Flood Hazard and Flood Risk Vulnerability Mapping Using Geo-Spatial and MCDA around Adigrat, Tigray Region, Northern Ethiopia

Abstract

In Ethiopia, urban floods incidents are becoming a serious problem in recent years. They are mainly associated with poorly designed urban drainage system and land use planning. Combined to it, lack of early warning system and organized flood disaster mitigation measures at national and local level further increases the gravity of the problem. Adigrat is one of the north Ethiopian towns which is frequently attacked by these floods. To understand and address the issue, a study was conducted around Adigrat town with the aim to spatially delineate the flood hazard and risk with the help of geo-spatial and multi-criteria decision analysis (MCDA) tools. Baseline maps were developed using Landsat satellite images, DEM, aerial photographs, rainfall data and census population data. Different variables like slope, elevation, rainfall, water table, flow direction and flow accumulation, LULC, population density, building density and road density were considered for developing a model. After the data is collected and organized, Erdas Imagine and ArcGIS software were used to process and prepare the model, and finally weighted overlay model was adopted to stimulate the prototype. Each baseline maps was weighted against its impact since all factors have no the same importance. Accordingly, slope, LULC, elevations; and population density, flood hazard and LULC were found the most important factors. The flood risk areas are delineated based on flood hazard, LULC, population density, road and building density. The results indicate that the Kebeles03, 04 and 05 (center of the town) with flat slopes, low altitudes, more population and significant amount of built up area are found to be the most vulnerable for flood hazard. On the other hand, the Kebeles 01, 02 and 06 lying southwest and west of the study area are least affected by flood due to steep topography and high altitudes. It is suggested that similar type of inter-disciplinary studies are essential to minimize the damages and assure sustainable urban development.

Natural and Socioeconomic Factors and Their Interactive Effects on House Collapse Caused by Typhoon Mangkhut

“…Slope (SP) was another significant factor associated with the house collapse rate, with a determinant power of 0.17, and exerted a notable effect on the house collapse rate that was comparable to the results of some previous studies (Smyth and Royle 2000;Fernandez and Lutz 2010). Nigusse and Adhanom (2019) reported that, in areas with flat slopes and lower elevations, more people and buildings are the most vulnerable to flooding. Smyth and Royle (2000) demonstrated that slope has an important effect on house damage.…”

“…Based on a comprehensive consideration of the hazard, the environment, the vulnerability of the affected communities, the disaster prevention and reduction capacity (Shi et al 2020), the results of previous studies (Gong and Hu 2015;Hu et al 2018;Nigusse and Adhanom 2019;Yuan et al 2020), and the availability of data, the 2018 house structures for each county of the study area that is the ratio of steel-concrete houses (RS), the ratio of brick-concrete houses (RC), and the ratio of brick-wood houses (RB) were taken as the explanatory variables. The variables of the socioeconomic factors for each county included the population density (PD), per capita GDP (PG), the ratio of urban to rural population (UR), high school penetration rate (HS), per capita housing area (PA), and the proportion of the tertiary industry (PT).…”

“…Huang and Cheng (2013) reported that, when hit by a typhoon, the collapse of a house is affected by the local elevation. Nigusse and Adhanom (2019) demonstrated that elevation is one of the most important parameters when typhoons hit. Yuan et al (2020) also demonstrated that elevation was the most influential factor when a typhoon arrives.…”

“…With the rapid growth of urbanization, socioeconomic activities will affect these causes. Since the 1980s, research on typhoon disasters has increasingly focused on safety improvement with respect to the economy and society, and has attached great importance to the vulnerability of human economic, social, and cultural systems to natural hazard-induced disasters (Vrijling et al 1995;Nigusse and Adhanom 2019). This has since become a multiscale, comprehensive concept influenced by nature, society, the economy, and the environment (Cheung 2007).…”

“…This has since become a multiscale, comprehensive concept influenced by nature, society, the economy, and the environment (Cheung 2007). In recent years, the association between disaster losses caused by typhoons and the socioeconomic conditions has attracted great attention from researchers in multidisciplinary fields, such as economics, urbanization, construction, and demographics (Vrijling et al 1995;Nigusse and Adhanom 2019).…”