Understanding Climate Variability and Rainfall Distribution Patterns in Osogbo, Southwestern Nigeria
DOI:
https://doi.org/10.62292/10.62292/njp.v34i2.2025.397Keywords:
Rainfall Variability, Precipitation Concentration Index (PCI), Rainfall Variability Index (RVI), Climate ChangeAbstract
Understanding rainfall variability and distribution is critical for climate adaptation, agricultural planning, and water resource management, particularly in tropical regions like Nigeria. This study analyses the temporal variability and distribution of rainfall in Osogbo, Southwestern Nigeria, over a 34-year period (1990–2023) using the Rainfall Variability Index (RVI) and the Precipitation Concentration Index (PCI). RVI was employed to quantify interannual rainfall anomalies and classify drought intensities, while PCI assessed the seasonal distribution of rainfall across annual, dry, and wet periods. Results from the RVI revealed a near-balanced pattern of rainfall anomalies, with 53% of the years showing below-average rainfall and 47% above average. Drought classification showed that 76% of the years experienced no drought, while 24% ranged from moderate to extreme drought conditions. Dry season analysis indicated higher variability, with a predominance of irregular and strongly irregular rainfall distribution (PCI > 16) in 85% of the years, suggesting unseasonal or erratic rainfall events. In contrast, the wet season exhibited more stable and uniform rainfall patterns, with 74% of the years showing PCI values below 10, indicating favourable conditions for rain-fed agriculture. The findings underscore increasing rainfall unpredictability, particularly during the dry season, and highlight the growing need for climate-resilient agricultural practices, improved seasonal forecasting, and integrated water management strategies. This study contributes to the understanding of local-scale climate behaviour and supports evidence-based decision-making in the face of climate variability and change.
Downloads
References
Adefolalu, D. O. (1986). Rainfall trends in Nigeria. Theoretical and Applied Climatology, 37, 205–219.
Adejuwon, S. A. (2006). Food crop production in Nigeria II: Potential effects of climate change. Climatic Research, 32(2), 229–245. https://doi.org/10.3354/cr032229
Akinsanola, A. A., & Zhou, W. (2019). Projections of West African summer monsoon rainfall using CMIP6 models. Climate Dynamics, 53(7), 4393–4409.
Alimi, S. A., Andongma, T. W., Ogungbade, O., Senbore, S. S., Alepa, V. C., Akinlabi, O. J., Olawale, L. O., & Muhammed, Q. O. (2022). Flood vulnerable zones mapping using geospatial techniques: Case study of Osogbo Metropolis, Nigeria. THE EGYPTIAN JOURNAL OF REMOTE SENSING AND SPACE SCIENCES, 25(3), 841–850. https://doi.org/10.1016/j.ejrs.2022.08.005
Agnew C.T. and Chappel A. (1999). Drought in the Sahel. GeoJournal 48:299–311
Animashaun, I. M., Oguntunde, P. G., Akinwumiju, A. S., & Olubanjo, O. O. (2020). Rainfall analysis over the Niger Central hydrological area, Nigeria: Variability, trend, and change point detection. SCIENTIFIC AFRICAN, 8, e00419. https://doi.org/10.1016/j.sciaf.2020.e00419
Atedhor, G. O., Ojeh, V. N., & Uriri, A. E. (2019). Spatio-temporal variability of rainfall and temperature in the Lower Niger River Basin. Theoretical and Applied Climatology, 137, 231–244.
Ayanlade, A., Odjugo, P. A. O., & Adebayo, T. S. (2019). ANALYSIS OF RECENT CHANGES IN RAINFALL AND DROUGHT INDICES IN NIGERIA, 1981–2015. International Journal of Climatology, 39(10), 3702–3717. https://doi.org/10.1080/02626667.2019.1673396
Ayoade, J. O. (1983). Introduction to Climatology for the Tropics. Ibadan: Spectrum Books.
De Luis M, González-Hidalgo JC, Brunetti M, Longares LA (2011) Precipitation concentration changes in Spain 1946–2005. Nat Hazard 11(5):1259–1265
Ezenwaji, E. E., Nzoiwu, C. P., & Chima, G. N. (2020). Analysis of precipitation concentration index (PCI) for Awka urban area, Nigeria. HYDROLOGY: CURRENT RESEARCH, 11(3), 100041.
Grist, J. P., Nicholson, S. E., & Barcilon, A. I. (2002). A study of the dynamic factors influencing the rainfall variability in the West African Sahel. JOURNAL OF CLIMATE, 15(7), 1377–1397
Hare, F.K. (1983). Climate and desertification. World Meteorological Organization Technical Note No. 268.
Ibitoye M. O. and Okende F. (2016). A GIS-Based Assessment of Potable Water Network Distribution in Osogbo, Nigeria. Ife Research Publications in Geography, 14,17- 29
IPCC (2021). Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the IPCC.
Nicholson, S. E. (2009). A revised picture of the structure of the “monsoon” and land ITCZ over West Africa. CLIMATIC DYNAMICS, 32, 1155–1171.
Nicholson, S.E. (2013). The West African Sahel: A review of recent studies on the rainfall regime and its interannual variability. ISRN Meteorology, 2013, Article ID 453521.
NIMET (2011). Nigeria Climate Review Bulletin, 2011. Nigerian Meteorological Agency.
Njoku Onyema, O., & Onugwu, A. C. (2023). Study of Rainfall Distribution Pattern Changes and their Relationship with Atmospheric Parameters at Enugu and Kano States using Regression Model. Nigerian Journal of Physics, 32(3), 16-25.
Njoku, C. A., Ojeh, V. N., Naabil, E., Ekwe, M. C., Joshua, M. M., Elijah, E., & Malgwi, M. W. (2023). Analysis of rainfall trend and variability in Lagos, Southwestern Nigeria. In J. C. Egbueri, J. O. Ighalo, & C. B. Pande (Eds.), CLIMATE CHANGE IMPACTS ON NIGERIA (pp. 115–134). Springer Climate. https://doi.org/10.1007/978-3-031-21007-5_7
NPC National Population Commission (2006). Nigerian population census report 2006
Odekunle, T. O. (2004). Rainfall and the length of the growing season in Nigeria. International Journal of Climatology, 24(4), 467–479.
Odekunle, T. O., Balogun, E. E., & Ogunjobi, K. O. (2008). On the prediction of rainfall onset and retreat dates in Nigeria. Theoretical and Applied Climatology, 91(1), 93–105.
Oladipo, E. O. (1993). Some aspects of drought in Northern Nigeria. Natural Hazards, 8(2), 171–188.
Olaniran, O. J. (2002). Rainfall anomalies in Nigeria: The contemporary understanding. Nigerian Geographical Journal, 3(1), 11–22.
Olaniran, O. J., & Sumner, G. N. (1989). A study of climatic variability in Nigeria based on the onset, retreat, and length of the rainy season. International Journal of Climatology, 9(3), 253–269.
Oliver, J. E. (1980). Monthly precipitation distribution: A comparative index. The Professional Geographer, 32(3), 300–309.
Omotosho, J. B., Balogun, A. A., & Ogunjobi, K. (2000). Predicting monthly and seasonal rainfall in West Africa using a statistical weather model. INTERNATIONAL JOURNAL OF CLIMATOLOGY, 20(8), 865–880
Peel, M. C., Finlayson, B. L., & McMahon, T. A. (2007). Updated world map of the Köppen–Geiger climate classification. Hydrology and Earth System Sciences, 11(5), 1633–1644. https://doi.org/10.5194/hess-11-1633-2007 , 2007.
Zhang K, Yao Y, Qian X, Wang J (2019). Various characteristics of precipitation concentration index and its cause analysis in China between 1960 and 2016. Int J Climatol 2019:1–11.