GIS-Based Climate Change Induced Flood Risk Mapping in Uhunmwonde Local Government Area, Edo State, Nigeria
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International Journal of Environment and Climate Change 10(9): 8-23, 2020; Article no.IJECC.58768 ISSN: 2581-8627 (Past name: British Journal of Environment & Climate Change, Past ISSN: 2231–4784) GIS-Based Climate Change Induced Flood Risk Mapping in Uhunmwonde Local Government Area, Edo State, Nigeria Obot Akpan Ibanga1* and Osaretin Friday Idehen2 1Department of Geography and Regional Planning, University of Benin, Benin City, Edo State, Nigeria. 2Department of Geography and Regional Planning, Igbinedion University, Okada, Edo State, Nigeria. Authors’ contributions This work was carried out in collaboration between both authors. Author OAI designed the study, performed the statistical analysis, wrote the protocol and wrote the first draft of the manuscript. Author OFI managed the literature searches and analyses of the study. Both authors read and approved the final manuscript. Article Information DOI: 10.9734/IJECC/2020/v10i930225 Editor(s): (1) Dr. Arjun B. Chhetri, Dalhousie University, Canada. Reviewers: (1) Valeriya Ovcharuk, Odessa State Environmental University, Ukraine. (2) Jagannath Jadhav, Visvesvaraya Technological University, India. Complete Peer review History: http://www.sdiarticle4.com/review-history/58768 Received 07 May 2020 Accepted 11 July 2020 Original Research Article Published 25 July 2020 ABSTRACT Introduction: Flood is one of the climate change induced hazards occurring in most parts of the world. It exposes humanity and many socio-ecological systems to various levels of risks. In Nigeria, extreme rainfall events and poor drainage system have caused inundation of several settlements to flooding. To contain the disaster, risk mapping were among the measures recommended. Aims: The aim of this paper is to highlight flood risk zones (FRZ) in Uhunmwonde Local Government Area (LGA), Edo State, Nigeria. Methodology: Flood risk (FR) was mapped using hazards and vulnerability and implemented using geographic information system (GIS)-based multi-criteria analysis analytic hierarchy process (MCA-AHP) framework by incorporating seven environmental and two socio-economic factors. Elevation, flow accumulation, soil water index of wettest quarter, normalized difference vegetation index, rainfall of wettest quarter, runoff of wettest quarter and distance from rivers constituted the hazard component while population density and area of agricultural land use was the vulnerability _____________________________________________________________________________________________________ *Corresponding author: E-mail: [email protected]; Ibanga and Idehen; IJECC, 10(9): 8-23, 2020; Article no.IJECC.58768 layer. The climate change induced flood risk was validated using the responses of 150 residents in high, moderate and low flood risk zones. Results: The resulting flood risk map indicated that about 40.4% of Uhunmwonde LGA fell within high flood risk zone, 35.3% was categorized under moderate flood risk zone whereas low flood risk zone extended up to about 24.3% of the LGA. The high number of respondents who reported occurrence of flooding with frequency being very often and the fact that flooding was a very serious environmental threat during on-the-spot field assessment validated the generated climate change induced flood risk. Conclusion: The utilitarian capabilities of GIS-based MCA-AHP framework in integrating remotely- sensed biophysical and climate change related flood inducing indicators with socio-economic vulnerabilities to arrive at composite flood risk was demonstrated. Keywords: Flood hazard; vulnerability; flood risk; GIS; mapping; uhunmwonde LGA. 1. INTRODUCTION 2017, over three billion dollars’ worth of properties and cultivated farmland in several Flooding has been acknowledged as one of the places in USA were lost to climate change direct consequences of climate change [1] due to induced flooding. This was as result of increase increase in the frequency and intensity of tropical in the frequency and intensity of rainfall coupled cyclones, hurricanes, typhoons and other with increased development in floodplains, moisture-laden extreme weather phenomena [2]. increased impermeable surfaces (roads, The warmer than normal global temperature [3] pavements, and parking lots), destruction of is an invitation for increase in convective natural areas [13]. In the United Kingdom (UK), activities in the earth’s atmosphere [4] with two days continuous rainfall in October 2019 resultant increase in the amount and duration of similar to the already reported monthly value as a rainfall [5]. Melting of ice caps in the Polar result of successive stormy activities made Regions directly linked to global warming and several locations to be inundated to flood waters worldwide changes in the level of water in the [5]. Nigeria occupied the 10th position in terms of oceans leading to upsurge in coastal and river food occurrence and vulnerability annually [12]. flooding have also been documented [3,6,7]. The current worldwide mean annual increase of 3- In climate change debates, flood risk has been 4mm in water levels in the oceans and the conceptualized as the product of three principal predicted rise to about 15 mm at the end of the components namely: hazard or exposure, present century is also responsible for the sensitivity or elements at risk and vulnerability frequency and magnitude of flooding [8]. [6,7,14]. Risk practitioners view risk as the product of the probability of an event’s However, a shift in climate has been ascribed to occurrence and its magnitude (i.e., probability × the actions of man which modifies atmospheric magnitude = risk). However, in environment and processes as well as the noticeable natural development debates, this relationship include spatial and temporal fluctuations in global an exponent to account for social values or climatic pattern [3,9]. In contrast, flood or flooding societal impacts (i.e., probability × magnitude n), is the accumulation of excessive quantity of although n may be difficult to measure [15]. Also, water in an area without flowing away easily [10]. several efforts have been made to assess In most cases, the accumulation of such climate change induced flood risk both in abnormal large volume of water in an area that is developed and developing countries. Identifying not usually covered by water is also hampered the environmental factors inducing flood, the by poor percolation and runoff [10,11]. At the elements at risk as well as the strategies adopted global, national, regional and local scales, by the vulnerable population is particularly substantial evidence on the climate change essential in flood risk mitigation and contingency induced floods and flooding abound. planning [16]. Approximately 80% of the world’s population Key datasets common in climate change induced spread across just 15 nations which suffer from flood mapping include elevation, slope, aspect, severe impact of flooding annually. India, geology, distance from river, distance from road, Bangladesh and China topped the list while over distance from fault, soil type, land use and land 167,000 people in the United States of America cover, rainfall, normalized difference vegetation (USA) are exposed to flooding every year [12]. In index (NDVI), stream power index, topographic 9 Ibanga and Idehen; IJECC, 10(9): 8-23, 2020; Article no.IJECC.58768 wetness index, sediment transport index and inundated due to heavy rainfall and poor curvature [16-22]. Methodological frameworks drainage system in 2018 [29]. The 2019 flooding include socio-economic, biophysical, and affected the 36 states and over 124 LGAs integrated [23]. Manlosa and Valera [24] rendering 210,117 people vulnerable in addition deployed socio-economic approach to assess to 171 deaths while households were rendered micro scale flood damage in a Lakeshore homeless [30]. In Uhunmwonde Local Community of Jabonga in the province of Agusan Government Area (LGA), several households del Norte in the Philippines. It was found that were displaced leading to the establishment of monthly household income, land area farmed, temporary camp at Egor, the LGA headquarters. number of livestock owned, frequency of flood The 2020 rainfall prediction by the Nigeria incidence in the homes, flood velocity, and Meteorological Agency (NiMet) showed that the duration of inundation at the work area were the southern parts of Nigeria (where Edo State determinants of household flood vulnerability in including Uhunmwonde LGA is located) is the hazard zone. This study however neglected expected to have extended period of rainfall [31]. the roles of sociopolitical and environmental The implication of the 2020 rainfall forecast is variables in shaping societal vulnerability. increased probability of climate change induced flooding across the zone. Udo and Eyoh [25] also used biophysical approach to map river inundation and flood Thus, in order to avert the 2020 flood impact at hazard in Edo State. It was found that 25% were the present and in the future as well as to contain very high hazard zones while 30% of the state flooding, the Nigeria Hydrological Services was classified high hazard places. The lowly Agency (NIHSA) recommended measures such hazard areas covered 4354 square kilometers as flood sensitisation campaigns, flood risk (22.2%) and no hazard covered 8.2% of the mapping and flood vulnerability studies [29]. study area. Espada et al [26] used integrated Climate change induced food risk mapping in framework to assess the vulnerability of core Uhunmwonde LGA is