پهنه بندي مخاطرات بارشي منجر به خشكسالي و سيل در حوضه هاي آبريز حله و مند

Zoning of Rain hazards of drought and flood emphasis on population centers in Helle and Mond basins

خطر، منشاء آسيب بالقوه يا موقعيتي براي ايجاد خسارت است، بنابراين شناسايي پهنه هاي مواجه با مخاطرات امري لازم براي برنامه ريزي محيطي يا آمايش سرزمين است. منظور از مخاطره، عموماً ويژگي هاي كالبدي است كه منجر به حوادث غير مترقبه مي شود.به عنوان مثال گسل هاي فعال، آتش فشان ها، مناطق سيل خير و اراضي مستعد اشتعال همگي جزو مخاطرات طبيعي هستند. لذا توجه به شرايط خطرپذيري مخاطرات اقليمي در مناطق مسكوني با توجه به جمعيت هاي شهري و روستايي لازمه برنامه ريزي محيطي مي باشد. با توجه به اين مهم در اين تحقيق نخست تلاش شده است تا با استفاده از آمار ايستگاه هاي باران سنجي و سينوپتيك حوضه هاي آبريز حله و مند طي يك دوره آماري 20 ساله (1371-1390)، شاخص خشكسالي SPI در منطقه مورد مطالعه محاسبه شود. سپس از لايه هاي رقومي پهنه هاي سيلابي، مجموع متوسط بارندگي و مجموع تبخير و تعرق سالانه براي ارزيابي پهنه هاي با خطر رخداد سيلاب استفاده شده است.در اين راستا از روش تحليل سلسله مراتبي (AHP) و منطق( Fuzzy)- مناطق با خطر رخداد پهنه هاي سيلاب و خشكسالي، و تبخير و تعرق سالانه در سطح منطقه مورد مطالعه، پهنه بندي و شناسايي شدند. با توجه به نقشه نهايي آسيب پذيري مشخص شد كه مناطق همجوار و خصوصا شهرهاي واقع در كنار سواحل خليج فارس در غرب،شمال غرب و جنوب حوضه هاي آبريز حله و مند داراي بيشترين آسيب پذيري بوده و مناطق شرق و شمال شرق منطقه مورد مطالعه و مراكز جمعيتي آنها، از كمترين آسيب پذيري برخوردار هستند.

Hazard is potential source of harm or a situation to create a damage. So identification of zones exposed to hazards is necessary for planning or land use planning. But this situation becomes more critical when they appear at the population centers. So applying the principle of passive defense based on environmental capabilities is unarmed action that caused the reduction of human resources vulnerability، buildings، equipment، documents and arteries of the country against the crisis by natural factors such as drought، flood، earthquake، etc. Considering the possible occurrence of such risks in population centers، ready to deal with what is known unpleasant and undesirable consequences is necessary. On this basis and given the importance of population centers in Helle and Mond basins، in this study، the authors tried to analyze the Rain hazards of drought and flood. The study area،Helle and Mond basins، with about 21،274، 47653 km2 area، respectively are located in the south of Iran. The Helle basin approximately is between 28° 20'N and 30° 10'N latitudes and between 50° E and 52° 20'E longitudes and Mond basin is between 27° 20' and 29° 55' latitudes and between 51° 15' and 30° 27'E longitudes.These basins are located in sides of a massive sources of moisture، Persian Gulf. In this study، data from 23meteorological and synoptic stationsstations، during aperiod of20 years (1992-2011)in northern region of the Persian Gulf (Mond and helle basins)were used to calculate Standardized Precipitation Index (SPI). The data were collected by the Iranian Meteorological data website (http://www.weather.ir). The SPI is primarily a tool for defining and monitoring drought events. This index may be computed with different time steps (e.g. 1 month، 3months، 24 months). The SPI is defined for each of the above time scales as the difference between monthly precipitation (xi) and the mean value ( )، divided by the standard deviation. To assess flood risk zones، the flood، annual evapotranspiration، cities and populations centers layers were collected in Helle and Mond basins position. The annual precipitations and the SPI maps were drawn by Geostatistics، Kriging. It also the flood and annual evapotranspiration layers were weighted by Euclidian distance method، separately. Finally، all layers are weighted by AHP and fuzzy-linear methods (descending and ascending linear function) into vulnerable layers. The final map of vulnerable areas with flood and drought high risk was drawn based on the algorithm of linear-Fuzzy in a raster format. According to the results، eastern، north eastern and south eastern part of Mond basin had high annual precipitation. Based on this result، it said that these parts of study area were known the least dangerous areas of vulnerability. The results also showed that with passing of the western regions and going to the center of the study area the annual rainfall have been added over the years. Kazeron، Chenar Shahijan، Firouz Abad، Borm plains and some parts of Khane Zenyan and Dash Arzhan are cities located in this regions. Low latitude، Proximity to the warm waters of the Persian Gulf، low annual precipitation and high temperature causing evaporation and inappropriate environmental conditions in Boushehr province and some coastal cities such as Genaveh، Deilam، Boushehr، Baghan، Lar and Khonj. Accordingly، west، north west، south and south west regions in Helle basin were located in extreme vulnerability zone with a loss of annual rainfall for drinking and agricultural production and poor nutrition underground aquifers.