Spatial and seasonal variations of sand-dust events and their relation to atmospheric conditions and vegetation cover in semi-arid regions of central Iran

摘要

Atmospheric conditions and physical characteristics of the earth surface have an important effect on the spatiotemporal variations of sand-dust events. The main objective of the present study was to investigate the effect of these variables on the seasonal variation of these events in semi-arid regions of Central Iran Zone (CIZ). The Ridge Regression (RR) method was used to analyze the relationship between seasonal variations of precipitation, surface winds speed, air temperature, and Enhanced Vegetation Index (EVI) with Dust Storm Index (DSI) for two different periods (2001-2008 and 2009-2016). The dusty winds direction around the study area was also determined using the dust roses. The results showed that the annual DSI changes in the study area had a week incremental trend with a rate of 0.07/8 yrs in the previous period while it followed a strong increasing trend with a rate of 0.22/8 yrs in the latter period. It was also found that the activity of sand-dust storms in the second period was greater than the first period, especially in the border region of Iran and Turkmenistan. According to RR analysis, DSI had a significant positive association with the surface winds speed in the summer (beta = +0.48; p-value < 0.05) and the winter precipitation (beta = 0.3; p-value < 0.05) over the previous period. During this period, there was no significant relationship between the temperature and EVI with DSI in other seasons (pvalue > 0.05). In the second period, the surface winds speed was positively correlated with the DSI in the spring beta = + 2.04), summer (beta = + 2.6) and autumn (beta = + 2.08). The significant negative relationship between EVI and DSI changes was observed only in the spring season (beta = 0.7; p-value < 0.05). Our findings also indicated that dusty winds direction in the northeast, northwest, and southeast parts of the study area were from the northwest, southeast, and west, respectively. These findings can help to mitigate the negative consequences of dust emissions and improve the wind erosion management in semi-dry lands of CIZ.