Abstract. Floods are devastating natural disasters with a significant impact on human life and the surrounding environment. This paper analyses historical and recent flood (2012 extreme) peak flow at strategic locations, land use activities and Floodplain Vulnerability Index analyses of the Niger-Benue River Floodplain. The 2012 peak flow at Jederbode on the Niger River was about 50 % above the long term average. At Jebba (Niger), the 2012 peak flow of 1567 m 3 s −1 was also far higher than the long term mean annual peak flow of 1159 m 3 s −1 . The 2012 peak flow at Lokoja was also about 50 % above the historical average. The Benue River at Makurdi had peak flow of 16 387 m 3 s −1 which was also unusually higher than the historical average while Wuroboki (Benue) had peak flow of 3362 m 3 s −1 which was also much higher that the historical average (694 m 3 s −1 ). The mixed land use which supported diverse ecosystem services has the largest cover of 5654 km 2 (36.85 %) of the Niger-Benue floodplain. The flood vulnerability of the various land uses within the floodplain include; medium, high and very high levels. A four levels hierarchical implementation adaptation strategy for sustainable agricultural practices along the rivers flood plain was proposed. The implementation hierarchy includes: Community Concern, Local Authority Concern, State Concern and National Concern.
Understanding the role of ecosystem services (ESs) within environmental management has become a critical issue of the twenty-first century. This is because scientific study of ES interactions can aid effective planning and management of ESs, thus curtailing degradation and enhancing restoration. In this study, ES interactions of the climate-sensitive West African Sokoto-Rima basin were quantified using land cover and a series of GIS-derived data as inputs into the InVEST model. Crop production (CP), seasonal water yield (SWY), habitat quality (HQ), and nutrient retention ratio (NRR) between 1992 and 2015 were assessed. Climate change assessment was based Mann-Kendall trend of precipitation and temperature for both past and future climates. The climate dynamics present a drying-warming trend with localised cooling-warming spells in some locations and a general future wetting-warming trend. Areas dominated by cropland and CP exert significant influence on the spatiotemporal dynamics of ES interactions contributing to the manifestation of substantial trade-offs and synergies across the past ( 2015) and the future ( 2050) climates. This also regulates the overbearing pattern of multiple ES interactions such that the relationship CP > SWY > HQ > EVI > NRR was observed over the study area. The persistence of these diverse relationships will stimulate the possible degradation of natural regulating ESs. Improvement of existing crop cultivation clusters, cultivation of flood-resistant crop varieties, and agroforestry expansion were proposed as climate and ESs interaction-based restoration measures. When adopted, these measures will douse the increasing ES pressures within this semi-arid zone. KeywordsEcosystem service interactions • InVEST model • Climate change • Ecological restoration • Sokoto-Rima basin * Saheed A. Raji
The Sokoto-Rima basin defines the natural and socioeconomic lifeblood of northwestern Nigeria. Its agrarian nature is an indication of significant dependence on the supply of ecosystem services from its various rivers, streams, and wetlands. However, nitrogen (N) and phosphorus (P) constitute a great portion of chemical fertilizers used to enhance crop yields and poor management of these portend great threats for water quality. The overarching objective of this study was to examine the extent of spatial variation of nutrient dynamics in the Sokoto-Rima basin between 1992 and 2015 using the nutrient delivery ratio (NDR) model of InVEST (Integrated Valuation of Ecosystem Service and Tradeoffs) software. Land use/landcover, precipitation, digital elevation, and biophysical variables were the principal datasets employed as model input. The result of the study showed that the surficial N load is almost 15-fold of P in the Sokoto-Rima basin. Over the period of study, cultivated areas and rivers were spatially detected as nutrient sources and sinks respectively. The subsurface nutrient load is dominated by P while the amount of N load is insignificant. The trend of nutrient export is linearly defined: with 0.87% and 1.7% increase in N and P export respectively during 1992-2015. N and P exports vary spatially with a north-south increase-decrease index. Critical length and threshold are highly sensitive to changes in the parameterization of the NDR model. Thus, synergistic cultivation practices such as agroforestry should be extended to existing crop cultivation complexes to curtail nutrient enrichment in the Sokoto-Rima basin and ensure environmental sustainability.
Land degradation is one of the most ubiquitous environmental challenges affecting the semi-arid ecosystems of the world and the Sokoto-Rima basin is not immune to this. In this study, we evaluated vulnerability of the Sokoto-Rima basin to land degradation by combining remote sensing and geographic information system technologies. An appraisal model was developed for the identified nine variables, whose weights were ascertained by the analytical hierarchy process. Using this model, we examined the spatiotemporal distribution of vulnerability to land degradation stimulated by climate change from 2002 to 2015. Largely, the basin is extremely vulnerable to land degradation with roughly 88% of the land area in 2002, 2012 and 2015 while areas with low vulnerability were just 1.52%, 1.48% and 1.51% respectively. Geographically, there exists a north-south vulnerability index dichotomy as the index increases northwards. Also, integrated vulnerability index showed that the entire basin is getting exposed to the vagaries of climate change that stimulates land degradation. Large-scale resilience projects such as greening and integrated shelter-belts and woodlots can be implemented in the long run as existing ones are inadequate to address the observed degradation.
One of the most pressing environmental issues of the 21st century is land degradation in fragile watersheds where acute sediment aggradation, erosion, and flooding have become everyday occurrences. Previous attempts to prioritise sub-watersheds have been plagued with uncertainty. Addressing this problem therefore requires identifying erosion-prone areas, specifically at the sub-watersheds level, and reducing the uncertainty of outcomes to a minimum. In this study, an ensemble of seven multi-criteria decision-making (MCDM) models was developed to prioritise the sub-watersheds of the Anambra Basin against erosion risk. These MCDM models, namely MOORA (multi-objective optimisation based on ratio analysis), GRA (grey relational analysis), CoCoSo (combined compromise solution), CODAS (combinative distance-based assessment), TOPSIS (a technique for order preference by similarity to ideal solution), COPRAS (complex proportional assessment), and VIKOR (VieKriterijumsko KOmpromisno Rangiranje), were coupled with the Analytical Hierarchical Process (AHP) and Geographic Information System (GIS) with 23 geomorphometric parameters to provide an integrated sub-watershed ranking. The accuracy of the models was tested using Spearman's rank correlation and geometric mean to compute a uniform sub-watershed ranking. The results indicate that sub-watershed H has the highest aggregate ranking across the MCDM models, making it the top priority for erosion mitigation projects. Furthermore, the model validation assessment shows that the MOORA and COPRAS models returned similar results with the aggregated ranks and possess the most significant rank correlation coefficients, indicating the highest predictive accuracy. This study can be utilised by decision-makers in data-sparse regions for sustainable watershed management in the face of erosion risks.
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