Urbanization and Floods in Sub-Saharan Africa: Spatiotemporal Study and Analysis of Vulnerability Factors—Case of Antananarivo Agglomeration (Madagascar)

Learning from history of natural disasters in the Sahel: a comprehensive analysis and lessons for future resilience

One of the first environmental crises to attract interest in development initiatives and aid was the great drought of the 1970s in the Sahel. This study investigates the extent of damage caused by natural disasters from one of the most widely used databases-EM-DAT-with a sample size of 16 Sahelian countries over the period 1960-2020. These countries have been divided into three regions: Western Africa Sahel (WAS), Central Africa Sahel (CAS), and Eastern Africa Sahel (EAS). The analyses encompass four categories of natural hazards, namely, biological, climatological, hydrological, and meteorological. We used descriptive and test statistics to summarize the natural disaster records. Through this approach, we explore tendencies to identify the most frequently reported natural hazards; we examine their spatial distribution and evaluate their impacts in terms of socioeconomic damage and causalities. During the study period, a total of 1000 events were recorded in the database. The Western Africa Sahel (WAS) region had the highest number of disasters, with 476 events, followed by the Eastern Africa Sahel (EAS) region with 369 events. The most common hazards in the Sahel were hydrological (41.8%), mainly floods, and biological (39.5%) hazards. Approximately 300 million people in the Sahel were affected by natural hazards, with 59.17% in EAS, 36.48% in WAS, and 4.35% in CAS. Although droughts occurred less frequently (14%), they had a significant impact on the population, affecting 84% of those affected by natural hazards. In general, EAS experiences a higher impact from natural hazards, potentially influenced by the pastoral lifestyle of its population. However, WAS is also very vulnerable to natural hazards especially epidemics and nowadays floods. The uncontrolled urbanization in the area may contribute to this vulnerability.

Flood susceptibility assessment of the Agartala Urban Watershed, India, using Machine Learning Algorithm

Frequent floods are a severe threat to the well-being of people the world over. This is particularly severe in developing countries like India where tropical monsoon climate prevails. Recently, flood hazard susceptibility mapping has become a popular tool to mitigate the effects of this threat. Therefore, the present study utilized four distinctive Machine Learning algorithms i.e., K-Nearest Neighbor, Decision Tree, Naive Bayes, and Random Forest to estimate flood susceptibility zones in the Agartala Urban Watershed of Tripura, India. The latter experiences debilitating floods during the monsoon season. A multicollinearity test was conducted to examine the collinearity of the chosen flood conditioning factors, and it was seen that none of the factors were compromised by multicollinearity. Results showed that around three-fourths of the AUW area was classified as moderate to very high flood-prone zones, while over 20 percent was between low and very low flood-prone zones. The models applied performed well with ROC-AUC scores greater than 70 percent and MAE, MSE, and RMSE scores less than 30 percent. DT and RF algorithms were suggested for places with similar physical characteristics based on their outstanding performance and the training datasets. The study provides valuable insights to policymakers, administrative authorities, and local stakeholders to cope with floods and enhance flood prevention measures as a climate change adaptation strategy in the AUW.

Flood vulnerability assessment of Thailand's flood-prone Pathum Thani province and vulnerability mitigation strategies

This research assesses the flood vulnerability of Thailand's flood-prone province of Pathum Thani using a comprehensive vulnerability assessment framework. The assessment framework incorporates three key components: exposure, sensitivity, and adaptive capacity, consisting of 10, 12 and 11 flood vulnerability indicators, respectively. The flood vulnerability components and the flood vulnerability indicators are statistically validated by confirmatory factor analysis to determine the factor loadings and reliability of the components and indicators. The flood vulnerability questionnaire corresponding to the flood vulnerability indicators is subsequently developed and applied to the flood-prone districts of the province. The results show that proximity to rivers (with an indicator score of 0.685), household debt levels (0.612), land use patterns (0.617), and the proportion of low-income households (0.621) significantly contribute to the flood exposure of the province (with an exposure index score of 0.531). Larger household size (with an indicator score of 0.901), disruptions in public utility services (0.747), and workplace absenteeism due to flooding (0.741) contribute to the province's higher flood sensitivity (with a sensitivity index score of 0.633). Drainage capacity of natural and man-made waterways (0.571) contributes to low to moderate levels of flood adaptive capacity. The flood vulnerability of seven administrative districts of Pathum Thani, as measured by the flood vulnerability index scores (0.454-0.608), range from moderate to high. Local authorities need to invest in flood warning and response systems, prioritize infrastructure development and encourage community engagement to reduce the flood vulnerability.

Characterizing the level of urban Flood vulnerability using the social-ecological-technological systems framework, the case of Adama city, Ethiopia

This study characterizes the flood vulnerability of Adama City, Ethiopia, where the city faces high flood vulnerability due to its unplanned urbanization in low-lying floodplain areas surrounding deforested mountains and ridges. The study applied an interlinked Social-Ecological-Technological-Systems (SETS) vulnerability framework using a GIS-based Multi-Criteria Decision-Making and Analytical Hierarchy Process (MCDM-AHP). The framework analyzed exposure, sensitivity, and adaptive capacity to flooding for each of the three SETS domains. The study analyzed 18 variables at the city level within each SETS domain. The result revealed that clusters of flood-vulnerable areas were identified by each SETS domain showing the concentration of flood vulnerability in the study area and the need to consider prompt adaptive mechanisms to severe and recurring flooding. The finding has significant implications for holistic approaches to sustainable cities. Moreover, the reduction of complex urban flood vulnerabilities according to their priority as individual or combined solutions for decision-makers and professionals in early warning and flood management systems is the other contribution of the study.

Health effects of climate change in Africa: A call for an improved implementation of prevention measures

The world's climate, particularly in Africa, has changed substantially during the past few decades, contributed by several human activities. Africa is one of the continents that is most vulnerable to climate change globally. Since the beginning of 2022, extreme weather events in Africa have affected about 19 million people and killed at least 4,000 individuals. Cyclones, floods, heatwaves, wildfires, droughts, and famine were among the severe weather occurrences. Natural disasters and extreme weather events brought on by climate change may compromise access to clean water, sanitation systems, and healthcare facilities, making people more vulnerable to a number of illnesses. Floods and drought can lead to both communicable and non-communicable diseases. The African population is more likely to experience more mental health disorders than before because of natural disasters, which result in the loss of property and sometimes loss of lives more frequently. We, therefore, call for an improved implementation of strategies to prevent the health effects of climate change so that the health of the people in Africa can be maintained.

Flood hazards and risk mapping using geospatial technologies in Jimma City, southwestern Ethiopia

Cities in Ethiopia are suffering from unprecedented floods due to climate change and other anthropogenic activities. Failure to include land use planning and poorly designed urban drainage system aggravates the problem of urban flood. The integration of geographic information system, and multi-criteria evaluation (MCE) technique were used for flood hazards and risk mapping. Five factors namely slope, elevation, drainage density, land use land cover, and soil data were used for flood hazards and risk mapping. Agrowing urban population increases the risk of flood victims during the rainy season. Results revealed that about 25.16 and 24.38% of the study area is categorized under very high and high flood hazards, respectively. The topographic nature of the study area increases flood risk and hazards. The increaseing number of people living in the city has led to the conversion of previously occupied green lands into residential areas aggravates flood hazards and risk. Flood mitigation measures such as better land use planning, public awareness creation on flood hazards and risks, delineation of flood risk areas during the rainy seasons, increasing greenery, strengthening river side development, and watershed management in the catchment are urgently required. The findings of this study can provide a theoretical background for flood hazards risk mitigation and prevention.

Flood Hazard Zoning of Upper Awash River Basin, Ethiopia, Using the Analytical Hierarchy Process (AHP) as Compared to Sensitivity Analysis

Floods and droughts have been two of the most devastating consequences of the climate crisis affecting billions of people in the world. However, unlike the other natural hazards, flooding is manageable through appropriate flood management mechanisms. This study emphasizes on developing a flood hazard zone for the Upper Awash River Basin (UARB), Ethiopia. Six relevant climate, physiographic, and biophysical factors were considered. Then, a flood hazard map was developed employing the analytic hierarchy process (AHP) method and further validated using sensitivity analysis and collected flood marks. The results revealed that drainage density, rainfall, and elevation have higher significance, while land use and soil permeability have a low impact in the process of flood generation. The map showed vulnerable areas at different levels and can serve as a valuable input for the decision makers to consider in the process of implementing emergency plans as well as long-term flood mitigation options.

Flood hazard management in a multiple hazard context: a systematic review of flood hazard management during the COVID-19 pandemic in Africa

Result-oriented research can uncover hidden flood management obstacles and propose solutions that, if combined with political will, appropriate technology, and resources, can overcome the majority of Africa's future flood calamities. In view of this, it is critical to examine researchers' findings on flood hazard management, particularly now that the continent is struggling with COVID-19 and other hazards. This study employed a systematic review approach to critically analyze 103 contextually detailed studies with a set of criteria that were not only meant to keep the focus on floods and the COVID-19 pandemic but also to understand the context of managing floods during COVID-19 and other hazards at the same time on the continent. I found that the authors strongly recommend how institutions should create non-structural enabling environments for managing combined hazards. Also, researchers paid little attention to recommending ecosystem-based measures for flood management during the COVID-19 pandemic in Africa. Future research should study how different countries in Africa are preparing to manage multiple future hazards, including the comparative assessment of the strengths and weaknesses of individual countries' planning and preparation.