Analysis of the Wind Speed Trend over Iran

The aim of this study is the analysis of surface wind speed in monthly and annual times scales in Iran using four different versions of the Mann-Kendall i) conventional Mann-Kendall method (MK1); ii) Mann-Kendall method following removing the effect of significant lag-1 auto-correlation (MK2); iii) Mann-Kendall method after the removing the effect of all significant auto-correlation coefficients (MK3); and Mann-Kendall method with considering the Hurst coefficient (MK4). Data used here are wind speed records in both monthly and annual time scales in the period of 1966-2005. For this purpose، 22 stations were selected across Iran’s area. Nonparametric Sen’s method was used for estimation of wind trend line slope. Results showed that although a combination of positive and negative trends observed both in monthly and annual time scales، however، the number of stations having the negative trends were more than that of the positive trends. In the annual time scale، the strongest negative trend line slope was -0. 074 ms-1y-1 belonging to Fasa station، and the strongest positive trend line slope was 0. 141 ms-1y-1 belonging to Zabol station. In monthly time scale، the strongest negative trend line slope was -0. 1 ms-1y-1 observed in Fasa station and the the strongest positive trend line slope was 0. 18 ms-1y-1 observed in Zabol station. Results showed that the median of the trend line slopes for all months (except February and November) was negative. Therefore، in general، it can be concluded that in the most of stations in Iran wind speed trend in all months (except February and November) was negative.