CHARACTERISATION OF SPATIO-TEMPORAL PATTERN OF RAINFALL AND TEMPERATURE OVER THE LOWER NIGER RIVER BASIN

Abstract

The regional climate has been changing with attendant physical, social and environmental consequences culminating in extreme like flood, drought and other climate related hazards. Rainfall and temperature (maximum and minimum) plays fundamental role in agricultural development of Lower Niger River Basin and indeed Nigeria. In view of this, temporal rainfall and temperature patterns over the Lower Niger River Basin (LNRB) was examined. Thirty-five years (1979-2013) of rainfall and temperature time series data from six synoptic stations within the Basin was obtained from Lower Niger River Basin Development Authority, (LNRBDA) Ilorin. Analysis carried out includes Descriptive, homogeneity, autocorrelation, potential trend and spatial variability. Standardized anomaly was employed to determine the anomaly in rainfall and temperature. Similarly, regionalization of the Basin was done using the Principal Component Analysis (PCA) and K-Clustering Analysis to determine major modes of variability and partitioned to find the coherent zones within the Basin. From the result, mean annual rainfall ranges from 1120.5 mm to 1780.6 mm. Time series data analysis revealed homogeneity of rainfall and inhomogeneity in maximum and minimum temperature except at Oke Oyi station. There was positive autocorrelation across the Basin at lag1 = 0.301153 < 2 at Ganaga and was least at Oke Oyi in maximum and minimum temperature. Trend analysis was carried out using Mann-Kendall in annual and monthly bases, though the annual result showed statistically insignificant trend across the Basin in rainfall, maximum and minimum temperature. Monthly Mann-Kendall revealed marked variability in some months that were significant. The spatial variability of rainfall revealed Ekirin Ade having the highest in annual and seasonal times. The standardized anomaly showed marked transition in temperature regime; specifically, characterised by changing from colder than normal to warmer than normal conditions. The last decades depicted 80% colder than normal while the last fifteen years showed 90% warmer than normal. The anomaly result revealed 55% more rain, 41% Little Dry Spell and 4% normal within the last 35 years. The year to year variation that contributed to the anomalies were 34.68, 13.24 and 16% for maximum, minimum and rainfall. This increase portends a disturbing signal which could result in evaporation, heat related hazards and consequently extreme hazards associated with flooding and drought. Based on the regionalization analysis, using PCA and K-means Clustering, the result showed that the entire Basin is one coherent homogeneous zone. An understanding of this implication is central to Agricultural food security, water resources planning and management, and help to simplify the larger analysis of water budget.