Land Use and Land Cover Change Assessment in the Context of Flood Hazard in Lagos State, Nigeria

Dorcas Idowu,Wendy Zhou

doi:10.3390/w13081105

Abstract

Incessant flooding is a major hazard in Lagos State, Nigeria, occurring concurrently with increased urbanization and urban expansion rate. Consequently, there is a need for an assessment of Land Use and Land Cover (LULC) changes over time in the context of flood hazard mapping to evaluate the possible causes of flood increment in the State. Four major land cover types (water, wetland, vegetation, and developed) were mapped and analyzed over 35 years in the study area. We introduced a map-matrix-based, post-classification LULC change detection method to estimate multi-year land cover changes between 1986 and 2000, 2000 and 2016, 2016 and 2020, and 1986 and 2020. Seven criteria were identified as potential causative factors responsible for the increasing flood hazards in the study area. Their weights were estimated using a combined (hybrid) Analytical Hierarchy Process (AHP) and Shannon Entropy weighting method. The resulting flood hazard categories were very high, high, moderate, low, and very low hazard levels. Analysis of the LULC change in the context of flood hazard suggests that most changes in LULC result in the conversion of wetland areas into developed areas and unplanned development in very high to moderate flood hazard zones. There was a 69% decrease in wetland and 94% increase in the developed area during the 35 years. While wetland was a primary land cover type in 1986, it became the least land cover type in 2020. These LULC changes could be responsible for the rise in flooding in the State.

Highlights

Located in Nigeria’s southwestern zone, Lagos State is regarded as a hotspot in terms of urban expansion
This section describes the results from landcover classifications for the images acquired in 1986, 2000, 2016, and 2020, as well as the Land Use and Land Cover (LULC) change detection in the context of flood mapping
Our study revealed that of all the land cover types identified in Lagos State, decrement in wetland and increment in developed areas consist of the most land cover changes from 1986 to 2020

Summary

Introduction

Located in Nigeria’s southwestern zone, Lagos State is regarded as a hotspot in terms of urban expansion. The city currently ranks number seven in the fastest growing cities and urban areas globally, with an average annual growth of 4.4% in population from 2006 to 2020. It continues to grow in population density and urbanization, with a current population of over 21 million and over 6000 residents per square kilometer. Urban sprawl means the loss of wetland, forest, and agricultural land to houses, roads, and industries, leading to environmental challenges and changing demographics [4]. Environmental challenges, such as flooding, are the major natural disaster that plagues Lagos State, which is assumed to be stimulated by urban sprawl. Monitoring urban sprawl and identifying the pace of the spread and spatial pattern is a primary concern for urban

Objectives

Results

Discussion

Conclusion