Document Type : مقاله پژوهشی
Atmospheric hazards are defined as any atmospheric event, which adversely affect or may adversely affect human life, property, or other aspects of the environment. The events can influence all aspects of human life. The main purpose of this research is zonation of atmospheric hazards in the northeast of Iran including North Khorasan, Khorasan Razavi and South Khorasan. In order to achieve the purpose, the spatial distribution of all atmospheric hazards, which occur over the area, has been investigated in terms of frequency and intensity.
2. Study Area
Study Area is located in the northeastern of Iran with an area of 300000 Km between N30 21 to N38 17 latitudes and E55 28 to E61 14 Longitudes. The Study Area concludes three following provinces in the country: Khorasan Shomali, Khorasan Razavi and Khorasan Jonobi which have been separated from great Khorasan during the past decade. Extending the region from low latitudes to high latitudes and affected by different climatic systems resulted occurrence of a set climatic hazards throughout the study area. This paper is focused on atmospheric hazards zoning in the area using geographic information Systems (GIS).
3. Material and Methods
In order to identify the spatial distribution of each atmospheric hazard, the meteorological data of 17 weather stations in North Khorasan, Khorasan Razavi and South Khorasan is used for a 38-year (1971-2008) period. In this basis, 13 variables including precipitation, mean temperature, maximum temperature, minimum temperature, wind direction and intensity, visibility and weather conditions in terms of daily and monthly scales were used to investigate the frequency and the intensity of atmospheric hazards. In the first step, 13 major atmospheric hazards, including drought, heavy and extreme precipitation events, heavy snowfall, hail, thunderstorm, blizzard, fog, dust storm, dusty days, heat wave, frost and wind-chill events were identified in the scope of northeast of Iran. To make a general zonation map for atmospheric hazards, we analyzed each atmospheric hazard by a distinct method with regards to the characteristics of each hazard. Using the distinct methods, we determined the frequency and intensity of each hazard. Then, the Geography Information System (GIS) is applied to make a spatial analysis of the events and spatial distribution map is produced for each hazard by using ArcGIS tools. In the next step, all atmospheric hazards have been contained in three categories, with regards to their similarities and differences. Therefore, all atmospheric hazards categorized in temperature-based hazards, precipitation-related hazards and weather hazards related to visibility. As a final step, we combined all atmospheric hazards to make a general zonation map for the Northeast of Iran.
4. Results and Discussion
The results indicate that the freezing and wind-chill events are the most frequent hazards in the northeast of Iran. It is found that, while the temperature-based hazards are increasing from north to south, the spatial distribution of precipitation-related hazards is showing an inverse mode, so that they are increasing from south to north. In contrast, the spatial distribution of atmospheric hazards related to visibility is more zonal than meridian direction. Therefore, they are showing a decrease from east to west. The final zonation map of atmospheric hazards which produced by combination of all elements confirm that the more hazards in northern part of the study area can be caused by the high frequency of eastward movement of extra-tropical systems as well as high mountains arrangement in northeastern part of Iran.
The research showed that the north and northeastern parts of the study area hit by more atmospheric hazards and has the highest frequency of atmospheric hazards in regards to spatial analysis of the events. Therefore, we can conclude that the large parts of northern and northeastern Khorasan should be considered the most risky area over the whole domain. In contrast, the western and southern parts of Khorasan are the lowest risky areas as well. The results also indicate that the wind-chill event is the dominant atmospheric hazard over the entire domain in terms of frequency.