1 ARMA Modelling of Benue River Flow Dynamics: Comparative Study of PAR Model

The seemingly complex nature of river flow and the significant variability it exhibits in both time and space, have largely led to the development and application of the stochastic process concept for its modelling, forecasting, and other ancillary purposes. Towards this end, in this study, attempt was made at stochastic modelling of the daily streamflow process of the Benue River. In this regard, Autoregressive Moving Average (ARMA) models and its derivative, the Periodic Autoregressive (PAR) model were developed and used for forecasting. Comparative forecast performances of the different models indicate that despite the shortcomings associated with univariate time series, reliable forecasts can be obtained for lead times, 1 to 5 day-ahead. The forecast results also showed that the traditional ARMA model could not robustly simulate high flow regimes unlike the periodic AR (PAR). Thus, for proper understanding of the dynamics of the river flow and its management, especially, flood defense, in the light of this study, the traditional ARMA models may not be suitable since they do not allow for real-time appraisal. To account for seasonal variations, PAR models should be used in forecasting the streamflow processes of the Benue River. However, since almost all mechanisms involved in the river flow processes present some degree of nonlinearity thus, how appropriate the stochastic process might be for every flow series may be called to question

Rainfall Variability and Trend Analysis over Lokoja, Nigeria

Studies on rainfall variability and trends are of great importance, particularly to the nations where rainfed agriculture is predominant. This study used CRU data (CRU_TS 4.01) to examine the temporal variability of rainfall data over Lokoja. Statistical tests were employed to examine variability and trend in monthly, seasonal and annual time series. Analysis of variability showed that the rainy seasons and annual rainfall had less variability (CV 30) in some months in the rainy season (April, July and August). Standardised precipitation index showed alternation of wet and dry period conditions had been witnessed in the study area. Trend analysis showed more positive trends had been experienced from 1970 through 2010. The variability in rainfall and the increasing trend may have a tremendous effect on water resources availabilities and vulnerabilities of Lokoja

PROJECTED EXTREME RAINFALL INDICES IN GUINEA AND SUDANO-SAHELIAN ECOLOGICAL ZONES, NIGERIA

Drought and Flood episodes are twin issues that are consequences of extreme rainfall events. The negative impact of extreme rainfall events makes understanding their behaviour under the future climate change necessary for regional planning. Hence, the objective of the study is to project extreme rainfall indices in Guinea and Sudano-Sahelian ecological zones, Nigeria. A set of four extreme rainfall indices namely: maximum 5-day rainfall (Rx5day), heavy rainfall days (R10mm), consecutive wet days (CWD) and consecutive dry days (CDD) were adopted. The data and computation were done using KNMI Climate Explorer. Projections were produced for the near-term 2019-2048, mid-term 2049-2078 and long-term 2079-2100 periods with reference to the 1959-1988 and 1989-2018 baselines. The multi-model ensemble mean of couple model intercomparison project 5 (CMIP5) under representative concentration pathways (RCPs) 2.6, 4.5, and 8.5 were used. Mann-Kendal statistical test was adopted to analyze the trends in extreme rainfall indices at the 0.05 significance level. Based on the results, it can be deduced that there is a significant positive trend in the whole Guinea and Sudano-Sahelian ecological zone as a region for maximum 5-day rainfall with respect to all the three RCPs. As for heavy rainfall, itreveals that there is no significant positive trend for RCP2.6 with respect to the three projected periods under consideration but significant positive trends with respect to 2049-2078 for RCP4.5 as well as RCP8.5 with respect to 2049-2078 and 2079-2100 periods. Increase in CDD, as well as a decrease in CWD, were both not significant at the 0.05 confidence level. Therefore, it is expected that this study will aid guidance to the understanding of the ongoing changes as well as possible changes in rainfall and rainfall-related extremes. It is also important for future planning of water resources management and agriculture in Guinea and Sudano-Sahelian ecological zones of Nigeria. KEYWORDS: Extreme rainfall indices, Guinea, Sudano-Sahelian, Ecological zones, Nigeri

Parametric Linear Stochastic Modelling of Benue River flow Process

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Rainfall Variability and Trend Analysis over Lokoja, Nigeria

Studies on rainfall variability and trends are of great importance, particularly to the nations where rainfed agriculture is predominant. This study used CRU data (CRU_TS 4.01) to examine the temporal variability of rainfall data over Lokoja. Statistical tests were employed to examine variability and trend in monthly, seasonal and annual time series. Analysis of variability showed that the rainy seasons and annual rainfall had less variability (CV < 20), but the variability was high (CV > 30) in some months in the rainy season (April, July and August). Standardised precipitation index showed alternation of wet and dry period conditions had been witnessed in the study area. Trend analysis showed more positive trends had been experienced from 1970 through 2010. The variability in rainfall and the increasing trend may have a tremendous effect on water resources availabilities and vulnerabilities of Lokoja

MAIZE YIELD RESPONSE TO RESIDUAL SOIL MOISTURE

Two sets of experiments were conducted in three replicates each on both upper and lower fringes of Minna inland valley, Niger State, Nigeria. While the upper fringe was subjected to surface irrigation the residual moisture in the lower fringe provided the maize crop with all water requirements from planting to maturity. Randomized Complete Block Design was utilized for the study. The results showed that the actual maize yield obtained in plots 1, 2 and 3 on the upper fringe were 100.15 kg/ha, 180.45 kg/ha and 200.45kg/ha, respectively, whereas 168.78 kg/ha, 240.16 kg/ha and 271.20 kg/ha were recorded in the lower fringe for similar plot conditions. The difference in means of the maize yield grown under irrigation and residual moisture were statistically insignificant at 5% and 1% levels of significance