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TopBackground To The Study
The past two decades have seen a significant upsurge in the frequency of flooding on a global scale (Najibi & Devineni, 2017). The Intergovernmental Panel on Climate Change (IPCC) confirmed that flood vulnerability would most likely increase in line with increasing rainfall events (Conix & Bachus, 2007). The occurrence of flooding around the world is fast becoming a normality (Thomalla, Downing, Spanger-Siegfried, Han & Rockström, 2006) with about 70 million people exposed to flood risk and at least 800 million people susceptible (Peduzzi, Dao, Herold & Mouton, 2009). Its impacts are as well immeasurable. For example, in the United States, floods destroy property worth US$6 billion and kill 140 people annually (National Geographic, 2018).
In Nigeria, flooding is a recurrent phenomenon which could be coastal, fluvial or pluvial (Aderogba, 2012). Coastal and fluvial flooding in Nigeria affects coastal and riverine environments and are due to seasonal water upsurge from large rivers such as the Niger, Benue, Cross River, Kaduna, and others. On the other hand, pluvial floods are yearly occurrences during the rainy season (from July to October) and are more eminent in the cities (Nkwunonwo, Malcolm & Brian, 2015). Recent flood occurrences in Nigeria have been particularly, among other factors, geared by the release of water from the Lagdo Dam in Cameroon (Udo, Ojinnaka, Baywood & Gift, 2015), the high intensity of rainfall in some regions (Eagle Online, 2018) and the haphazard development of land on flood prone areas (Atufu & Holt, 2018).
Flooding is the most occurring natural hazard in Nigeria and the situation is dire (Aderogba, 2012). An early account of flooding in Nigeria is the Ogunpa River flooding of Ibadan in 1963, 1978, 1980 and 2011, which led to an estimated property loss of at least 30 billion naira and 100 fatalities. In Lagos, there were at least 8 flood events that killed at least 30 people between 2011 and 2012 (Komolafe, Adegboyega & Akinluyi, 2015). Whereas flooding has been a recurrent occurrence in Nigeria, the year 2012 event was a striking one, superseding previous flood events in the last 40 years. The National Emergency Management Agency (NEMA) reported that it affected 7 million people in 30 states, displaced 2.3 million people, killed 363 and cost Nigeria’s economy an estimated loss of US$ 9.6 billion (Amangabara & Obenade, 2015).
Earlier studies have examined flooding and flood-risk in Nigeria as a whole (Nkwunonwo, Malcolm & Brian, 2015; Komolafe, Adegboyega & Akinluyi, 2015), while others assessed the problem at a regional or state level (Amangabara & Obenade, 2015; Udo, Ojinnaka, Baywood & Gift, 2015; Udo & Eyoh, 2017, Efiong & Hogan, 2017). The question of “which Local Government Areas (LGAs) in Nigeria are most at risk to flooding and which are more vulnerable?” has however received no empirical attention. Providing answers to these questions are key to flood mitigation and adaptation in Nigeria and elsewhere. The geospatial technologies of remote sensing and geographic information systems (GIS) have proven to be of immense value in this regard.
GIS and remote sensing techniques have become indispensable tools for mapping flood-risk vulnerability (Karmakar, Simonovic, Peck & Black, 2010, Wicht & Osinska-Skotak, 2016; Das, Chattopadhya & Basu, 2017; Gandini, Prieto, Garmendia, San-Jose & Egusquiza, 2018), providing evidence for early warning and emergency response systems.