چكيده لاتين :
1. Introduction
The effect of climate of the Earth 's surface is the result of interaction of different levels of atmosphere and lithosphere. One of the factors which influences that interaction is the way the system pressure transcends it. In this way, the system pressure changes and can be changed and eventually may become an environmental hazard and geomorphodynamic phenomenon. Hazards are an integral part of human societies. Landslide hazards are considered as important Iranian geomorphclimatic hazards that every year brings a lot of damage to different areas. In the area study, the northern Alborz and Zagros Northwest, precipitation system paths have effective roles due to surface characteristics to create the landslides in the period from 14 to 31 March, 1998. The purpose of this study is tracking synoptic patterns conducive to landslides in the area study from 14 to 31 March 1998, to provide guidance for applied anticipations. The important low-pressure systems have entered in the study area from the routes:
-North Europe-Black Sea- East Mediterranean
- North Africa (Libya) - South Mediterranean -East Mediterranean
- East Mediterranean -North Iraq-Caspian Sea
- West Mediterranean- East Mediterranean -the Caspian Sea
- North Africa (Sudan) - Saudi Arabia - Persian Gulf.
2. Study Area
Due to the occurrence of landslides in the northern and western of Iran, the study area selected is the northern Alborz and Zagros northwest. Northern Alborz and Zagros northwest coordinate 30 to 40 degrees north latitude and 42 to 55 degrees east longitude (Figure 1).
3. Material and Methods
The study is based on analysis of terrestrial and atmospheric data. The general research approach is synoptic analysis based on the outputs of the Grads software and matching with the data recorded in the land stations Analytical and quantitative methods were performed by using statistical and geo-statistical software GIS and Excel. The database was created base on landslide database Iran Watershed Management Department under the Ministry of Agriculture, data of Iran meteorology organization and data from National Center Environmental Prediction (NCEP). The geographic coordinate of landslides, kind of landslides, occurrence date is extracted from the landslide database of Iran. The daily precipitation data are extracted from Iran meteorology organization. The rain, surface level pressure, geopotential height, specific humidity, zonal and meridian winds are extracted from the National Center Environmental Prediction. (Figure 2).
Figure 2. Diagram of research
4. Results and Discussion
74 landslides have occurred during 14-31 March 1998. The landslides occurred on Zagros and Alborz mountain ranges (Landslide Investigation Group, 2005). This area contains Ardabil, Charmahal va Bakhtiary, Khorasan Shomali, Kordastan, Kerman, Golestan, Gilan, Lorestan, Mazandaran and Hamedan provinces. Several factors contributed to the occurrence of landslides. In the north range of Alborz, most rain systems have received the moisture from the Caspian Sea. Winds while passing from the sea when they reach the shore are unstable and moist. Current water erosion is the dominant cause of the Alborz range. Northwest Zagros has heavy precipitation due to being in the flow path of the west winds. Landslide phenomena are abundant in Zagros and Alborz. Asmari, and Pabdeh, Gurpi, Shemshak formation with inter bedding, marl, shale and limestone and quaternary deposits are prone to landslides (Nikandish, (2001). Evaluation of precipitation data of 38 synoptic stations shows that slopes ' instability is the result of the two periods of precipitation which are separated by a pause of several days (Nikandish.2015). The spatial distribution of cumulative rainfall will reveal that the Zagros highlands role is strongly positive in receiving rainfall. Rain distribution on the North Alborz is more regular throughout the year. Significant proportion of the annual precipitation in the northwestern Zagros falls in short time which could cause flooding or landslides. The first rain has continued from March 14 to 18, 1998.The paths of causing precipitation systems during the first rainfall include: path 1 is Northern Europe - Black Sea - East Mediterranean, path 2 is North Africa (Libya) - Southeast Mediterranean - East Mediterranean, path 3 is East Mediterranean - North Iraq - Caspian Sea, path 4 is Northeastern of Iran – Uzbekistan. High pressures paths are located on the Kara Sea Route - Siberia and the Arabian Sea. Surface low pressure systems are controlled by a trough in 500 hpa. Apart from the southern east, Iran was located in the area of positive vorticity on March 18. The base on moisture and wind maps, Mediterranean Sea, Red Sea, Persian Gulf and Arabian Sea are water sources in the surface and 500 Hpa especially on 16- 18 March. Period of several days without rainfall continued in most stations from March 19 to 23. The loss of climbing mechanism and stopping the rain, intensified and accelerated the penetration of rainwater and snowmelt water, prepare the background for slope instability. Second precipitation has continued from 24 to 31 March 1998. General paths of precipitation systems include path 1 West Mediterranean - East Mediterranean – Caspian Sea, path 2 North Africa (Sudan) - Saudi Arabia - Persian Gulf, the path 3 Azerbaijan - Caspian Sea - Armenia and paths of high pressure are located on the Baltic Sea - Poland - Russia and the Arabian sea.
5. Conclusion
Through the process of locating emergency accommodation in the area, we came to the following conclusions. According to the environment criteria, earthquake (weight: 569/0) and landslide (weight: 228/0) have higher priority coefficient in locating. This means that villages that are suitable for locating temporary housing are away from environmental hazards. In general, only the village of Mayvan takes the highest scores for the physical location of temporary housing. In addition, the villages of Se Gonbad, Bash Mahale, Kharagh, and Yenge Ghale are placed at the next level benefiting from good conditions, whereas 26 villages under the study are not appropriate in terms of physical facilities and are thus not suitable to locate as temporary housing
base.
