The Effect of Drought on Dust Storm Frequency (Case study: Bushehr Province)

Drought and dust are serious atmospheric hazards that have affected the western and southwestern parts of Iran in recent years due to various reasons. Since numerous droughts have had a detectable impact on occurrence and severity of dust, therefore, related studies are considered important. The purpose of this study is to analysis the trend of dust storms frequency and its relationship with drought (SPEI).

Bushehr province is located in ​​ north of the Persian Gulf and southwest of Iran. To investigate the effect of drought on dust storm, data on the dust events at daily timescale, monthly precipitation, temperature, humidity-relative, evapotranspiration data were utilized from 7 synoptic stations over 30 years (1989–2018).The Standardized Precipitation  Evapotranspiration Index (SPEI), dust storm occurrence based on weather codes 06 and 07 events and linear regression of parametric statistical test were used to estimate of drought, dust storm index (DSI) and their trends were analyzed by parametric linear regression test method. Spatial distribution of drought and dust in the case study obtained in Arc GIS software by IDW method. To investigate the relationship between climate and dust storms, the data of stations with significant trend of drought and dust storms frequency were analyzed using linear regression.   

The results showed that the percentage of drought frequency were classified into mild drought (79.06%), moderate drought (18.96%) and severe drought (2%) in the whole 30 years. Approximately 6.25% of droughts is occurred in the first decade, 50% in the second decade and 43.75% in the third decade. The spatial distribution map of drought also showed that the main focus of this phenomenon is occurred in the southern, central and northeastern parts of Bushehr province than rest of other parts. Existence air currents from Arabian Desert towards the central area of the province, the lack of appropriate vegetation, soil erosion and sand and salt zones in these parts have confirmed this issue. The percentage of occurrence of different drought during the whole study period showed that the occurrence of mild droughts was more than moderate droughts and the occurrence of moderate droughts was more than severe droughts. The overall trend of DSI changes across the entire study duration was decreased.

This study showed that dust storm index with increasing drought intensity was decreased and its correlation with drought during the 30-year period was not significant. Overlaying both of spatial distribution maps of drought and DSI did not show homogenous distribution pattern. This indicates that human factors or external source of dust can play a more important role in creating heterogeneous distribution pattern of drought and DSI in Bushehr province. Finally, the relationship between drought and DSI has always fluctuated according to dry and wet years over the whole study period.