Performance of the Global Forecast System's medium-range precipitation forecasts in the Niger river basin using multiple satellite-based products

Accurate weather forecast information has the potential to improve water resources management, energy, and agriculture. This study evaluates the accuracy of medium-range (1–15 d) precipitation forecasts from the Global Forecast System (GFS) over watersheds of eight major dams (Selingue Dam, Markala Dam, Goronyo Dam, Bakolori Dam, Kainji Dam, Jebba Dam, Dadin Kowa Dam, and Lagdo Dam) in the Niger river basin using NASA's Integrated Multi-satellitE Retrievals (IMERG) Final Run merged satellite gauge rainfall observations. The results indicate that the accuracy of GFS forecast varies depending on climatic regime, lead time, accumulation timescale, and spatial scale. The GFS forecast has large overestimation bias in the Guinea region of the basin (wet climatic regime), moderate overestimation bias in the Savannah region (moderately wet climatic regime), but has no bias in the Sahel region (dry climate). Averaging the forecasts at coarser spatial scales leads to increased forecast accuracy. For daily rainfall forecasts, the performance of GFS is very low for almost all watersheds, except for Markala and Kainji dams, both of which have much larger watershed areas compared to the other watersheds. Averaging the forecasts at longer timescales also leads to increased forecast accuracy. The GFS forecasts, at 15 d accumulation timescale, have better performance but tend to overestimate high rain rates. Additionally, the performance assessment of two other satellite products was conducted using IMERG Final estimates as reference. The Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS) merged satellite gauge product has similar rainfall characteristics to IMERG Final, indicating the robustness of IMERG Final. The IMERG Early Run satellite-only rainfall product is biased in the dry Sahel region; however, in the wet Guinea and Savannah regions, IMERG Early Run outperforms GFS in terms of bias.

The Biology of the African Bonytongue Heterotis niloticus (Cuvier, 1829) from the Lower Niger River at Agenebode in Edo State, Nigeria

Background. The African bonytongue, Heterotis niloticus, is readily accommodated in the fresh water of the Niger River. It is available all year round with a large population of juveniles and adults due to its fast growth and versatile feeding habits. This commercial fish is a highly preferred source of food because of its high protein content and hardy flesh, thus forming a very important component in the diet of many Nigerians. It is highly valued because of its socioeconomic importance and benefits. Hence, this research is designed with the aim of studying the biology of the African bonytongue, Heterotis niloticus, and providing viable information about its importance in fish culture in order to make an available added variety of culturable and affordable fish species in Nigeria. Results. The oesophagus is a muscular organ that is short and distensible. The oesophagus leads to the gizzard-like stomach, a reddish bilobed organ that is muscular and tough. H. niloticus is an omnivorous macrophage detritor, consuming a wide variety of bottom-dwelling food items. The histology of the gastrointestinal tract reveals four conspicuous layers from the inside to the outside: mucosa, submucosa, inner circular layer and outer longitudinal layer of muscularis, and serosa. The presence of numerous mucus glands and longitudinal folds with a prominent columnar epithelium provides durable length or an extension of the gut mucus to aid lubrication and easy passage of food materials, protecting the mucosal epithelium from mechanical or chemical injuries arising from interactions with digestive tract contents or enzymes. In addition, the presence of absorptive cells helps in the absorption of valuable nutritive substances. Conclusions. The anatomy of the mouth and gut and the aforementioned histology are modified to accommodate the feeding habits. H. niloticus has a single ovary that rests on the right side of the fish; it is reproductively active as the flood plains rise and peaks at the peak of the rains, being a moderately fecund fish. The high fecundity is complemented with peaks of GSI observed during the months of September, October, and November, which reveals spawning periods. Hence, the aforementioned attributes of H. niloticus make the fish a viable fish species for culture.

Future Climate Change Impacts on River Discharge Seasonality for Selected West African River Basins

The changing climate is a concern to sustainable water resources. This study examined climate change impacts on river discharge seasonality in two West African river basins; the Niger river basin and the Hadejia-Jama’are Komadugu-Yobe Basin (HJKYB). The basins have their gauges located within Nigeria and cover the major climatic settings. Here, we set up and validated the hyper resolution global hydrological model PCR-GLOBWB for these rivers. Time series plots as well five performance evaluation metrics such as Kling–Gupta efficiency (KGE),); the ratio of RMSE-observations standard deviation (RSR); per cent bias (PBIAS); the Nash–Sutcliffe Efficiency criteria (NSE); and, the coefficient of determination (r2), were employed to verify the PCR-GLOBWB simulation capability. The validation results showed from satisfactory to very good on individual rivers as specified by PBIAS (−25 to 0.8), NSE (from 0.6 to 0.8), RSR (from 0.62 to 0.4), r2 (from 0.62 to 0.88), and KGE (from 0.69 to 0.88) respectively. The impact assessment was performed by driving the model with climate projections from five global climate models for the representative concentration pathways (RCPs) 4.5 and 8.5. We examined the median and range of expected changes in seasonal discharge in the far future (2070–2099). Our results show that the impacts of climate change cause a reduction in discharge volume at the beginning of the high flow period and an increase in discharge towards the ending of the high flow period relative to the historical period across the selected rivers. In the Niger river basin, at the Lokoja gauge, projected decreases added up to 512 m3/s under RCP 4.5 (June to July) and 3652 m3/s under RCP 8.5 (June to August). The three chosen gauges at the HJKYB also showed similar impacts. At the Gashua gauge, discharge volume increased by 371 m3/s (RCP8.5) and 191 m3/s (RCP4.5) from August to November. At the Bunga gauge, a reduction/increase of -91 m3/s/+84 m3/s (RCP 8.5) and -40 m3/s/+31 m3/s/(RCP 4.5) from June to July/August to October was simulated. While at the Wudil gauge, a reduction/increase in discharge volumes of −39/+133 m3/s (RCP8.5) and −40/133 m3/s (RCP 4.5) from June to August/September to December is projected. This decrease is explained by a delayed start of the rainy season. In all four rivers, projected river discharge seasonality is amplified under the high-end emission scenario (RCP8.5). This finding supports the potential advantages of reduced greenhouse gas emissions for the seasonal river discharge regime. Our study is anticipated to provide useful information to policymakers and river basin development authorities, leading to improved water management schemes within the context of changing climate and increasing need for agricultural expansion.

Evidence of an Eleventh-Century AD Cola Nitida Trade into the Middle Niger Region

Kola nut (Cola cf. nitida) and Safou fruit (Dacryodes edulis) remains have been discovered in eleventh- to fourteenth-century archaeological contexts at Togu Missiri near Ségou in Mali. These remains are evidence of early trade in perishable foodstuffs from the West African forest zone into the Middle Niger region. On the basis of these finds, this paper argues that long-distance trade links were well established by the end of the first millennium AD. It thereby supports the hypothesis that dates the inception of trade between the West African forest zone and the savanna regions to the first millennium AD. The circumstances of the find are discussed, as are the implications for our understanding of the wider exchange network based on the Niger River system in the late first and early second millennium CE.

Breeding performance and embryogenic development of three strains of Heterobranchus longifilis in Nigeria

Summary The study sought to investigate the chronology of events and timing of embryogenesis, as well as breeding performances of three strains of Heterobranchus longifilis from Nigeria. Fish samples were collected from Benue River in Makurdi, Niger River in Onitsha, and Rima River in Sokoto for this study. Induced spawning of the strains was carried out so that egg development could be tracked from fertilization to hatching using a simple microscope. The microphotographs obtained showed that the embryogenesis of the strains followed a similar pattern to those of other members of the family Clariidae, however with changes occurring in the specific timing of the sequences of events (i.e. interstrain and interspecies differences). When the different strains were compared, the study noted similarities (P > 0.05) in the overall breeding performance (except for fertilization rate), survival at different stages of development, timing of embryogenesis, and larvae characteristics. The outcomes of this study, therefore, provide baseline information on what genetic improvement of the species through strain crossing can be attempted in future studies.

Recent Changes in Hydroclimatic Patterns over Medium Niger River Basins at the Origin of the 2020 Flood in Niamey (Niger)

Niamey, the capital of Niger, is particularly prone to floods, since it is on the banks of the Niger River, which in its middle basin has two flood peaks: one in summer (the red flood) and one in winter (the black flood). In 2020, the Niger River in Niamey reached its all-time highest levels following an abundant rainy season. On the other hand, the floods in Niamey have been particularly frequent in the last decade, a symptom of a change in hydroclimatic behaviour already observed since the end of the great droughts of the 1970s and 1980s and which is identified with the name of Sahelian Paradox. This study, starting from the analysis of the 2020 flood and from the update of the rating curve of the Niamey hydrometric station, analyses the rainfall–runoff relationship on the Sahelian basins of the Medium Niger River Basin (MNRB) that are at the origin of the local flood. The comparative analysis of runoffs, annual maximum flows (AMAX) and runoff coefficients with various rainfall indices calculated on gridded datasets allowed to hydroclimatically characterise the last decade as a different period from the wet one before the drought, the dry one and the post-drought one. Compared to the last one, the current period is characterised by a sustained increase in hydrological indicators (AMAX +27%) consistent with the increase in both the accumulation of precipitation (+11%) and the number (+51%) and magnitude (+54%) of extreme events in the MNRB. Furthermore, a greater concentration of rainfall and extremes (+78%) in August contributes to reinforcing the red flood’s positive anomalies (+2.23 st.dev in 2020). The study indicates that under these conditions the frequency of extreme hydrological events in Niamey will tend to increase further also because of the concurrence of drivers such as river-bed silting and levee effects. Consequently, the study concludes with the need for a comprehensive flood-risk assessment on the Niamey city that considers both recent hydroclimatic trends and urbanisation dynamics in flood zones hence defining the most appropriate risk-reduction strategies.

Performance of the Global Forecast System's Medium-Range Precipitation Forecasts in the Niger River Basin

Weather forecast information has the potential to improve water resources management, energy, and agriculture. This study evaluates the accuracy of medium-range (1–15 day) precipitation forecasts from the Global Forecast System (GFS) over watersheds of eight major dams in the Niger river basin. The Niger basin lies in three latitudinal/climatic sub-regions: Sahel (latitude > 12° N) with annual rainfall of rainfall 400–600 mm, Savannah (latitude 8°–12° N) with annual rainfall of 900–1200 mm, and Guinea Coast (latitude 4°–8° N) with annual rainfall of 1500–2000 mm. The GFS forecast tends to overestimate rainfall in the Guinea Coast and western parts of the Savannah, but estimates well in the Sahel. The overall performance of daily GFS forecast was found to be satisfactory for two watersheds, namely, Kainji (the largest watershed in the basin, predominantly located in the Sahel), and Markala (the second largest watershed, located partly in the Sahel and partly in the Savannah). However, the performance of daily GFS forecast was found to be unsatisfactory in the remaining six watersheds, with GFS forecasts characterized by large random errors, high false alarm, high overestimation bias of low rain rates, and large underestimation bias of heavy rain rates. The GFS forecast accuracy decreases with increasing lead time. The accuracy of GFS forecasts could be improved by applying post-processing techniques involving near-real time satellite rainfall products.