NeBIO_3-2-_Ningthoujam_17

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NeBIOVol. 3, No. 2, June 2012, 102-106

Author for correspondence

Ramesh K. NingthoujamEmail: [email protected]

NECEER, Imphal

Amazon Forest Greenness and MODISs Enhanced Vegetation Index

Ramesh K. Ningthoujam

Global Environmental Change and Earth Observation Research Group, Geography and Environment,

University of Southampton, UK..

ABSTRACT

Large and intact matured rainforest of Amazon experienced large seasonal

vegetation greenness by satellite MODIS EVI data during dry and wet seasons

including the 2005 drought highlighting different cues behind the greening of

EVI. An effort is made to reconcile the divergent views of the Amazon greening

through this brief article.

KEYWORDS: Amazon Rainforest, MODIS EVI, 2005 Drought.

The Amazon forest biome within the tropicalecosystem represents the biologically richest regionwith nearly 25% of global biodiversity, and is amajor contributor to the Earth system through

biogeochemical and biogeophysical processes (Malhiet al. 2008). This includes approximately 50% of theworlds undisturbed and matured intact rainforest

(FAO, 1992) with 10% terrestrial net primaryproductivity (Melillo et al. 1993), and a majorsurface evaporation process globally (Choudhury andDiGirolamo, 1998). Thus, relatively small changes or

shift in forest structure and dynamics in Amazon,therefore have the potential to substantially affect theenvironment regionally and globally and impacts ofclimate change itself (Phillips et al. 2009).

The Amazon region experienced an average annualair temperature of 26 C and 2400 mm (between>3000 mm in North West and


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Amazon Forest Greenness and MODISs Enhanced Vegetation Index Ningthoujam

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NeBIO I www.nebio.in I Vol. 3, No. 2, June 2012, 102-106 103

et al. 1998). Moreover, the sensitivity or resilience oftropical forests to drought could potentially reflectthe magnitude of the effects and feedbacks of thechanging ecology of Amazon forest in carbon cycle-climatic changes and may provide a proxy (evidence)for future climate conditions as predicted by some ofthe large-scale mathematical models (Cox et al.2008).

The MODIS Vegetation Indices (VI) products areprimarily designed to provide consistent, spatial andtemporal resolutions for monitoring vegetation

photosynthetic and seasonal phenology (Running etal. 1994). Of particular, two MODIS derived VInamely, Normalized Difference Vegetation Index(NDVI) and Enhanced Vegetation Index (EVI), are

produced at 5-km, 1-km and 500-m spatial and 16-day and monthly compositing periods globally. TheMODIS EVI defined as an algebraic manipulation ofvegetation reflectances at NIR, red and bluewavelengths with particular sensitivity to NIRreflectance (Huete et al. 2002). It is a measure ofvegetation greenness that generally correlates wellwith insitu photosynthesis and chlorophyll contentthrough a de-coupling of the canopy backgroundsignal and reduced atmospheric influences,

particularly useful in high biomass tropical forests

like the Amazon (Huete et al. 2006). Mathematically,EVI can be expressed as:

Figure 2.Spatial patterns of dry season greenness changesas depicted by EVI C5 (55 km2 spatial resolution) fromJune (EVIjun) to October (EVIoct) 2005 expressed as EVI(EVIoct - EVIjun) in the Amazon as similar to Huete et al.

(2006).

Not surprisingly, the EVI displays increased in thelate dry season compared to the wet season or earlydry season over the tropical forests of Amazon(Heute et al. 2006; Xiao et al. 2006; Saleska et al.2007; Brando et al. 2010) (see Figure 2). But whatdoes an increase in MODIS EVI mean to the remotesensing community? The large increased in EVI ofamazon forests particularly during the light-rich dryseason has been variously interpreted with a generalcharacterisation of a greening of amazon forestsduring dry season (Heute et al. 2006; Xiao et al.2006; Myneni et al. 2007; Brando et al. 2010). Thus,the aim of this article is to reconcile the divergentinterpretations of dry season greening of Amazonforests using MODIS EVI with special emphasis todrought in 2005.

By contrast, the climatological 2005 drought in intactAmazon forests showed a significant increase in theMODISs EVI C4 data, suggesting a possible higher

photosynthetic activity (greenness) as a result ofincreased solar radiation (due to reduced cloudiness)(Saleska et al. 2007). And moreover, this increasedEVI has been interpreted as closely coinciding withthe flushing of new leaves with seasonal peaks insolar irradiance (Saleska et al. 2003; Huete et al.2006). Thus, suggesting sunlight to be the main

climatic driver for the increased seasonal and leafflushing in the intact tropical forests during drymonths than rainfall at least in Amazonia (Wrightand van Schaik, 1994) and further, suggesting moreresilient in response to short-term climatic anomalies

particularly 2005 drought in Amazonia by these

intact forests than earlier thought; thus a large-scalegreening of Amazon forests during the 2005drought was emphasized (Saleska et al. 2007).However, this observation was challenged andinterpreted possibly due to atmospheric cloud

corruption and aerosol loadings from forest biomassburning using the improved version of EVI C5(Samanta et al. 2010), suggesting evidence of large-scale non- greening of Amazon forests during the2005 drought with lesser greening than in Saleska et

al. (2007). During the dry seasons and the drought of2005, a reduction in the moisture content ofvegetation was observed (Anderson et al. 2010);leading to increase leaf-shedding and drying leaveswith higher spread and frequency of forest fires

particularly in the drought-affected region. This

frequent drought-induced forest fires has beenregarded more likely to be the major driver of forest

EVI = 2.5

nir

red

nir

+ 6 red

7.5 blue

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