Forecasting occur probability intense storm using Gumbel distribution; Case study: Nahavand township

Natural disasters such as storm are not tangible that allocate about 30% share of 90% of natural disasters. This study aimed to forecast occur probability of intense storms using Gambel distribution in Nahavand township based on 10 years, period from 1996 to 2005. Nahavand due to climatic characteristics and topography is an area stormy in Hamedan province and base on Nahavand station include the most occur storms in 2003 and 2004. In this study, Rainfall zoning of Hamedan province was done by geo statistic based on average rainfall 33 stations in Hamedan province and 10 stations from neighboring provinces. For indicating average speed and aspect of wind was used Wind rose. Using Wind rose software designed wind rose of autumn and winter moreover. Gambel distribution was used for study statistically and predicting the incident probability of stormy and strong winds in Nahavand. To select days along with stormy and strong wind, winds with equal speed and more than 17 m/s and accepted by the Weather Meteorology Organization (WMO) are accounted as days by a stormy and strong wind. Also, applied types of distribution using Smada software which best fit was for the Gumbel distribution. Based on the Beaufort index in a return period of 5 years, with a speed of 26 m/s and more there is likely to storm in the station of Nahavand. On the other hand, the maximum of thunderstorms of Hamedan province occurred in Nahavand station and most number of them is in the spring season. If the storm continued causing great damage to agriculture, services, electricity and telephone lines, trees, and gardens, etc. Thus, for the environmental planning and safety of structures must consider the occurrence of this natural danger to decrease these disturbing effects.