واکاوی میزان اثرگذاری عوامل موثر بر سیل خیزی استان همدان با استفاده از مدل آنتروپی شانون و سیستم اطلاعات جغرافیایی

سیل به‌عنوان یک مخاطره طبیعی از عوامل مختلف طبیعی و انسانی ناشی می‌گردد. بدون شک میزان تاثیرگذاری این عوامل بر بروز سیل یکسان نیست و شناسایی میزان اثرگذاری و وزن هر یک از پارامترهای تاثیرگذار بر سیل از ضروریات است. این تحقیق میزان اثرگذاری عوامل طبیعی ایجاد سیلاب ازجمله اقلیم (شدت، مدت و احتمال وقوع بارش و مانند آن) و دیگر پارامترهای هیدرولوژیکی موثر بر آن را شناسایی کرده و به تشخیص مناطق پرخطر و سیل‌خیز در سطح استان همدان پرداخته است. مدل انتخابی برای این تحقیق مدل آنتروپی شانون (روش ترکیبی داده‌ای – کارشناسی) است که بر اساس داده‌های اقلیمی، هیدرولوژی و توپوگرافی توام با نظریات کارشناسی اقدام به وزن‌دهی به عوامل طبیعی موثر در بروز سیلاب شده است. بر این اساس بیشترین وزن را حداکثر 24 ساعته بارش داشته است. نتایج نشان می‌دهد این پارامتر موثرترین عامل طبیعی ایجادکننده سیل در استان همدان است. عوامل پوشش گیاهی، زمان ذوب برف، شیب حوزه، جنس زمین وضریب گراولیوس به ترتیب بیشترین اوزان را به خود اختصاص داده‌اند. بر اساس اوزان نهایی نقشه خطر با استفاده از سیستم اطلاعات جغرافیایی ترسیم شد که نشان می‌دهد مناطق با خطرپذیری بسیار زیاد در مناطق مرکزی و جنوبی استان واقع‌شده است. بیشتر شهرستان‌های استان در مناطق با خطرپذیری زیاد قرار گرفته‌اند. بر این اساس در شهرستان‌ها مناطق آسیب‌پذیر بیشتر در حریم سیلابی رودخانه‌ها واقع‌شده است.

Analysis of the effect of factors affecting flooding in Hamadan province using Shannon entropy model and GIS

1 Introduction Natural hazards cause enormous damages every year. Among the natural hazards, floods, earthquakes, and droughts have special importance in financial and human losses. Meanwhile, according to the available statistics and information, floods in some parts of the world, especially in Asia and Oceania, have the highest damage. Iran is one of the arid and semiarid regions of the world with particular climatic conditions. Inappropriate spatiotemporal distribution of rainfall in such regions has caused devastating floods. In this study, flood vulnerable areas are identified by determining the effective parameters of flood using Shannon entropy model. The results of this study can be used in flood zoning and forecasting and planning and management of water resources in the region. 2 Materials & Methods In multicriteria decisionmaking problems having and knowing the relative weights of the existing indicators is a significant step in the problemsolving process. (Relations 1 to 6).     (1)   Aij= (2)   (3)   (4) Ej=  i=1,2…,m                                       (5) wj=dj/∑dj (6) wj= Entropy method is one of the multicriteria decisionmaking methods for calculating the weight of criteria. This method requires a criterionoption matrix. The steps of Shannon entropy method consist of five steps of the decision matrix, normalization of the decision matrix, calculation of the entropy of each index, the calculation of deviation, and calculation of weight value Wj.     In the Shannon method using the experience and knowledge of experts appropriate factors are determined and weighed. After collecting the questionnaire data and considering the geography of the study area, the scores of each factor are adjusted. 3 Results & Discussion Natural parameters of flood occurrence in Hamadan province include: climate, snowmelt, slope, soil type, Gravilius coefficient, and vegetation. Due to the climatic characteristics of the province, most of the province’s rainfall is due to the Mediterranean systems. In winter, the rains are in the form of snow, and in the early spring the melting of snows is accompanied by spring rains which most of the time causes the rivers to overflow. Due to the severe destruction of vegetation in the province, the potential of the region in flooding has been increased. In general, it can be said that the occurrence of floods in any region is due to the confrontation and alignment of human and natural factors. This study only examines the natural causes of flood. The study of the effect of each parameter in the occurrence of floods based on the dataexpert method showed that the six factors studied in these studies do not have the same effect on reducing or increasing floods in the basins. 4 Conclusion Based on scoring the natural factors that cause floods, according to the intensity of their impact, the floodprone areas of the province have been identified. Based on the combined data model and Shannon entropy, the highest weighting was given to the maximum 24hour precipitation. Vegetation factors, snow melting time, basin slope, soil type and Gravilius coefficient were identified as the most effective natural factors in causing floods in Hamadan province, respectively. Based on the final weights, a hazard map was drawn using the GIS. According to the hazard map, the very high risk regions are located in the central and southern parts of the province. Also, the northern areas including the cities of Razan, Kaboudar Ahang and Dargazin are located in high risk area.   Using the results of this study, it is possible to identify the approximate time of flood occurrence and floodprone areas in Hamedan province.