Analele Universităţii din Oradea, Seria Geografie Year XXVI, no. 2/2016 (December), pp. 188-200 ISSN 1221-1273, E-ISSN 2065-3409 Article no. 262109-715 SEA LEVEL RISE AND ITS POTENTIAL IMPACTS ON COASTAL URBAN AREA: A CASE OF ETI-OSA, NIGERIA Ayodele Michael AGBOOLA Department of Geography, Obafemi Awolowo University, Ile-Ife, Nigeria, e-mail: [email protected] Ayansina AYANLADE Department of Geography, Obafemi Awolowo University, Ile-Ife, Nigeria, e-mail: [email protected] Abstract: This study examines the spatial extent of coastal urban development and its potential sensitivity to sea-level rise. The main aim of the study is to critically examine the extent of growth in Eti-Osa over time, and the potential impacts of sea leve rise. Landsat Enhanced Thematic Mapper Plus (ETM+) imageries of years 2000 and 2015 were used to evaluate the different land use type identified. Post-classification change detection method was used to evaluate the output of the maximum likelihood supervised classification analysis done. This was also used to estimate the changes induces through urban development on the environment which accounts for the biodiversity loss. ASTER GDEM 2 imagery of 2011 was used to generate the elevation data used for the inundation analysis. Thus, both Land use map of Eti-Osa in 2015 and the down scaled Sea-level rise scenarios (at 0.5 to 15 meters) were used for the inundation mapping. Results obtained from this research affirms that indeed Eti- Osa has been subjected to gross urban expansion giving room for diverse forms of environmental degradation among which are huge replacement of natural land cover with built-up, reclamation of wetlands and sand filling of water bodies. This basically illustrates growth but also the risk that accompanies the advent of excessive alteration of natural ecosystem as Sea-level rise projections imply in this research. Key words: Sea-level rise, Urban Development, impacts assessment, * * * * * * INTRODUCTION Sea-level rise poses a major threat to most lands along the coast and also major developments having direct access to the shoreline especially in cities and other forms of development within the low-lying area around the coast (McGranahan et al, 2007). This is evident by the forecast concerning Global Mean Sea-level Rise by Intergovernmental Panel for Climate Change (IPCC, 2007), there is a projection that by the year 2020, about 75 to 250 million people would encounter the challenge of increased water (flooding) through climate change. A rise in sea- level usually increase the flooding depth and extend the area that stays wet in the dry season (Brammer, 2013). Furthermore, according to the climate change report by IPCC (2007), towards Corresponding Author http://istgeorelint.uoradea.ro/Reviste/Anale/anale.htm Sea Level Rise and its Potential Impacts on Costal Urban Area… 189 the end of the 21st century, the low-lying coastal areas with large population would face the challenge of Sea-level Rise and it would cost between 5-10% of Gross Domestic Product (GDP) for adaptation (IPCC, 2007). Studies have reported that the situation will be aggravated by the high rate of land subsidence (Syvitski et al., 2009), and rapid rate of coastal erosion (Vidal, 2013a, b). As peculiar to Lagos metropolis, Nwokoro and Dekolo (2012) examined that 1.31% of the total water body in Lagos within the period of study has been lost to the collective effort of continuous land reclamation and sand filling of wetland to cater for the need for residential development either by the government or private developers. These findings summed up together to imply that the urban dwellers settled along the coast and developments might be helpless against rise in sea-level. The vulnerability of the Lagos coastline to Sea-level Rise is particularly exacerbated by its low- lying, densely populated nature, a high concentration of GDP generating industries and infrastructures especially along the barrier lagoon Coast of Lagos-Badagry-Seme border of the southwestern part of Nigeria (Odunuga et al., 2014). Urban centers experience huge rate of urban expansion as a result of diverse factors among which are population growth and human desires (Adesoji, 2011). The observed rate of urbanization comes with enormous physical developments such that the interaction between urban developments and natural state of the environment has gone far beyond equilibrium (Bai, 2001). The growing trend of urbanization in the society has induced a high degree of depletion on the environment thus, the present level of degradation of the environment (Odewaye, 2009). Lagos state has been a typical urban center to experience rapid urban development in a bit to cater for the pressing need for housing facilities and other infrastructures to support adequate livelihood conditions. The ever-increasing demand for physical developments has therefore resulted in both coordinated and uncoordinated developments leading to little or no consideration for physical planning standards. There is, therefore, intense intrusion into the natural habitat which is supposed to be conserved to aid a balance in the ecosystem (Oduwaye, 2009; Ogundele et al., 2011). As a result of the economic influence of the coastal cities as in the case of Eti-Osa in Lagos, it aids coastal population and commercial activities which are projected to also increase (Jongman et al., 2012). Hence, there has been a lot of challenges from hazardous human activities such as excessive exploitation of natural resources, biodiversity loss, depletion of natural habitat and coastal erosion (Arthurton et al., 2006; Diop et al., 2011). Consequently, coastal urban planning is faced with the challenge of adequately putting land into use to meet the demand for urban growth, equity and sustainability even at the expense of the limited nature of the habitable land. The critical concern is the inability of the concerned institutes to keep up with the pace of urban expansion and densification. The nature and potential vulnerability of coastal urban centers to inundation as an effort of Sea-level Rise (SLR) are considered as one of the measures for environmental degradation. The projected Sea-level Rise and climate change are a pressure that should enhance the speedy preparation for national planning that would be implemented to safeguard, maintain and accelerate economic and social development in the country so as to meet the corresponding growing population and its vulnerability to existing environmental hazards (Brammer, 2010). Hence, sustainable adaptation requires institutions that can negotiate and address the demands made of an ever-changing landscape in ways that are just and legitimate, so that the institutions of planning, as well as communities at risk, are able to persist over time. Successful adaptation must therefore, be sustainable, both in terms of its ability to ensure “socially and environmentally sustainable development pathways, including both social justice and environmental integrity” (Reiksen et al., 2011). A number of modeling approaches that have been used to evaluate the potential impact of sea-level rise have been critically appraised. This has availed a number of limitations and challenges such as coarse resolution levels for landscape-scale models and low confidence in site- specific model simulations. Thus, Elevation-based analysis is however identified to be of high effectiveness (Bo et al., 2010) owing to the fact that it has a very simple procedure and is effective 190 Ayodele Michael AGBOOLA, Ayansina AYANLADE if the appropriate data and maps are put to use in the assessment of the possible effect of inundation resulting from proposed Sea-level Rise (CCSP, 2009). The elevation-based analysis in this study entails the generation of digital elevation model (DEM), adoption of sea-level scenarios, and performing inundation spatial analysis. STUDY AREA Lagos is the second fastest growing coastal urban community in Africa which is economically buoyant such that urban growth and development experiences a surge within a short time. Eti-Osa, the study area is thus a prominent division of Lagos that experiences a relatively large communal expansion and hub of most large structured commercial functions of Lagos as a result of its proximity to the coast (Atlantic Ocean). The Study area lies approximately between 60 26' 20'' N to 60 27' 50'' N and longitudes 30 24' 10'' E to 30 40' 10'' E (figure 1) which covers about 180.54 km2 in land area. In Eti-Osa, a tropical climate is observed with a varying wet and dry season such with an average temperature of 28 oC annually. The wet (rainy) season has been observed to have two peaks usually May to July and September to October. As a result of diverse urban developments, several natural patterns have mostly been altered as such that land reclamation from the sea has added to the total land area. Furthermore, Eti-Osa stretches from Magrigo canal at Obalende through into Lagos lagoon and crosses the lagoon to the back of Sabokoji Island behind the port at Amuwo Odofin. Eti-Osa shares a boundary with 3 local governments namely Lagos Island local, Amuwo Odofin and Apapa. Figure 1. Maps of the study area: Nigeria (A), Lagos State (B) and Eti-Osa (C) METHOD Data Preparation and pre-processing Landsat ETM+ (2000) and OLI (2015) images of Eti-Osa were acquired from the United State Geological Survey archive and are said to have been prepared in WGS 1984 (UTM Zone 31) coordinate system. This is considered most suitable for all processing and analytical functions in this study, thus image registration and atmospheric corrections were not done again. The ASTER GDEM 2 satellite imagery which was used to generate the digital elevation model and Landsat Sea Level Rise and its Potential Impacts on Costal Urban Area… 191 imageries acquired were both subset to extract the region of interest. This was to extract the study area using the administrative boundary information (Shape-file).