Abstract
Climate change and human activities have significant impacts on terrestrial vegetation. Syria is a typical arid region with a water-limited ecosystem and has experienced severe social unrest over the last decades. In this study, changes in vegetation and potential drivers in Syria are investigated. By using an enhanced vegetation index (EVI), a general browning trend is found in Syria during 2001–2018 with the EVI decreasing at a rate of −0.8 × 10−3 yr−1 (p < 0.1). The decrease of the EVI is mainly found in the north region, whereas the west region still maintains an increasing trend. The residual analysis indicates that besides precipitation, human activities also contribute significantly to the EVI decrease, which is confirmed by the decrease in rainfall use efficiency. In order to reach a more reliable conclusion, a comparative analysis is carried out in the Khabur River Basin where croplands are widely distributed in adjacent regions of Syria and Turkey. The time series of the EVIs over these two regions are highly correlated (r = 0.8027, p < 0.001), indicating that both regions are affected by similar climate forcing. However, vegetation in Syria and Turkey illustrates contrary browning (−3 × 10−3 yr−1, p < 0.01) and greening trends (4.5 × 10−3 yr−1, p < 0.01), respectively. Relative reports have reported that social unrest had induced insufficient irrigation and lack of seeds, fertilizers, pesticides and field managements. Therefore, we concluded that the decline of vegetation in the north Syria is driven by the change of land managements.
Highlights
By using an enhanced vegetation index (EVI), a general browning trend is found in Syria during 2001–2018 with the EVI decreasing at a rate of −0.8×10−3 yr−1 (p < 0.1)
Indexes such as the normalized difference vegetation index (NDVI) developed by the Global Inventory Monitoring and Modeling Studies (GIMMS), the enhanced vegetation index (EVI) product based on the Moderate Resolution Imaging Spectroradiometer (MODIS) and the leaf area index (LAI)
The accumulative remote sensing vegetation index can well represent the aboveground net primary productivity (ANPP). 125 Changes in the rainfall use efficiency (RUE) may be attributed to the factors other than water conditions, which can be generally considered as the influence of human activities (Leroux et al, 2017)
Summary
Vegetation is a key component of the Earth system and plays an important role in the water and energy cycle. It is one of the basic natural conditions for human survival. Recent advances in remote sensing technology and the establishment of long-term vegetation indexes have greatly facilitated the research on the long-term monitoring of large-scale vegetation. Indexes such as the normalized difference vegetation index (NDVI) developed by the Global Inventory Monitoring and Modeling Studies (GIMMS), the enhanced vegetation index (EVI) product based on the Moderate Resolution Imaging Spectroradiometer (MODIS) and the leaf area index (LAI)
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