Satellite-based mitigation and adaptation scenarios for sea level rise in the lower Niger delta; Dissertation, UNESCO-IHE Institute for Water Education, Delft and TU Delft.

Accelerated sea level rise (SLR) is the most important climate change impact for coastal areas. The physical properties of deltas and anthropogenic activities make them vulnerable to the effects of the changing climate; however when evaluation of vulnerabilities is needed many coastal deltas lack necessary data for performing such a task. Leaving these coastal areas without adequate plans to combat sea level rise will cost vulnerable areas huge amounts of losses in lives and properties; e.g. as at 1995, it was estimated that in Nigeria alone, a no-response scenario will cost over $18billion in losses including an estimated 17,000km2 of wetland (Brown, Kebede, & Nicolls, 2011). Data availability is one of the most important factors for analysis, assessment and modelling of physical and other phenomena related to river and coastal systems. Consequently, to reduce the effects of SLR through adaptation and mitigation, the IPCC recommended that coastal areas collect data on physical, social and economic parameters e.g. topographical, land-use, population, tidal wave and range (Dronkers, et al., 1990). Many developing countries however lack measuring equipment and long-term records; Africa generally lacks long-term observational data to aid hydrological research (Niang, et al., 2014). Long-term shoreline dynamics of the Nigerian coastline for instance cannot be predicted since the available data is insufficient to even explain fluctuations during the last hundred years (Orupabo, 2008). The Niger delta has the highest sensitivity to climate change in Nigeria (it has a very gentle slope and low elevation) and its adaptive capacity is the second lowest in terms of socio- economic development of the country (FME, 2010). The Niger delta is also one of the coastal areas with little data for coastal planning and management, and consequently has poor availability of data for hydrologic and hydraulic modelling. Quantitative studies on the lower Niger delta have thus been limited by data availability and inaccessibility of parts of the delta (due to insecurity). Consequently, few quantitative studies using in situ data exist on the Niger delta; a quantitative study of the Niger delta by Awosika, et al., (1992) made use of aerial video data to estimate the cost of SLR and erosion losses for the Niger delta. However, subsequent studies by Ericson et al (2006), and Musa, et al., (2016) indicate that the area calculation by the study overestimated the extent of areas to be affected; thus, the value of losses might have been overestimated. Use of satellite data helps bridge the data gap by providing ancillary data (imagery, elevation, altimetry etc.) that can be used to quantify the effects of SLR on the Niger delta. This thesis uses satellite data and other auxiliary information as the main sources of data for hydrodynamic modelling and GIS analysis. This is a different approach as satellite data in water management and hydrology is normally used as a last resort and not the first point of choice since such data might not have the accuracy and precision of directly measured data. Studies have however shown that innovative methodologies by scientists have enabled better exploitation of satellite data to overcome the limitations and produce results with high correlation and manageable errors within present uncertainties (Musa, Popescu, & Mynett, A review of applications of satellite SAR, optical,altimetry and DEM data for surface water modelling, mapping and parameter estimation, 2015). This study aimed to assess the impact of SLR on the Niger delta land area, coastline, and surface water in an integrated way that will lead to practical recommendations for adaptation. Using projected global eustatic SLR values of 19mm by 2030 and 35mm by 2050 in addition to subsidence, this thesis estimated that relative SLR (RSLR) for the Niger delta will range from 0.14m– 0.44m by 2030, and 0.29m–0.96m by 2050. Using this RSLR values, the results show that a rise in sea levels of 0.14m already inundates areas in the Niger delta, and the flood extent increases with increase in SLR. Consequently, some 4.6–5.2% (viz. 1119.3–1254km2 ) of the Niger delta land area can be lost to inundation by 2030, and 4.9–6.8% (viz. 1175.9–1633km2 ) by 2050. Furthermore, the results indicate that without subsidence the inundation effect of SLR on the Niger delta will be minimal (since the eustatic values are just 19mm and 35mm by 2030 and 2050 respectively). Subsidence has therefore made the Niger delta very vulnerable to inundation by making the SLR values very high. Flooding in the lower Niger River will be affected by rise in sea levels especially as the area continues to subside (chapter 4). The effects include earlier occurrence of downstream flooding, increase in water depth and flooding of areas further upstream (than would occur without SLR). This increase in in flooding will be via expansion in lateral flooding extent in the downstream areas, but flooded areas will increase upstream because higher sea levels downstream will impede downward flow of flood waters which can result in a backwater effect and subsequent flooding of areas upstream. For the years without flooding from upstream, SLR will cause coastal areas downstream of the Niger River to flood earlier than usual. More so areas upstream of the Nun River, which remain dry in normal years, will get flooded when sea levels rise. SLR will increase the occurrence of coastal flooding (this is indicated by the flood generated by even the lowest level of rise in sea levels) because water levels and water depths will be higher (as shown for example in the Bonny River), thus increasing land area flooding extent. The flow velocity will also increase with SLR, and coastal floodwaters will thus be transported faster along the river to places upstream. Consequently, flooding of land areas at high tide will increase due to higher water levels. Furthermore, differences in flow velocity around narrow bends will also be higher with SLR than without, making river crossings more dangerous. A new coastal vulnerability index called coastal vulnerability index due to SLR (CVSLRI) was developed in this thesis. The CVSLRI evaluates coastline vulnerability due to SLR using 17 physical, social and human influence indicators of exposure, susceptibility and resilience (Chapter 5). The results showed that the variables that make a coastline highly vulnerable to SLR include (i) physical coastal properties, (ii) human influence, (iii) social properties. The reason being that human presence influences variables like coastal infrastructure and high population density, thus increasing the probability of damage to lives and property when a disaster occurs. More so, human interventions on coastal environments can affect sediment supply and accelerate erosion, and should therefore be captured in vulnerability assessments. Besides, the location of many settlements in remote areas, far away from the local government headquarters, reduces resilience to effects of SLR. The combination of these properties make coastal segments highly vulnerable to SLR. In conclusion, this thesis shows that parts of the Niger delta are highly vulnerable to effects of SLR due to high RSLR, and therefore need adequate mitigation/adaptation measures to protect them. Thus possible coastal mitigation/adaptation interventions for the Niger delta were modelled and studied. This thesis thus recommends that sustainable local resilience practices already being used in parts of the Niger delta should be included in adaptation planning. These include: planting of Bamboo trees for erosion control; using sandbags as bridges and dykes for flood control; using flood receptor pits as temporary flood water storage; and developing community legislation against sand mining and indiscriminate tree felling. In terms of major mitigation/adaptation interventions, measures that can be used for the lower Niger delta include: construction of dykes, by–pass channels, flood–pits (reservoirs), storm surge barriers, coastline shortening and legislation to ensure compliance by all. Furthermore, to effectively adjust to living with SLR in the Niger delta the following strategies should be adopted: building new structures raised on stilts; and changing farm practices to become more resilient