# Regional Analysis of Dust Day Duration in Central Iran
## 3 Results
### Statistical Analysis of Dust Durability  
Statistical analysis in the period 1999-2018 shows that the highest duration of dust days in 2014 occurred in Zabol stations with 22 and Zahdan with 21 consecutive days. Additionally, in Zabol and Zahdan stations, the minimum annual-maximum duration of dust days is 11 and 9 days. The diagram of annual-maximum DDD in these two stations during the period 1999-2018 is shown in Figure 5.  
A seasonal survey of the index station of the region (Zabol and Zahdan stations) shows that the highest frequency of dust events occurs in summer, followed by spring; in particular, in Zahdan and Zabol stations about 52% and 48% of multiday dust storms occurred in summer; their diagrams are shown in Figure 6. The most important reasons for the high frequency of dusty days in this area in summer, include high temperatures that cause severe evaporation of water resources along with lack of rainfall in summer, all leading to reduced adhesion of soil particles due to lack of moisture. Dust emissions are worsened by the 120-day erosive winds of Sistan that blow in summer and strongly affect the eastern parts of Iran  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**D** & **LCk** & **LCv** & **LCs** & **Station Name** & **Station Number** \\ \hline
1.54 & 0.369 & 0.476 & 0.553 & Ferdoos & 29 \\ \hline
1.95 & 0.275 & 0.698 & 0.187 & Tabas & 30 \\ \hline
0.42 & 0.399 & 0.771 & 0.195 & Karaj & 31 \\ \hline
0.31 & 0.281 & 0.432 & 0.543 & Ghazvin & 32 \\ \hline
1.58 & 0.186 & 0.304 & 0.229 & Hashtgerd & 33 \\ \hline
0.01 & 0.168 & 0.454 & 0.304 & Abali & 34 \\ \hline
0.48 & 0.147 & 0.538 & 0.34 & Takestan & 35 \\ \hline  & \multicolumn{4}{c}{\(\mathbf{H_{1}=0.64}\)} \\  & \multicolumn{4}{c}{\(\mathbf{H_{2}=-0.07}\)} \\  & \multicolumn{4}{c}{\(\mathbf{H_{3}=-0.72}\)} \\ \hline \end{tabular}
\end{table}
Table 2: _Cont._  
Figure 5: Annual-maximum dust days duration in Zabol and Zahdan stations 1999–2018.  
After Zabol station with 22 days and Zahdan with 21 days, the next longest DDD was recorded at Anar, Nain, and Saveh stations with 8 days, as shown in Figure 7.  
There is a big difference between the DDD values of Zahdan and Zabol stations and other stations in the study area. Although stations in the central deserts of Iran such as Khor, Biabank, Yazd, and Semnan, also have favorable climatic and graphic conditions for wind erosion, the Zahdan and Zabol stations are the most affected by the 120-day winds of Sistan, known as the monsoon winds, that blow continuously over prolonged periods.  
Furthermore, regarding the average annual-maximum dust day duration in the study area, Zabol station with an average of 15 days and Zahdan station with an average of 14.3 days had the highest values over the study period. On the other hand, Hashtgerd and Semnan stations with 0.98 and 1.25 days, respectively, had the lowest values in the area (Figure 8).  
Figure 8: Graph of average dust day durations by station in the study area.  
Figure 6: Seasonal diagram of multiday dust events at Zabol and Zahdan station.  
Figure 7: Diagram of maximum DDD, 1999–2018, in the study area.  
Then, using GIS software and the kriging interpolation method, the maximum, minimum and average annual-maximum DDD over 1999-2018 were mapped in Figures 9-11, respectively.  
According to Figure 9, DDD is maximum in the east and southeast of the study area. Additionally, Saveh and Arak stations in the northwest of the region have a relatively high DDD.  
Figures 10 and 11, which are related to the maximum and minimum duration of annual-maximum DDD in the region, show that, the southeastern parts of the study area have the highest values of DDD for both the most and least dusty years, which indicates the difficult conditions of the area.