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Efficient management of hydropower reservoir can only be realized when there is sufficient understanding of interactions existing between reservoir variables and energy generation. Reservoir inflow, storage, reservoir elevation, turbine release, net generating head, plant use coefficient, tail race level and evaporation losses are the major hydropower reservoir variables affecting the energy generation. Thus, this paper presents the modelling of reservoir variables of two hydropower dams along the River Niger (Kainji and Jebba dams) in Nigeria for energy generation using multilayer perceptron neural network. Total monthly historical data of Kainji and Jebba hydropower reservoirs' variables and energy generated were collected from Power Holding Company of Nigeria respectively for a period of (1970-2011) and (1984-2011) for the network training. These data were divided into training, testing and holdout data set. The neural network summary yielded a good forecast for Kainji and Jebba hydropower reservoirs with correlation coefficients of 0.89 and 0.77 respectively. These values of the correlation coefficient showed that the networks are reliable for modeling energy generation as a function of reservoir variables for future energy prediction.

Our study revealed periodicities of 2.3 and 2.25 years in wet and dry seasons and periodicities of 2 to 5 years on seasonal and annual timescales. Minimum temperature (Tmin), maximum temperature (Tmax) and evaporation recorded increases of 2.47, 1.37 and 28.37 %, respectively, but a reduction of 19.58 % in rainfall on decadal timescale. Periodicity of 8 to 12 years was also observed in annual Tmax. Cramer's test indicated a warming trend with significant Tmax increase in February, April, July, August, October and November during 2000-2009 on decadal monthly timescale, a significant decline in Summer rainfall but significant Tmax increase in Spring, Autumn and Winter on decadal seasonal timescale. The low correlation of rainfall with temperature parameters and evaporation indicates that advection of moisture into Lagos State seems to be the dominant mechanism controlling rainfall within the State alongside other tropical and extra-tropical factors. In addition, our study revealed that the persistent state of minimum temperature often precedes the arrival and reversal of the phase of maximum temperature. Furthermore, our study also revealed that extreme and high variable rainfalls, which are associated with the increased warming trend, had periodicities of 1 to 3 years with a probability of 86.45 % of occurring every 3 years between April and September. It is recommended that government and private sector should give financial and technical supports to climate researches in order to appropriately inform policy making to improve the adaptive capacity and resilience of Lagos State against climate change impacts and guard against maladaptation.

ABSTRACT; This paper presents the application of Mann-Kendall trend test and Standard Anomaly index onhydro-meteorological variables in the coastal area of Lagos state in order to determine the nature of trend and level of significance. The hydro-meteorological data such as air temperature, relative humidity, wind speed, rainfall and sea level rise were obtained from Nigeria meteorological agency (NIMET) Oshodi, Lagos. Variables such as rainfall, relative humidity, wind speed and sea level rise exhibited positive Kendall's (S) values indicate upward trend and imply an increase of the parameters over time. However, temperature showed negative Kendall's (S) which indicates downward trend and implies decrease over time. Sea level rise, rainfall, relative humidity and wind speed has mean statistics Zs of 3.9855, 1.9668, 3.0895 and 2.2553 respectively which are more than 1.96 (test statistics for a significant level of 5% that is (Z 0.025 =1.96), this implies that the upward trend is significance and there is tendency to continue. Temperature has statistic Zs of 0.0309 which is less than 1.96 and implies no significance, thus the reduction may not be noticed. The auto correlation factor values ranges from 0.59 to 0.99 for all the parameters, indicating a good fit. S tandard Anomaly index (SIA) results showed that trends for the temperature depicts downward trend with the slope of the trend equations are negative, this implies that temperature has tendency to decrease . Rainfall, relative humidity and sea level rise exhibited upward trend which implies tendency to increase. However, the mean wind speed exhibited upward trend while both maximum and minimum wind speed exhibited downward trend, but not noticeable. It can be inferred that both MannKendall trend test and standard anomaly index showed that there is tendency for trend increase in rainfall, humidity, windspeed and sea level rise, while temperature has tendency to decrease. This could be due to impact of climate variability which can influence flooding pattern in the coastline of Lagos State. ©JASEM

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