Abstract
The objective of this paper is to investigate the temporal trends of streamflow in the Lower Niger River Basin in Nigeria using Mann – Kendall (MK), Spearman’ rho (SP) and Thiel – Sen (TSA) non parametric tests at 5% of significant level. The effect of auto – correlation in the time series was eliminated using a Trend Free Pre – whitening (TFPW) approach .The results obtained show negative trends in annual maximum series and both deceasing and increasing trends in annual minimum series. The estimated slopes range -354.94£b£ -52.62m 3 /s/year and -0.92£b≤ 30m 3 /s/year for annual maximum and minimum series respectively. Both MK and SP tests showed consistent performance and ability in detection of trends at 5% significant level. The negative trends in streamflow combined with simultaneous decrease in rainfall and increase in air temperature are plausible evidence of climate change. Also, positive correlation between freshwater discharge and salinity intrusion into River Niger was observed. The combined effect of streamflow reduction and salinity intrusion will impact adversely on the agricultural potentials, water quality status and vegetation of the Lower Niger River Basin. Finally, this study recommends against construction of new reservoirs as this will exacerbate the observed negative trends, leading to unsustainable development. Keywords: Trend analysis, Climate change, Nigeria, Salinity intrusion, Mann – Kendall and Thiel – Sen Estimator. DOI : 10.7176/CER/11-4-02 Publication date :May 31 st 2019
Highlights
The availability and sustainable use of water resources is crucial for development and food security as well as economic development and livelihood of any nation
This study reported that climate change is clearly visible for mean discharges as well as for high and low floods
The main results of this study are summarized in Tables 4a. and 4b., containing the descriptive statistics, auto – correlation, Mann – Kendall, Spearman’s rho and Thiel –Sen estimator for annual maximum and minimum series.The time series with trend lines of annual maximum streamflow are presented in Figures 2a – j respectively
Summary
The availability and sustainable use of water resources is crucial for development and food security as well as economic development and livelihood of any nation. The status of water resources is a direct reflection of the climate factors on the drainage basin, any alteration of climatic characteristics will have direct impact on water availability. The potential impacts of climate change on hydrological extremes have been a major research concern in hydrology in the last two decades across the world. Most of these studies focused primarily on trend analysis of hydro climatic variables; precipitation, temperature and evapotranspiration( e.g., Oguntunde et al, 2011; Sonali and Kumar 2013; Oguntunde and Abiodun 2013; and Aich et al, 2016). Other publications deal explicitly on trends on streamflow( e.g. XU et al.,2014; Kahya and Kalayci 2004; and da Silva et al, 2015
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