The study focused on rainfall anomalies and trend in Calabar as an imperative for human adaptation to climate change. Data on annual rainfall for the period of 100 years (1912-2011) and annual rainfall duration in days for the period 20 years (1992-2011) used for the study were obtained from the Nigerian Meteorological Agency (NIMET), Margaret Ekpo International Airport, Calabar. Data on the cost of buildings affected by flood incidence in the area for the period of 20 years (1992-2011) were obtained from the residents of the flood prone areas in Calabar. Trend line and spectral analysis were applied in identifying the trend and cycles of rainfall series in Calabar. The results revealed consistent fluctuations in rainfall pattern of Calabar for the past 100 years with a mean annual rainfall amount of 2949.300mm. The year 1927 and 2011 showed the highest departure from the mean with coefficient of variability 82 and 36 per cent respectively indicating the wettest years on record. On the other hand, the year 1973 was the driest year on record with the highest negative departure from the mean with a coefficient of variability 29 per cent. Furthermore, the spectral analysis gives dominant peaks at 7.0 and 25.0-31.0 years which indicated the relevant cycles of rainfall in Calabar. The results further showed that annual rainfall pattern of Calabar does not have a Gaussian distribution. The b value of 58.40 (or trend) was significant, indicating an increasing trend in annual rainfall in the study area during the period under study. Also, the annual rainfall intensity with beta coefficient of 0.437, contributes more to total cost of building loss to rainfall anomalies than annual rainfall duration, with beta coefficient of -0.063. Therefore, given the unstable nature of rainfall in Calabar, appropriate rainfall forecasting and early warning system should be made part and parcel of planning and developmental processes in order to reduce the cost of managing flood disaster in the area.
1.1 Background to the Study
The Earth’s climate is dynamic and varies on seasonal, decadal, centennial, and longer timescales. Each “up and down” fluctuation can lead to conditions which are warmer or colder, wetter or drier, more stormy or quiescent. These changes in climate are generally known as climate change. Climate change seems to be the foremost global challenge facing humans at the moment. World leaders, scientists, Non-governmental organizations (NGOs) and others who have shown concern have been meeting to find a lasting solution to this dilemma. The scientific community in particular has been trying to find the causes and solutions to climate change as its impact and consequences continue to be enormous. Climate change describes changes in the variability or average state of the atmosphere over time scales which may range from decades to millions of years (Adejuwon, 2004). It may be caused by natural processes or anthropogenic factors, especially human activities that load the atmosphere with Carbon and other greenhouse gases (Ekpoh, 2007).
Apart from global increase in temperature (global warming), some of the current and projected manifestation of climate change include: a rise in sea level, shifting of global climate zones, melting of polar ice, increased incidence and severity of extreme events, changes in the quality, duration and pattern of precipitation leading to increased drought, desertification and flooding. It can also result in a significant loss of food security, natural disasters, vanishing coastlines, human displacement, natural resource depletion, scarcity of safe drinking water, animal migration, pests management challenge, diseases and other health problems, loss of cultural practices and traditional ways of life, economic losses and energy crises, among others (IPPC, 2001a; Hulme 2001, & IPPC, 2007).
Furthermore, one of the major indicators of climate change especially in West African region is rainfall. Rainfall is the total amount of rain that falls in a particular area within a certain period of time. Rainfall is regarded as normal when it is within one standard deviation above or below the long term mean; otherwise it can be regarded as an anomaly rainfall (Ayoade, 2004). Using the study by Olaniran (2002)as an example, the normal or mean annual rainfall of Ilorin in Nigeria, based on 1971-2000 rainfall data of the area was 1200mm. Once this normal condition was established, any particular year at Ilorin could be described in terms of its departure from this normal. In effect, the 1530mm annual rainfall received at Ilorin in 1999 could be described as 27.5 per cent above normal while the 990.3mm annual rainfall received by the town in the year 2000 could be expressed as 17.5% below normal. These departures are referred to as anomalies. Rainfall trend on the other hand shows the pattern of the deviation over a given period. A persistent departure from the normal for example, above average rainfall of the same trend constitutes a climatic fluctuation. If the fluctuations persisted for along a time and were furthermore, statistically significant, then we might say, there had been a climatic change (Farmer and Wigley, 1985).
Episodes of rainfall anomaly can easily be traced to historical and contemporary times. For instance, the earliest recorded event of rainfall anomaly dates back to the biblical time of Noah about 4,000 years ago when it rained for 40 days and 40 nights with the resulting flood waters reaching 6m level and lasting 150 days. According to biblical account only Noah, his household and representatives of animals/birds collected by him, survived the prolonged and widespread flooding (Genesis, Chap. 7, verses 4-20). Oguntoyinbo, (1982) also cited the widespread famine of 1887 in southwestern Nigeria which was called ‘Iyan s’odi dogbun’ meaning ‘a famine which turned the moat into an impassable trench’ as well as a similar famine in the same area from 1903 – 1904 which was labeled ‘Iyan K’ehin S’ara’ meaning a famine which caused man to turn his back on his relations. Ekitiland experienced ‘Iyan f’owo re mi’ which means ‘famine in which life is saved by cash or cash survival famine’ from 1941-1944 (Olaniran, 2002). Incidents of famine, caused by drought, have also been reported in the history of events of Hausaland such as the Kakalaba famine of 1913-1914, the Yan Buhu famine of 1927 and Yar Gusau famine of 1942 (Thambyahpillay, 1979).
Within the contemporary times, we can also cite the Ilorin flood of October 19, 1976 which was preceded by one week of rainfall and which led to the submergence of 24 houses and evacuation of 50 others (Olaniran, 1983). Given the pervasive influence of floods in Ibadan in the 1960s and 1970s they became known, in the local parlance, as ‘omi ya’le, agbara ya sobu’ meaning that both residential and commercial areas are invaded by flood waters. Perhaps, the worst flood in the history of the town occurred on 31 August, 1980. This devastating flood was caused by prolonged and high intensity rainfall of 273mm in magnitude and it culminated in the loss of 300 lives. The property damaged was estimated then at N1.5 million (about N1.5 billion now) (Akintola, 1992). In 2011, flood from rainfall washed away 2,105 buildings in Ibadan, killed eight in Katsina, rendered 6000 families homeless in Sokoto and destroyed properties worth N10 billion in Lagos. Ibadan also experienced great damage in 2012 flood which resulted to the loss of many lives and displacement of many (Odufuwa, Adedeji, Oladesu & Bongwa (2012).
In Calabar, the changing pattern of rainfall is noticeable in the form of rainfall variability, which results in unpredictable changes in the frequency and intensity of extreme weather events such as floods and erosion. While the number of geophysical disasters has remained fairly steady, the number of hydro-meteorological disasters since 1996 has more than doubled. During the past decade over 90 percent of those affected by natural disasters are linked to hydro-meteorological event such as flood (Paredes, Trigo, Garcia-Herrera. & Franco, (2006)). The recent floods in the study area have highlighted how important it is to analyze the trends in the rainfall regime of this area. This is because of its effects on the city’s population, environment and socio-economic activities. Increasing flood risk is now being recognized as the most important sectorial threat from climate change in most parts of the world. This has prompted public debate on the apparent increased frequency of extreme, and in particular, on perceived increases in rainfall intensities.
The usefulness of the analysis of changing pattern of rainfall and the frequency of intense rainfall in Calabar lies in predicting the severity of flood events within the city. This is because the years with severe flood menace could coincide roughly with exceptionally high rainfall totals. As observed by Udosen (2008), intense soil erosion and flood hazards occurred in Akwa Ibom State in 1977. The same year contrast remarkably with other years in terms of its high rainfall total of 3855 mm. This study is therefore an attempt to evaluate rainfall anomaly and trend in Calabar.
1.2 Statement of the Research Problem
Rainfall is one of the key climatic elements of Calabar, because crops, animals and indeed humans derive their water resources largely from rainfall. It is considered as the main determinant of the types of crops that can be grown in the area and also the period of cultivation of such crops and the farming systems practiced. Statistical evidence from the Nigerian Meteorological Agency (NIMET), Calabar (2011), shows that the mean annual rainfall for Calabar based on 1912-2011 rainfall data of the area is 2949.300mm. However in 1912, Calabar recorded a mean rainfall amount of 2377.95mm, 10 years later in 1921, a mean rainfall amount of 2468.12mm was recorded and 3405.38mm in 1931. Also in 1941, our weather data shows that the area recorded a mean rainfall amount of 3516.88mm, 2938.53mm in 1951 and 2532.13mm of mean rainfall in 1961. Furthermore, in 1971, the data shows a mean rainfall amount of 3234.69mm, 2733.80mm in 1981, 2661.90mm in 1991, 3202.00mm in 2001 and a total of 4002.80mm of rainfall in 2011. Available data went further to show that the mean total rainfall for the years 1912-1941 (30 years) is 3041.92mm, for the period 1942-1971 the mean total rainfall is 2923.40mm while between the years 1971-2001 Calabar received a mean total rainfall of 2871.68mm (NIMET, 2011). These coefficients only approximates annual average values but does not express vividly the deviation from the long term average either up or down the normal curve. Whereas, each “up and down” fluctuation can lead to conditions which are warmer or colder, wetter or drier. For instance, while individual annual total rainfall in a 100 years rainfall series may look stable in terms of runoff within the city, the deviations from the long term mean might show continuous increases with runoff and discharges overwhelming the drains which were designed to cope with normal rainfall in the area.
Consequently, Calabar have suffered from severe floods in recent times. Indeed, the climate of the area has become highly unpredictable, making many people to wonder what has happened to the climate. For instance, available records of flood disaster occurrence and impact in the area reveals that in 2009, a total 1,567 buildings were being affected by flooding, displacing about 12,333 people and destroying properties worth millions of naira in Calabar. The records further reveal that in 2010, a total of 955 buildings were being affected by flood with the displacement of about 8,197 people and household properties worth millions of naira lost. In the same vein, the 2011 floods in Calabar, was devastating, because it overwhelmed the drains, which were designed to cope with only normal rainfall. The floods of 2011 resulted in major disasters with over 3,986 buildings in Calabar and its suburbs being overtaken by flood, rendering over 30,359 persons homeless and washing away several urban farmlands, disrupting socio-economic activities, displacing people, and causing damage to properties worth millions of naira (State Emergency Management Agency (SEMA), Calabar, Oct. 2012).
Invariably, with further significant variations in the rainfall characteristics of the area, it is important that scientific studies be undertaken so as to provide the society with accurate information on the real and potential impacts of extreme climatic variability, as well as, the mitigation and adaptation options available. At this time when the world is grappling with diverse environmental problems including global warming, ozone depletion, acid rain, killer hurricanes, destructive thunderstorms, droughts and major flood episodes, efforts at finding explanations to these problems should be of great importance, since the environmental, social and economic cost of managing extreme climatic variability is bound to be enormous from the standpoint of society and policy makers (Ekpoh, 2011).
On the basis of the foregoing, the response of the inhabitants of Calabar to the spatio-temporal environmental and socio-economic implications of rainfall anomalies have not been given adequate attention and academic scrutiny in the area under investigation; this may be due to lack of adequate information in this regard. This study therefore seeks to bridge this gap in knowledge by examining rainfall anomalies and trend in the study area. From the foregoing, the following research questions are posed to guide the study;
(i) What are the annual rainfall anomalies of Calabar in the past 100 years.
(ii) What is the trend in the annual rainfall anomalies of Calabar.
(iii) What is the annual rainfall recurrence interval in the area.
(iv) Does rainfall regime impact on buildings in Calabar.
(v) How are the people of the area coping with the impact of rainfall anomalies in the area.
1.3 Aim and Objectives of the Study
The aim of the study is to examine rainfall anomalies and trend as an imperative for human adaptation to climate change in the area. The specific objectives are as follows;
(1) To examine annual rainfall anomalies of Calabar for the period 1912-2011 (100 years rainfall series).
(2) To examine the trend in the annual rainfall anomalies for Calabar using same 100 years (1912-2011) annual rainfall data.
(3) To assess the annual rainfall probability in the area using the 100 years rainfall data.
(4) To examine the impact of the rainfall regime on buildings in Calabar for the period 1992-2011 (20 years).
(5) To make recommendations towards adapting to the implications of rainfall anomalies in Calabar.
1.4 Hypothesis of the study
In line with the objectives of the study, the following hypotheses are postulated such as:
H1: The annual rainfall series of Calabar does not have a Gaussian (normal) distribution.
H1: There is a significant change in annual rainfall trend in Calabar for the period 1912-2011.
H1: Flood resulting from rainfall has a significant impact on building loss in Calabar for the period 1992-2011.
1.5 Scope of the study
This research is restricted to the city of Calabar which comprises Calabar Municipality and Calabar South Local Government Areas. The analysis restricted to 100 years (1912-2011) annual rainfall data drawn from archives of NIMET Calabar. This rainfall climatology study of Calabar involved the analysis and determination of the series, averages, deviation from averages, extremities, probability assessment as well as relationships.
1.6 Relevance of the study
This research will attempt to identify episodes of rainfall inconsistencies and expose the trend in rainfall behavior in the area. It will help us understand the likely causes of extreme event such as flood in the area. It will also help in ascertaining the vulnerability of the inhabitants of the area to rainfall variability.
Furthermore, possible adaptations to the problem of rainfall extremities shall be proffered as it may help in cushioning the continuous calamities caused by climate change in the area. The study will also enhance runoff discharge prediction and the design of drains and buildings in the area, as it will afford us the opportunity of predicting mean rainfall values as well as the likely impact on building and drainage channels in the area.
The study will also furnish the political class/leaders, administrators and policy makers with facts that will guide them in the formulation of policies towards adapting to the problems of climate change in the area. It is hoped that this research work will serve as a reference work for future studies as well as understanding of climatic variability in the area and Cross River State in general.
1.7 Study area
1.7.1 Location and size
Calabar is the capital of Cross River State. It is located at the Southern part of Cross River State (FIG. 1). It lies between longitudes 8017’00’’E and 8020’00’’E latitudes 4050’00’’N and 5010’00’’N. Calabar metropolis comprises of Calabar Municipality and Calabar South Local Government Areas and covers an area of about 274.593 Sq km. Calabar is bounded to the north by Odukpani Local Government Area and to the East by Akpabuyo Local Government Area (Fig.1.1). Calabar is located between the Great Kwa River to the East and the Calabar River to the West. The present of urban area is on the eastern bank of the Calabar River. Its growth to the south is hindered by the mangrove swamps.
FIG.1 Cross River State showing Calabar (Study area)
Source: Geographic Information System (GIS) Laboratory, Department of Geography and Environmental Science, University of Calabar.
Calabar falls within tropical equatorial (Af) climate with high temperature, high relative humidity and abundant annual rainfall (Oguntoyimbo, 1978; Inyang, 1980). Two major air masses affect the climate of Calabar as well as other contiguous locations in the West African region. The Tropical Maritime (mT) and the tropical continental (cT) air masses affect the climate in two distinct seasons. mT air prevails and influences its moisture characteristic while the cT air influences the dry season condition due to is desert source across the two air masses at the upper troposphere from east to west. This is called the Equatorial Esterlies (EE). The two air masses meet at the pressure front called Inter Tropical discontinuity (ITD) (Oguntoyimbo, 1978).
Insolation effect is quite high caused by the sheer factors of its tropical location as well as the activities of urban development which have significantly altered the land cover. Rainfall is of the double maxima (double peak) regime with important peaks in July and September depending on the yearly weather cycles. Rainfall duration spans over 9-10 months of the year but is somewhat sporadic during the dry season. Dry season commences from November through February and is heralded by the southward moving air mass from the Saharan-high pressure belt. The dry season weather or the harmattan season produces depression due to the cool-dry temperature and moisture characteristics of the cT air. It transports Aeolian deposits (aveoli) from its source in the Sahara. This incidence produces hazy weather which reduces visibility and also cuts down insolation. Presently, over-grazing and deforestation have caused the impact of harmattan wind to be felt beyond the latitude of Calabar (Inyang, 1980).
Inyang’s study (1980) identified four thermal zones in Calabar which coincided with areal differences in population density, incidence of hydrologic/topographic influence on the heat distribution. The main areas include the Mbukpa-Eldgerley complex, the Watt market axis, the central depression (in the area around the State Housing Estate) and the Calabar River Basin.
According to Inyang (1980), study on the peculiarity of its climatic regime. The mean annual was given as 21.60C, while minimum was 22.70C. Also, the daily range of temperature was given as 3.80C. The highest temperature values are recorded in February and March. Relative humidity is high all year round with the lowest value of 76.8 recorded in February and the highest recorded in August with a value of 92 percent.
Fabgemi and Okulaja (1971) in their climatic classification of Nigeria based on the space correlation technique, categorized Calabar under the zone ‘A’ rainfall category with “wet and moist’ conditions, and a monsoonal pattern of rainfall. Thorthwarte and Matter (1955),Papadaski (1961) devised a similar technique where Calabar was identified under the per humid climatic zone with a moisture index of 100.
Udo (1970) categorized Calabar and other eastern state in his regional delimitation of Nigeria under the Cross River Basin. This Basin is a trough or depression which extends from the lower Benue plains to the Atlantic shores on the Gulf of Guinea. It is flanked by the eastern Borderland to the east and the Udi/Nsukka ceusta to the west (Ofomata, 1975). It encloses several states such as Cross River, Anambra, Ebonyi, Abia, Imo, Akwa Ibom and Enugu.
Petters et al (1995) described this landscape formation as belonging to the old Benue Basin around the cretaceous period of oceanic transgression in Nigeria. Ekwueme (1990 and 1995) grouped the Calabar formation into two categories. These are the cretaceous sedimentary formation and the Basement complex (igneous) formation. The cretaceous formation is conformal with the complex which appears in the area around Odukpani. The Bende-Ameke formation could also be found through a contagious deposit from Onitsha through Umuahia to Calabar. This formation is a litoral equivalence of the Ijebu formation in western Nigerian (Ofomata, 1975). Predominant soil categories here are of the coastal plain sands.
In terms of relief pattern, the city is hilly and undulating in most areas. It has a gentle slope which varies in some areas from zero percent to about 20 percent in others. Elevated grounds are predominant in the east with prominently north-south trending orientation. This elevation separates the eastern plateau from the more or less western ridge (Inyang, 1980).
1.7.4 Relief of Calabar
The Calabar Flank sedimentary basin that extends from the southern margin of the is Oban Basement complex to the boundary with the e Niger Delta. Here, sudden sediment thickening e demarcates the Niger Delta Basin that formed as the latest of a series of basins in the Benue Trough, diagonally crossing Nigeria from the southwest to ir the northwest. Northwest-southern trending basement structures underlie the Calabar Flank and e define the ltu High and the lkang Trough, thus relating the Calabar Flank to the South Atlantic Cretaceous marginal basins with similar horst-and-graben structures in Angola and Gabon (Murat (1972). The sedimentary succession on the Calabar Flank is mostly of Cretaceous age, comprising an ancient river-borne sandstone, the Awi Formation; and the overlying marine Odukpani Group of Albian to Late Cretaceous age Murat (1972).
The Odukpani Group comprises the Mfamosing Limestone, the Ekenkpon Shale and the New Netim Marl, which :h are all exposed near the Odukpani local government area headquarters. This is unconformably covered by the Nkporo Shale. Tertiary marine shales and regressive sandstones overlie the Cretaceous succession. The total sediment thickness in the surfaces of the Calabar Flank is over 3500m Nyong (1995).
The area is regarded as a low lying land which washes its sediment into the Qua River. Although the most significant feature present in the are is Great Qua River. The relief has a characteristically elevated coastal margin in areas around Marina road but lower in areas around Anantigha in Qua River lower valley Nyong (1995).
The unique characteristics of high humidity, high rainfall and temperature have culminated to a highly unique, complex and diverse flora and fauna. The predominant vegetation type is mangrove. The mangrove flora consists of trees and shrubs of few general varying species. The common genus is Rhizophora with three: R racemosa, R harisonii and R. mangle. The dominant feature of mangrove is the stilt roots of Rhizophora species. Associated with these species are Avicennia africana and Lagunculeria racemosa. There are also palms, Prodococcus bateri, Ancistrophyllum opacum and the gregarious and aggressive Nypa frutican. Salt marshes and sea grasses interact with the mangrove forest to support the entire coastal zone. Hence, because of its status of composition and structure it is known to be part of the most complex vegetation which is the northernmost limits of the Mangrove growth in the Cross River estuary (Ukpong 1995)
This complex plant community of wetland origin formed an ecological niche for reptiles, monkeys, birds, fishes, shrimps, mollusks, and other wildlife. Thus, it is often harvested for wood, fuelwood, tannin, leaves, fibers and dyes. Mangrove environment in particular is important for inland fisheries, serving as highly productive habitat for shell and finfish. These inform the migration of fishermen from Delta, Akwa Ibom and Akpabuyo to settle and take advantage of the rich supply at this point (Ukpong, 2007).
1.7.6 Population and socio-economic activities
The population of Calabar during the pre-colonial era was estimated at about 10,000. By the census figures of 1963 the population of Calabar was 99,352, and in 1991, it was 328,876 (Nigerian population census, 1991), an increase of 3 per cent within 28 years (and percentage total growth of 5.5 from 1987-1997). In 2006, the population of Calabar grew to 371,022 (Nigerian Population census, 2006), through immigration from the rural areas into Calabar in search of better opportunities. The population growth of Calabar has been followed by the expansion of its physical boundaries. This increase in the physical boundaries implies a corresponding loss of vegetation and land in the area thereby a direct impact on the micro-climate. This fact has been attested to by Ekanem (1980), who asserted that “Calabar has within the span of a decade (1967-1997) been transformed into a booming administrative, commercial, and political nucleus in the state’’.
Presently, Calabar is the economic and political nerve center of Cross River State, and the headquarters of Calabar Municipality and Calabar South Local Government Areas. With its recent designation as a tourism destination in West Africa, Calabar has witnessed unprecedented influx of people from within and without its boundaries which has necessitated the building of service structures such as hotels, transportation lines, commercial, industrial and residential areas. According to Atu (2010), the new status of Calabar has also brought industries such as the Tinapa Business and Leisure Resort, the Export Processing Zone (EPZ), Dangote Mills, Unicem Factory, Niger Mills and a host of other business and commercial activities such as banks, hotels and fast food joints. This development is not without repercussions on the natural environment as lands that were formally vegetated, used for agriculture and as habitat for biodiversity are now being used for residential, commercial and industrial purposes to accommodate the growing population and businesses. For instance, Atu (2010), reports that 127.10 ha of agricultural land that was formerly used for cultivation of oil palm are now growing residential houses instead of palm trees and the new secretariat complex is standing on over 50 ha of land formerly used for the cultivation of vegetables. The loss of once vegetated land implies a corresponding alteration of the micro-climate of the area which in turn has great impact on the long term climatic averages of the area.