbivory, water stress, day length, light intensity, mineral nutrition, and flood pulse) have been identified as proximate cues for leafing and abscission in these communities (1-8). These studies were focused on the timing of phenological events but not on the accompanying changes in leaf area. Leaves selectively absorb solar radiation, emit longwave radiation and volatile organic compounds, and facilitate growth by regulating carbon dioxide influx and water vapor efflux from stomates. Therefore, leaf area dynamics are relevant to studies of climatic, hydrological, and biogeochemical cycles.The sheer size and diversity of rainforests preclude a synoptic view of leaf area changes from ground sampling. We therefore used data on green leaf area of the Amazon basin (Ϸ7.2 ϫ 10 6 km 2 ) derived from measurements made by the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Na- Results Seasonality in LAI Time Series.Leaf area data for the Amazon rainforests exhibit notable seasonality, with an amplitude (peakto-trough difference) that is 25% of the average annual LAI of 4.7 (Fig. 1A). This average amplitude of 1.2 LAI is about twice the error of a single estimate of MODIS LAI, and thus is not an artifact of remote observation or data processing (see SI Materials and Methods). The aggregate phenological cycle appears timed to the seasonality of solar radiation in a manner that is suggestive of anticipatory and opportunistic patterns of leaf flushing and abscission. These patterns result in leaf area leading solar radiation during the entire seasonal cycle, with higher leaf area during the shorter dry season when solar radiation loads are hig...

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Section: Seasonality In Lai Timementioning

confidence: 93%

Large seasonal swings in leaf area of Amazon rainforests

Myneni

Yang

Nemani

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

389

367

View full text Add to dashboard Cite

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“…Areas of maximum precipitation (see also figure 1) had the lowest rate (,40%). These areas also show from zero to three consecutive months with precipitation ,100 mm and lower daylight intensity (Sombroek 2001). High precipitation implies high cloudiness, and therefore less radiation available to promote E T .…”

Section: E T /Precipitation Rates Over the Amazonmentioning

confidence: 97%

“…To study the capability of EVI to monitor the interannual variability of Amazon forest we performed an analysis over an area in the eastern Amazon (2u S-5u S, 53u W-56u W) that experiences regular droughts from El Niñ o events (Stokstad 2005). In this area, the dry season lasts 5 months (consecutive months with precipitation ,100 mm) centred in September (Sombroek 2001 (Shein 2006). In this year, after 6 months of wetter than normal precipitation conditions, a moderate drought event was observed in September.…”

Section: Sensitivity Of Evi To Climate Variabilitymentioning

confidence: 99%

“…E T /precipitation rates with values greater than 40% were observed in southern, eastern and middle areas of the basin. These areas are characterized by annual precipitation ,2000 mm (figure 1), 4-7 consecutive months of precipitation ,100 mm (Sombroek 2001) and low values of maximum PAW (Nepstad et al 2004), and their temperatures strongly correlated with the El Niñ o-Southern Oscillation (ENSO) index (Malhi and Wright 2004). As a result, these areas are more susceptible to drought events and fires.…”

Section: E T /Precipitation Rates Over the Amazonmentioning

confidence: 99%

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An empirical approach to retrieving monthly evapotranspiration over Amazonia

Juarez

Goulden

Myneni

et al. 2008

International Journal of Remote Sensing

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The extent of evapotranspiration (E T ) over the Brazilian Amazon rainforest remains uncertain because in situ measurement sites do not cover the entire domain, and the fetch of these sites is only of the order of 10 3 m. In this investigation we developed an empirical method to estimate E T over the Brazilian Legal Amazon (BLA). The work was based on an improved physical understanding of what controls E T over the Amazonia rainforest resulting from analyses of recent in situ observations. Satellite data used in this study include the Enhanced Vegetation Index (EVI) from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the surface radiation budget from the International Satellite Cloud Climatology Project (ISCCP). The empirical model was validated by measurements performed at four upland forest sites. The observed values and the calculated modelled values at these sites had the same mean and variance. On a seasonal scale, regional modelled E T peaks during the austral spring (September to November), as reported in the literature. In addition, the empirical model allows us to estimate the regional seasonal and interannual distributions of E T /precipitation rates.

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“…RAINFOR authors have also discounted El Niñ o events as a source of disturbance because two very strong events occurred during 1982-1983 and 1997-1998 after most tree plots were established [31,39]. The most severe regional drought coincided with the 1925-1926 El Niñ o event, however, when fires were widespread and the Amazon reached the lowest level yet recorded at Manaus [48,49]. More importantly, multiple sources of past disturbance need to be evaluated.…”

Section: The Evidence Questionedmentioning

confidence: 99%