Impacts of vegetation anomalies and agricultural drought on wind erosion over Iran from 2000 to 2018

Abstract

Vegetation cover plays a key role in reducing wind erosion and improving air quality in different parts of the world. However, little is known about the long-term period seasonal changes in vegetation anomalies and their effects on wind erosion in Iran. Therefore, in the current research, the seasonal changes in vegetation cover and the level of wind erosion activity across the country from 2000 to 2018 have been identified in detail using the Normalized Difference Vegetation Index anomaly (NDVIA) and the dust concentration anomaly (DCA), respectively. Furthermore, the nonparametric Mann–Kendall test and Sen's slope estimator were used to evaluate the variable trend changes. The bivariate correlation analysis was performed to determine the relationship between NDVIA and DCA in the spring, summer, autumn, winter, and growing season. The agricultural drought was further monitored for the season when the strongest correlation between vegetation changes and the activity of wind erosion events was observed. The NDVIA and DCA maps were spatially analyzed to identify areas affected by drought and wind erosion, respectively. Results indicated that across the whole country, the NDVIA increased significantly in the autumn and growing season (Z>+2; α < 0.05) while the DCA had a significant decreasing trend in the spring and growing season (Z < -2.5; α < 0.05). The results of correlation analysis indicated that NDVIA corresponded well with the DCA in the spring (R = −0.58; P < 0.05), summer (R = −0.52; P < 0.05) and growing season (R = −0.67; P < 0.01) while no meaningful correlation was found between them in the winter and autumn (R<−0.25; P>0.05). Agricultural drought monitoring using the growing season NDVIA showed that about 85%, 72%, 67%, 63%, 62%, and 61% of Iran has experienced this phenomenon over the years 2008, 2000, 2018, 2002, 2006, and 2003, respectively. The DCA maps displayed more than 54% of the country has suffered from the intensification of the wind erosion over the years. Our findings also demonstrated that areas with NDVIA<0 have had a significant impact on dust produced by wind erosion in areas with DCA>0 (R = −0.5; P = 0.03). Spatially, these areas were mainly observed in the eastern half of Iran, areas that were most affected by the drought over the monitoring years. This work encourages us to use the NDVIA and DCA to evaluate the linkage between seasonal vegetation variations and wind erosion activity in arid and semi-arid regions. This study could also be useful for recognizing areas at risk of drought and wind erosion as well as for mitigating their adverse effects.