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A Monthly Double-Blind Peer Reviewed Refereed Open Access International e-Journal -Included in the International Serial Directories Assessment of Rainfall Variation and Trends in Calabar for the period 1982-2011

A Monthly Double-Blind Peer Reviewed Refereed Open Access International e-Journal -Included in the International Serial Directories Assessment of Rainfall Variation and Trends in Calabar for the period 1982-2011
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    IJPSS   Volume 3, Issue 11   ISSN: 2249-5894    __________________________________________________________   A Monthly Double-Blind Peer Reviewed Refereed Open Access International e-Journal - Included in the International Serial Directories Indexed & Listed at: Ulrich's Periodicals Directory ©, U.S.A., Open J-Gage, India  as well as in Cabell’s Directories of Publishing Opportunities, U.S.A.   International Journal of Physical and Social Sciences   http://www.ijmra.us   96     November 2013  Assessment of Rainfall Variation and Trends in Calabar for the period 1982 2011 I . A. Ekpe   A. I. Afangideh* R. A. Offiong* Abstract The study examines the variation and trend of rainfall in Calabar for the period 1982-2011. Rainfall data for the study were collected from the Nigerian Meteorological Agency (NIMET),Margaret Ekpo International Airport, Calabar. Statistical techniques such as mean, standard deviation, standardized anomaly, coefficient of variation (CV) and Time Series Charts with Trend line analysis(smoothen with 5-years running mean)were used to depict the temporal variation of rainfall in Calabar. Furthermore, spectral analysis was also used to determine the periodicities of rainfall for Calabar using the 30 years (1982-2011) rainfall data. The result shows that the mean annual rainfall for the period of study over Calabar was found to be 2917.72 mm. The study also shows that 2011was the wettest year, while 1983 was revealed to be the most rainfall deficit year. When a 5 year running mean was put through the annual total rainfall series fluctuations involving increasing trend were most prominent in the periods 1986  –   2001 and 2006  –   2011. A fluctuation involving decreasing rainfall trend was only prominent in the period 2001  –   2006. Significant at 95%, the spectral analysis results gives dominant peaks at 3.9 years and 8.1 years, indicating the significant cycles of rainfall for the past 30 years in Calabar. Keywords: Rainfall Variation and Trend, Spectral Analysis, Time Series Analysis, Rainfall Cycles, Calabar.    Dept. of Geo. & Environmental Science University of Calabar, Nigeria    IJPSS   Volume 3, Issue 11   ISSN: 2249-5894    __________________________________________________________   A Monthly Double-Blind Peer Reviewed Refereed Open Access International e-Journal - Included in the International Serial Directories Indexed & Listed at: Ulrich's Periodicals Directory ©, U.S.A., Open J-Gage, India  as well as in Cabell’s Directories of Publishing Opportunities, U.S.A.   International Journal of Physical and Social Sciences   http://www.ijmra.us   97     November 2013  INTRODUCTION Rainfall is the total amount of rain that falls in a particular area within a certain period of time.Rainfall is one of the key climatic elements, 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. Also, being blessed with abundant freshwater swamps and watersheds, rainfall serves as a major means of recharge of these water sources in Calabar. However, amidst these numerous benefits derived from rainfall, available statistics from Nigerian Meteorological agency (NIMET), Calabar shows mark variation of rainfall in the area over the past years, with its negative ills which pose great threats to human life, properties and urban agriculture within the city. 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 (Cross River 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    IJPSS   Volume 3, Issue 11   ISSN: 2249-5894    __________________________________________________________   A Monthly Double-Blind Peer Reviewed Refereed Open Access International e-Journal - Included in the International Serial Directories Indexed & Listed at: Ulrich's Periodicals Directory ©, U.S.A., Open J-Gage, India  as well as in Cabell’s Directories of Publishing Opportunities, U.S.A.   International Journal of Physical and Social Sciences   http://www.ijmra.us   98     November 2013  and economic cost of managing extreme climatic variability is bound to be enormous from the standpoint of society and policy makers (Ekpoh, 2011). Studies for changes in annual mean precipitation have been realized in several parts of the world. For instance, a steep decrease of the precipitation in 1970 has been identified in parts of Bulgaria and Romania (Adger , Hug , Brown, Conway , Hulme 2003). Several authors have analyzed hydro-meteorological time series in West Africa from Niger to Senegal (Le Barbe , Lebel , Tapsoba 2002). They pointed out the non-stationarity of the series and suggest a climatic  jump down between 1965 and 1972, the majority of the shifts appearing between 1969 and 1970. Precipitation in the Great Plains of the United States of America also showed a significant change with an increase since the late 60´s, the last two decades being the wettest of the 20th century (Novotny and Sfefan (2007). The Brazilian Amazon basin precipitation records showed a shift near 1975, downward in the northern area and upward in the southern part (Marengo, 1999). The Sahel is characterized by strong climatic variations and an irregular rainfall that ranges between 200mm and 600 mm with coefficients of variation ranging from 15 to 30% (Fox and Rockström, 2003; Kandji et al., 2006). According to IPCC, a rainfall decrease of 29-49% has been observed in the 1968-1997 period compared to the 1931-1960 baseline period within the Sahel region (McCarthy et al., 2001). The West Africa region has experienced a marked decline in rainfall from 15 to 30% depending on the area (Niasse, 2005). The trend was abruptly interrupted by a return of adequate rainfall conditions in 1994. This was considered to be the wettest year of the past 30 and was thought to perhaps indicate the end of the drought. Unfortunately, dry conditions returned after 1994 (McCarthy et al., 2001). In the study of Ogolo and Adeyemi (2009), on the variations and trends of some meteorological parameters at Ibadan, they discovered that the downward trend in rainfall of 1988-1990 in Ibadan was interrupted by sharp increases between 1991 and 1993 to an above yearly average. This was followed by a drought year in 1994 where annual rainfall amount dropped to the minimum. Between 1995 and 1997, rainfall amount in this station follow an increasing trend. The years 1988, 1991, 1993, and 1995-1997 have been identified as years of above yearly average rainfall, while the years 1989, 1990, 1992 and 1994 are years of near and below yearly average rainfall.    IJPSS   Volume 3, Issue 11   ISSN: 2249-5894    __________________________________________________________   A Monthly Double-Blind Peer Reviewed Refereed Open Access International e-Journal - Included in the International Serial Directories Indexed & Listed at: Ulrich's Periodicals Directory ©, U.S.A., Open J-Gage, India  as well as in Cabell’s Directories of Publishing Opportunities, U.S.A.   International Journal of Physical and Social Sciences   http://www.ijmra.us   99     November 2013  This study therefore seeks to examine the variation and trends in rainfall over Calabar for the period 1982 to 2011 (30-year). The following objectives were employed in this work to achieve this aim such as: (i)   To examine the annual rainfall variation in Calabar for the period 1982-2011 (ii)   To examine the trends in rainfall of the area for the period 1982-2011 (iii)To determine the periodicities of rainfall in Calabar for the period 1982-2011 MATERIALS AND METHOD Study Area Calabar is the capital of Cross River State. It is located at the Southern part of Cross River State as seen in Fig.1, Calabar is located between longitudes 8 0 17’00’’E and 8 0 20’00’’E latitudes 4 0 50’00’’N and 5 0 10’00’’N. Calabar metropolis comprises of Calabar Municipality and Calabar South Local Government Areas and covers an area of about 1,480 Sq km. As depicted in Fig.1 Calabar is sandwiched 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. 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). There have been a massive development and urban expansion in the area over the last 10 years. 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.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.    IJPSS   Volume 3, Issue 11   ISSN: 2249-5894    __________________________________________________________   A Monthly Double-Blind Peer Reviewed Refereed Open Access International e-Journal - Included in the International Serial Directories Indexed & Listed at: Ulrich's Periodicals Directory ©, U.S.A., Open J-Gage, India  as well as in Cabell’s Directories of Publishing Opportunities, U.S.A.   International Journal of Physical and Social Sciences   http://www.ijmra.us   100     November 2013  Types of Data and Source The data required for this work was annual rainfall values over Calabar for the months January to December from 1982 to 2011. The data covers annual amounts for a period of 30 years (1982-2011).The data for this study was obtained mainly through secondary sources from the records section of the Nigerian Meteorological Agency, Margaret Ekpo international Airport, Calabar. Techniques and Procedure The purposive sampling technique was used for data collection. The measurement of rainfall is done by removing the funnel and emptying the collected rain in the bottle/container into a graduated cylinder with a 3.8 cm (1.5 inches) diameter. The reading is done at eye-level to an accuracy of 0.25 mm (0.01 inch). Data analysis Statistical and graphical tools in Microsoft Office Excel were primarily employed in the analysis and presentation of this study. These consist of the following: (a)   Time series with trend lines analysis of the annual rainfall values to illustrate the trend pattern in rainfall behavior. (b)   The spectral analysis applied in identifying the cycles of rainfall series in Calabar for the study period (1982-2011). The spectral analysis is used to analyze cycles of precipitation data. The power spectra of annual, seasonal and monthly anomalies were analyzed using the autocorrelation spectral analysis  –   ASA (Blackman and Tukey, 1958; WMO, 1966).The ASA is obtained by applying the discrete Fourier transform (DFT) algorithm to the correlation functions derived from the time series, taking as a smoothing function a Turkey- Hamming window (Padmanabhan, 1991). This was done using the spss software window. (c)   Standardized anomaly chart. (d)   Descriptive statistical analysis   (e)   ) = ( ) Where; x = the variable N = the number of years
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