Assessment of Caatinga response to drought using Meteosat-SEVIRI Normalized Difference Vegetation Index (2008-2016)

摘要

The Caatinga semi-arid vegetation in Northeast region of Brazil (NEB) provides a unique opportunity for studying the vegetation in response to recurring droughts, because of its negative impacts on soil erosion. Surprisingly, however, the response of Caatinga vegetation to a recent multi-year drought across the entire semi-arid NEB has not been studied in detail. This study analyses the spatiotemporal patterns of drought impact on the Caatinga vegetation between 2008 and 2016. Yet previous research has shown that a linear relationship exists between rainfall and Caatinga vegetation at interannual timescale. Because of the strong large-scale control of precipitation, year-to-year rainfall variations have a notable degree of spatiotemporal heterogeneity in semi-arid NEB. We exploit this relationship by developing the local-to regional-scale rainfall-Normalized Difference Vegetation Index (NDVI) distribution over the Caatinga vegetation, using daily rainfall time series from in situ weather stations, and daily Meteosat Second Generation (MSG) NDVI time series. Results showed that the drought impact (2012-2015) through the rainfall deficit dynamics influenced the dynamics of vegetative drought in the Caatinga vegetation where exhibit a strong decrease in vegetation activity, contrasting with irrigated croplands that exhibit little sensitivity to drought. It is the longest, continuous drought on the historical record (1901 onwards). The severe drought year of 2012 affected more than 26% of the vegetated area in the region. Over the 2012-2016 period, the positive trend observed in vegetation greenness is largely explained by a positive trend in the rainfall over 45% of the Caatinga vegetation, with the three months lagged rainfall (R-2 = 0.62 with p 0.05). This suggests that the vegetation greenness occurs in some portions of Caatinga region is mainly due to inadequate land management practices (i.e., irrigation with poor drainage, crop planting, bush encroachment, grazing-converted, pasture, etc.) often in combination with recurring droughts.