Tendências temporais de índices de vegetação nos campos do Pampa do Brasil e do Uruguai

Abstract

Resumo -O objetivo deste trabalho foi avaliar a redução do vigor vegetativo da cobertura vegetal do Pampa do Brasil e do Uruguai, por meio da identificação de tendências negativas em séries temporais de imagens. Utilizaram-se séries temporais de imagens de NDVI/EVI do sensor Modis, de 2000 a 2011; imagens de índices de umidade do solo do "climate forecast system reanalysis"; e dados de precipitação pluvial de estações meteorológicas. O estudo quantificou tendências lineares e não lineares nas séries de NDVI e EVI, em áreas de campos. Na tendência monotônica de Mann-Kendall, a 5% de probabilidade, 81,9% da área total estudada foi significativa com o NDVI, e 74,8%, com o EVI; no entanto, o EVI apresentou contraste superior na estimativa dos parâmetros. Os resultados mostraram maior sinal negativo a oeste, com valores médios de R 2 >0,15, r<-0,3 e τ <-0,15 na tendência dos índices de vegetação, e tendência decrescente para NDVI, EVI e precipitação pluvial, com menores valores médios de umidade do solo. A tendência negativa dos índices de vegetação, relacionada à combinação da ocorrência de deficit hídrico em solos rasos com o sobrepastoreio, indica alterações no padrão de cobertura vegetal do Pampa, com redução do vigor vegetativo.Termos para indexação: campos nativos, EVI, Modis, NDVI, séries temporais. Temporal trends of vegetation indices on Pampa grasslands in Brazil and UruguayAbstract -The objective of this work was to evaluate the reduction in the vegetative vigor of Pampa vegetation cover in Brazil and Uruguay, by identifying negative trends in images time series. The following were used: time series of NDVI/EVI images from the Modis sensor, from 2000 to 2011; images from soil moisture indices from the climate forecast system reanalysis; and precipitation data from meteorological stations. The study quantified linear and nonlinear trends in the NDVI and EVI series in grassland areas. With the MannKendall monotonic trend, at 5% probability, 81.9% of the total area studied was significant with NDVI, and 74.8% with EVI; however, EVI showed superior contrast in the estimation of parameters. The results showed: highest negative signal in the west, with average values of R 2 >0.15, r<-0.3, and τ <-0.15 in the tendency of the vegetation indices; and decreasing tendency for NDVI, EVI, and rainfall, with lower mean soil moisture values. The negative trend of the vegetation indices, related to the combination of drought occurrence in surface soils with excessive grazing, indicates changes in the pattern of Pampa vegetation cover, with reduction in vegetative vigor.

NDVI and meteorological data as indicators of the Pampa biome natural grasslands growth

“…In these situations, the water limitation in the soil leads to restricted resources for plant growth, which is insufficient (Rueda et al 2013). The effect of water deficit on the reduction of NDVI values during summer has already been described in similar studies in this region (Wagner et al 2013;Kuplich et al 2013), being characterized as the main adverse meteorological event at this season and, therefore, associated with agricultural losses (Berlato and Fontana 2003). During autumn, the NDVI values were also high and statistically similar to those observed in spring and summer ( Figure 2).…”

“…Therefore, VI shows potential to obtain inferences about growth and development of the vegetation in general (Soudani et al 2012). They also have had, in RS, a significant use in monitoring, either for annual agricultural crops (Junges et al 2013;Santos et al 2014;Mengue and Fontana 2015), for grasslands (Fonseca et al 2007;Soudani et al 2012;Wagner et al 2013;Scottá and Fonseca 2015;Junges et al 2016) or forests (Berra et al 2014).…”

Trend of Air Temperature in the State of Paraná, Brazil (Tendência Da Temperatura Do Ar No Estado Do Paraná, Brasil)

“…Kendall's tau statistics (Equation 3) was used to indicate the trend movement, as used in Li, Zhe et al (2013) and Wagner et al (2013). A positive tau value means an increasing trend while a negative value represents a decreasing trend.…”

Inferências sobre o calendário agrícola a partir de perfis temporais de NDVI/MODIS

“…Since the NDVI is significantly associated with green plant biomass (Jensen, 2009;Ponzoni & Shimabukuro, 2007), this has been the index most frequently used in studies on the behavior of vegetation. Of note is the use of NDVI from MODIS images in monitoring the development of crops (Jacóbsen et al, 2003;Junges & Fontana, 2009;Wagner et al, 2013), grain modeling (De Melo et al, 2008;Rizzi & Rudorff, 2007;Fontana et al, 2007;Mercante et al, 2010) and acreage estimation (Gusso et al, 2012;Johann et al, 2012;Santos et al, 2014).…”