Comment on bg-2021-173

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.