Tarihi kentsel çevreler için varolan sistemde koruma çalışmaları ve afet riski azaltımı, birbirinden bağımsız işleyen iki süreçtir. Bu makalede, tarihi kentsel çevrenin bütünü ve kentsel kültür mirası için doğal afet kaynaklı risklere yönelik bir analiz yöntemi önerilmektedir. Bu risk analiz yöntemi, Adalar-Büyükada yerleşimi genelinde deprem, yangın ve sel afetleri için denenmiştir. Önerilen risk analiz yöntemi, Analitik Hiyerarşi Süreci (AHS) ile Büyükada için ağırlıkları tanımlanan ve kentsel kültür mirası alanlarında en çok hasar veren doğal afetlerden deprem, yangın ve sel risklerini içermektedir. Bu kapsamda analizler şu bileşenlerden oluşmaktadır: Deprem riski analizi; zemin tehlike analizi, tsunami tehlike analizi ve yapısal hasargörebilirlik analizini: Yangın riski analizi; yangın çıkış riski analizi ve yangın yayılma riski analizini; Sel/su baskını riski analizi; aşırı yağış nedeniyle oluşan su baskını riskinin analizi ve su toplama yapılarının hasar görmesi sonucu oluşan su baskını analizini içermektedir. Büyükada örneğinde baraj gibi su toplama yapıları bulunmadığından yalnızca su dağıtım hatları ve aşırı yağışa bağlı olarak eğim ve zemin özellikleri nedeniyle gerçekleşebilecek su baskını için riski analizi yapılmıştır. Analiz kapsamında belirlenen risk faktörleri ve bunların AHS ile oluşturulan ağırlıklarına bağlı olarak her bir risk için ayrı ve toplam riske yönelik CBS ortamında risk haritaları hazırlanmıştır. Büyükada'da doğal afetlerden kaynaklanan risklerin analizi sonucunda toplam tescilli yapı parsellerinin alansal olarak % 40.2'sinin, çok yüksek fiziksel çevre kaynaklı risk altında olduğu görülmüştür. Anahtar Kelimeler: Kentsel kültür mirası, doğal afetler, risk analizi, CBS, AHS, İstanbul-Büyükada. Existing issues in the research area of risk mitigation for urban cultural heritage in Turkey are mainly attributable to absence of a common and defined risk management system among the stake-holders that are responsible from risk mitigation at historical urban environments. Within this context this paper aims, to define a risk analysis system based on Analytic Hierarchy Process and spatial analysis methods within Geographic Information Systems-GIS that would guide for analysis of natural disaster related risks that threaten urban cultural heritage. Suggested methodology is implemented within Büyükada context. The sources of risks that threaten urban cultural heritage can be categorized such as physical, social, economic, political and technical /organizational however; it should also be noted that there are risks that can be a combined result of different categories of risk and not to mention that risk in itself is a multi layered concept. For instance a privately owned cultural heritage building might long be neglected due to different preferences of the owner and when it is demolished by an earthquake, the causative reason for this, is rooted in both the socio-cultural and the physical environment related risk factors. In Turkey, urban cultural heritage is under risk at many different levels. Aside from high earthquake risk, flooding and fire, other risk factors generated by political, social or economic factors include recent examples of Hasankeyf, an archeological heritage site that will be flooded by the completion of the Ilisu Dam; a conservation attitude that has been demoted to just keep the facades of heritage buildings in Tarlabaşı. Risk analysis for urban cultural heritage includes following steps: Analysis of existing structures and natural environment; Defining main risk sources and related risk factors for the heritage area; Prioritizing the causative risk factors and evaluating their weightings and rank; Evaluating each risk source independently and overall evaluation. Risks that are caused by natural disasters such as earthquake, flood and fire are among the costliest and most hazardous risks for heritage areas. Therefore risk analysis focuses on these natural disasters. Earthquake, fire and flood have been chosen among the risks that are caused by factors related to the physical environment. Within earthquake risk analysis: “Ground hazard analysis” where geological structure and their possible earthquake behavior is analyzed; “Tsunami hazard analysis” is made as an integrated analysis of possible earthquake affect through the sea topography, bathymetry and “Structural vulnerability analysis” is conducted where building behavior is assessed regarding to building type and condition. Fire risk analysis is combined of fire ignition and fire spread risk analysis. Fire ignition risk analysis includes analysis of explosive or flammable usage and areas. Fire spread risk analysis factors that affect the spread of the fire such as vegetation type and density, wind and slope. Within flood risk analysis, ground hazard analysis and vulnerability analysis of water distribution structures are made. Ground hazard analysis includes the geological formation that affects the permeability of the ground and topography of the area. Vulnerability analysis of water distribution structures includes the damage and the possible affected area that is around these structures. For Büyükada since there is no water collecting structures such as dams. Only ground water capacity analysis has been made. Risk factors are examined and their weightings have been defined for each risk with AHP in order to form raster image with spatial analysis within GIS for each risk sector. Risk analysis for Büyükada shows that %40,2 of all urban cultural assets are under very high risk of natural disasters. Fire and earthquake is more likely to cause damage on the overall Büyükada and urban cultural heritage. Earthquake risk is high due to ground properties, location of fault line and condition of existing building stock. Fire risk is rooted from high proportion of wooden structures, located close to dense forest area and fire ignition spots such as electricity distribution stations and LPG storage units. Adalar fire brigade is located on a high tsunami risk area, which might cause a secondary risk for uncontrolled fire at an event of earthquake and tsunami. Büyükada risk analysis reveals the most problematic areas, which would be beneficial in prioritizing resources within risk mitigation processes. Büyükada is isolated and carrying disadvantages of being an island, therefore the system and the infrastructure should be self-sufficient. Keywords: Urban cultural heritage, natural disasters, risk analysis, GIS, AHP, Istanbul-Büyükada
