Abstract
The spatio-temporal variability of trends in vegetation greenness in dryland areas is a well-documented phenomenon in remote sensing studies at global to regional scales. The underlying causes differ, however, and are often not well understood. Here, we analyzed the trends in vegetation greenness for a semi-arid area in northeastern Brazil (NEB) and examined the relationships between those dynamics and climate anomalies, namely the El Nino Southern Oscillation (ENSO) for the period 1982 to 2010, based on annual Normalized Difference Vegetation Index (NDVI) values from the latest version of the Global Inventory Modeling and Mapping Studies (GIMMS) NDVI dataset (NDVI3g) dataset. Against the ample assumption of ecological and socio-economic research, the results of our inter-annual trend analysis of NDVI and precipitation indicate large areas of significant greening in the observation period. The spatial extent and strength of greening is a function of the prevalent land-cover type or biome in the study area. The regression analysis of ENSO indicators and NDVI anomalies reveals a close relation of ENSO warm events and periods of reduced vegetation greenness, with a temporal lag of 12 months. The spatial patterns of this relation vary in space and time. Thus, not every ENSO warm event is reflected in negative NDVI anomalies. Xeric shrublands (Caatinga) are more sensitive to ENSO teleconnections than other biomes in the study area.
Highlights
Northeastern Brazil (NEB) is characterized by a semi-arid climate, high intra-annual and inter-annual variability of rainfall and, vegetation productivity [1,2,3,4]
The inter-annual trend analysis of the NDVI3g time series from 1982 to 2010 for NEB reveals a spatial heterogeneity of long-term greening and browning in the study area
Significant trends were observed for 43% of the study area, with the vast majority of trends relating to vegetation greening
Summary
Northeastern Brazil (NEB) is characterized by a semi-arid climate, high intra-annual and inter-annual variability of rainfall and, vegetation productivity [1,2,3,4]. Using Normalized Difference Vegetation Index (NDVI) time series, Barbosa et al [1] and Schucknecht et al [2] reported significant variability in vegetation greenness, for the semi-arid northeastern part of Brazil. The NDVI, computed from time series of medium- to coarse-resolution satellite data, is widely accepted as a proxy for vegetation greenness [17,18]. It provides a gross measure of vegetation productivity despite recently discovered restrictions, due to species composition and seasonal cycles [19]. Vegetation greenness in semi-arid regions is causally linked to precipitation occurrence and temporal variation
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