Exploring temporal hydroclimatic variability in the Niger Basin (1901–2006) using observed and gridded data

Abstract

Hydroclimatic variability manifests as abrupt shifts, trends, runs, and recurrent cyclical phenomena, collectively referred to as components. In this article, we tested for the presence and magnitude of each component in the Niger Basin (West Africa), using the 0.5 ∘ by 0.5 ∘ gridded annual rainfall and temperature data produced by the Climate Research Unit (CRU) at the University of East Anglia, UK, for the period 1901-2006. The streamflow data was also analysed for different sub-basins of the Niger Basin. Abrupt shifts were tested using a Bayesian and nonparametric approach. Trends were analysed using the Mann-Kendall trend test. Runs were extracted for dry, neutral, and wet conditions, simulated 1000 times based on the skew normal distribution, and used to investigate various run characteristics. Cyclical behaviour was investigated using continuous wavelet analysis. The results show that an abrupt change point occurred in 1969 in the rainfall and streamflow (but not temperature) time series in all subwatersheds of the Niger Basin. The magnitude of the shift in the mean rainfall varied between 16 and 24%. The temperature time series exhibit strong positive trends in all watersheds. Post change point, the rainfall and streamflow time series show positive, though statistically non-significant trends at = 0.1. In contrast, disregarding the change point, all subwatersheds show significant negative trends at = 0.05 and the maximum run lengths are about 4 years long for both dry and wet conditions. Finally, wavelet analysis showed that both rainfall and streamflow in the Niger Basin fluctuate on cycles that are predominantly 2-4 years long, with a few occurrences in the 6-8 years range. Wavelet activity diminished noticeably when a series appeared strongly dominated by trends. The results provide a more comprehensive view of climatic variability than would be obtained from only one or a few components.

Phenology-Based Biomass Estimation to Support Rangeland Management in Semi-Arid Environments

“…The rangelands of Niger are mainly located in the Sahel zone, a semi-arid region between the Sahara desert in the north and the Sudanian savannah in the south and are highly vulnerable as a result of the high inter-annual precipitation variability [3,4] and, hence, rangeland production variability. In addition to the inter-annual weather variability, the Sahel region of Niger shows great spatial precipitation heterogeneity, making rangeland production highly variable in space in a single year.…”

Biomass estimation to support pasture management in Niger

“…Pastoral production systems are mainly located in the Sahelian part of the country which is very vulnerable due to the high inter-annual rainfall variability (e.g., Nicholson, 2013 and references therein;Tarhule et al, 2014) and hence pasture production. Besides the temporal variability, the region is also characterised by a high spatial rainfall variability, increasing the need for a better management of the transhumance movements.…”

Time Series Analysis of Floods across the Niger River Basin

“…In the Sahelian and Benue regions, the mean rainfall during this period was approximately 35% lower compared to the period before 1970. This dry period is followed by a return to wetter conditions in West Africa (e.g., [14,15]). During the return to a wet phase, the annual precipitation up to 2012 did not exceed values that had been measured during the 1960s.…”

“…For the Benue region, no time series was long enough for the analysis. In order to avoid the complex distributions of the whole time series that change their directions several times, the analysis was limited to the period after the changepoint around 1970 which was identified by the changepoint analysis in all regions and also by Tarhule et al [15]. For the comparison of trends of AMAX, annual precipitation and heavy precipitation, the period from 1979-2012 is used since the used WFDEI data is available only for this period and due to the absolute differences of the data set, it is not possible to use WFD and WFDEI complementarily.…”

“…Jury [14] analyzed streamflow trends in Africa, including one station in the NRB (Niamey), and found an increase in streamflow that matched their general finding of a "return to wet conditions" in Africa in recent decades. Tarhule et al [15] analyzed the hydroclimatic variability between 1901 and 2006 in the NRB, and found a general changepoint in the year 1969, after which both rainfall and streamflow time series show a positive trend in the NRB, confirming the wetting trend. Pouyard et al [16] described the spatial and temporal variability of the water balance in the region by analyzing the relation of rainfall and runoff in small to large catchments.…”