Flood Inundation Mapping Using Remote Sensing and GIS Techniques: A Case Study of Sokoto plain, Nigeria

Author: Oluwadamilare Olawale Ajayi

Ajayi, Oluwadamilare Olawale, 2016 Flood Inundation Mapping Using Remote Sensing and GIS Techniques: A Case Study of Sokoto plain, Nigeria, Flinders University, School of the Environment

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Flooding is one of the most frequent and devastating natural disasters and can often result in severe damage to agricultural products, commercial infrastructure, personal property and loss of human lives. Accurate delineation of flooded waters is an important research issue in determining both economic and personal risk. Determining the spatial extent and temporal pattern of flood inundation events has largely been achieved using remotely sensed imagery due to its synoptic and repeatable abilities. Along with Geographical Information Science (GIS) techniques, these technologies help facilitate the development of rapidly accessible inundation and vulnerability maps that will help prioritize mitigation efforts. This is particularly important in developing countries such as Nigeria where population growth is rapid and flood management resources are scarce. Specifically, this study focuses on the Sokoto-Rima river system in Sokoto State, Nigeria. The river system is key to the local agrarian economy and is subject to frequent flood events that have impacted upon agrarian systems and displaced thousands of people in recent years.

Central to this study is the use of the Moderate Resolution Imaging Spectroradiometer (MODIS), which offers frequent synoptic coverage at a national scale and is freely available. Multitemporal MODIS imagery is used here to measure flood frequency and extent through the Modified Normalised Difference Water Index (MNDWI) for selected flood periods 2003, 2010, 2012 and 2015. LandScan GRID population data from Oaks Ridge National Laboratory (ORNL) and the projected population data derived from the most recent Nigerian census data 2006 is used to estimate population vulnerable to flood inundation.

The delineation of inundated areas from non-inundated areas was undertaken using a threshold technique of the Modified normalized difference water index (MNDWI). The frequency and maximum spatial extent of floods, generated by comparing the four periods of flood extents, was informative and identified populations and Local government areas (LGAs) vulnerable to flooding. In a developing country where spatial information and infrastructure is limited, we report a simple, cost effective, and successful approach to detecting and mapping floods in the Sokoto region. Considering that MODIS data products are freely available and have broad national coverage that allow frequent observations, the results demonstrate a cost effective method of detecting and quantifying the extent of floods in Sokoto, Nigeria.

Keywords: RS, GIS, Flood, MODIS, NDVI, NDWI, MNDWI, LandScan, Sokoto

Subject: Environmental Science thesis

Thesis type: Masters
Completed: 2016
School: School of the Environment
Supervisor: Stephen Fildes