Trend Analysis of Precipitation in Some Selected Stations in Anambra State

A. Ifeka, A. Akinbobola^*

Department of Meteorology, Federal University of Technology, Akure, Nigeria.

DOI: 10.4236/acs.2015.51001                

Abstract

State is in the South East geopolitical zone of Nigeria. The major occupation of the people in this region is trading and farming, which depends on rainfall and other climatic factors. This paper presents statistical and trend analyses of the rainfall in some selected stations in Anambra State, which includes Ifite-Ogwari, Awka, Onitsha and Ihiala. Rainfall data for a period of 1971-2010 were obtained from Climate Research Unit (CRU). The existence of trend and statistical analyses was conducted on monthly total rainfalls using non-parametric techniques. The study revealed that overall averages of yearly and monthly total rainfall were 5798.78 mm and 1739.62 mm in Ifite-Ogwari, 6051.8 mm and 1815 mm in Awka, 6288.87 mm and 1886.88 mm in Onitsha, and 6637.19 mm and 1997.1 mm in Ihiala. Yearly total rainfall has Mann-Whitney of 26 and 41 between 1971 and 1990, 1991 and 2010 respectively in Ifite-Ogwari, 32 and 42 between 1971 and 1990, 1991 and 2010 respectively in Awka, 42 and 39 between 1971 and 1990, 1991 and 2010 respectively in Onitsha, and 33 and 45 between 1971 and 1990, 1991 and 2010 respectively in Ihiala. These parameters show that there are significant trends in the rainfall in term of yearly total for the period. Sen’s estimator revealed that there were significant downward trends for yearly total (-0.775 mm/year) and (-0.094 mm/year) within the period of 1971-1990 and 1991-2010 in Ifite-Ogwari. There was an upward trend of yearly total (1.841 mm/year) between 1971 and1990, whereas there was a downward trend of yearly total (-0.211) between 1991 and 2010 in Awka. It was concluded that there was a significant downward trend in the yearly total and mean rainfalls in Ifite-Ogwari, Awka, Onitsha and Ihiala in the last four decades (40 years), which could be attributed to climate change.

Keywords

Precipitation, Trend Analysis, Non-Parametric Tests

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	Osborn, T.J., Hulme, M., Jones, P.D. and Basnett, T.A. (2000) Observed Trends in the Daily Intensity of United Kingdom Precipitation. International Journal Climatology, 20, 347-364. http://dx.doi.org/10.1002/(SICI)1097-0088(20000330)20:4<347::AID-JOC475>3.0.CO;2-C
[2]	Ventur, F., Rossi Pisa, P. and Ardizzoni, E. (2002) Temperature and Precipitation Trends in Bologna (Italy) from 1952 to 1999. Atmospheric Research, 61, 203-214. http://dx.doi.org/10.1016/S0169-8095(01)00135-1
[3]	Lettenmaier, D.P., Wood, E.F. and Wallis, J.R. (1994) Hydro-Climatological Trends in the Continental United States, 1948-88. Journal of Climate, 7, 586-607. http://dx.doi.org/10.1175/1520-0442(1994)007<0586:HCTITC>2.0.CO;2
[4]	Turkes, M. (1996) Spatial and Temporal Analysis of Annual Rainfall Variations in Turkey. International Journal of Climatology, 16, 1057-1076. http://dx.doi.org/10.1002/(SICI)1097-0088(199609)16:9<1057::AID-JOC75>3.0.CO;2-D
[5]	Zhang, X., Vincent, L.A., Hogg, W.D. and Nitsoo, A. (2000) Temperature and Precipitation Trends in Canada during the 20th Century. Atmospheric Ocean, 38, 395-429. http://dx.doi.org/10.1080/07055900.2000.9649654
[6]	Mosmann, V., Castro, A., Fraile, R., Dessens, J. and Sanchez, J.L. (2004) Detection of Statistically Significant Trends in the Summer Precipitation of Mainland Spain. Journal of Atmospheric, 70, 43-53.
[7]	Partal, T. and Kahya, E. (2006) Trend Analysis in Turkish Precipitation Data. Hydrological Processes, 20, 2011-2026. http://dx.doi.org/10.1002/hyp.5993
[8]	National Bureau of Statistics (2011) Annual Abstract of Statistics 2011. 27.
[9]	Wikipedia (2014) Anambra State. http://en.wikipedia.org/wiki/Anambra_State
[10]	NIMET (2014) 2014 Seasonal Rainfall Prediction (SRP). S & E Consulting, Scottsdale, 9-15.
[11]	Kahya, E. and Kalayci, S. (2004) Trend Analysis of Stream Flow in Turkey. Journal of Hydrology, 289, 128-144. http://dx.doi.org/10.1016/j.jhydrol.2003.11.006
[12]	Burn, D.H. and Elnur, M. (2002) Detection of Hydrological Trends and Variability. Journal of Hydrology, 255, 107-122. http://dx.doi.org/10.1016/S0022-1694(01)00514-5
[13]	Loveday, R. (1980) Statistics. A Second Course in Statistics. 2nd Edition, Cambridge University Press, Cambridge.
[14]	Guttman, I., Wilks, S.S. and Hunter, J.S. (1971) Introductory Engineering Statistics. 2nd Edition, John Wiley and Sons Inc, New York.
[15]	Sen, P.K. (1968) Estimates of the Regression Coefficient Based on Kendall’s Tau. Journal of the American Statistical Association, 63, 1379-1389. http://dx.doi.org/10.1080/01621459.1968.10480934