Spatial Analysis of Vulnerability of Urban Land uses Against Floods (Case study: Raaz City, Northern Khorasan province)

Floods are considered one of the most important hazards causing a lot of damage to urban areas. Due to its increasing frequency in recent years, urban flooding is one of the most threatening natural hazards in urban areas around the world. To prevent floods and reduce the consequences, city managers should warn the residents of high-risk areas by predicting the features of rainfall such as peak intensity, arrival time, and duration, along with taking emergency measures while predicting floods. Since urban flood risk mapping has a decisive role in urban management and planning, especially in reducing flood damage, it is necessary for city planners and urban planners, geologists, and geographers to examine the causes and factors related to these events for the purpose of dealing with such natural disasters in urban areas and predicting the necessary solutions to reduce their effects. The present study aims to analyze vulnerable urban areas spatially against floods in the city under study and provide solutions to reduce vulnerability while determining the areas at risk.

In this descriptive and analytical study, library studies and questionnaires were used for collecting the related information. The statistical population included experts related to urban planning and natural resources, water and sewage, environment, as well as other official institutions related to Raaz city. To avoid bias, the experts’ opinions were considered for determining and weighing the criteria. Finally, 40 people were selected based on a purposive sampling method. GIS software and AHP hierarchical analysis were used for data analysis. After determining the weights and calculating the reliability rate of the indicators and their confirmation coefficient, vulnerable areas were prioritized by using GIS software and the output was a map recognized in three layers including the high priority (high vulnerability), low priority (medium vulnerability) and non-priority (vulnerability) low) areas.

To evaluate the vulnerable areas caused by floods in Raaz city, the variables used in this study were classified into two groups. First, the aggravating elements are the elements that increase the vulnerability of land uses against floods including the slope of the land and waterway network. Second, there are elements at risk, which are divided into basic, vital, and spatial elements. Basic elements are those which are directly exposed to flood risk. Because flooding bridges during heavy rains is one of the most common problems of urban runoff, urban bridges are one of the basic elements at risk of flooding. In this research, the effective variables in vulnerability such as land use, distance from the bridge, population density, slope, and density of the waterway network were considered for determining the overall weight, their prioritization based on the relationships in the 5x5 matrix to compare the variables two by two and determine the preference. The findings indicated that residential and cultural uses were built at zero distance from the river in Raaz city without observing the privacy of the river. In addition, educational, industrial, agricultural, and religious uses were built at a distance of 13 and 15 meters from the river. The use of the AHP hierarchical analysis model and GIS software of the extent and areas vulnerable to floods in Raaz city showed that residential, cultural, religious, and medical uses have the highest percentage of vulnerability to urban floods.

 Based on the results, 33% of the area in Raaz city is exposed to high vulnerability due to floods, most of which are related to residential use due to the small size of the city and the lack of other uses. This vulnerability is mostly related to the slope of the land, the low quality of the buildings, and the lack of observing the privacy of the river as the most important reason for the vulnerability of residential use.