Evison Kapangaziwiri

Evaluation of recent hydro-climatic changes in four tributaries of the Niger River Basin (West Africa)

ABSTRACT West Africa experienced severe drought during the 1970s and 1980s, posing a threat to water resources. A wetter climate more recently suggests recovery from the drought. The Mann-Kendall trend and Theil-Sen’s slope estimator were applied to detect probable trends in weather elements in four sub-basins of the Niger River Basin between 1970 and 2010. The cross-entropy method was used to detect breakpoints in rainfall and runoff, Spearman’s rank test for correlation between the two, and cross-correlation analysis for possible lags. Results showed an overall increase in rainfall and runoff and a decrease in sunshine duration. Spearman’s coefficients suggest significant (5%) moderate to strong rainfall–runoff correlation for three sub-basins. A significant lower runoff was observed around 1979, with a rainfall break around 1992, indicating possible cessation of the drought. Temperatures increased significantly, at 0.02–0.05°C year-1, with a negative wind speed trend for most stations. Half of the stations exhibited an increase in potential evapotranspiration. EDITOR M.C. Acreman ASSOCIATE EDITOR Not assigned

Assessing the impact of global changes on the surface water resources of Southwestern Nigeria

Abstract Understanding the relative impact of land use, land cover (LULC) and climate change (CC) on basin runoff is necessary in assessing basin water stress, for which long-term observed rainfall time series and LULC spatial data are required. However, there are challenges with the availability of spatio-temporal data, particularly the limited range of available historical hydro-meteorological measurements. The study used long-term (1961–2007) rainfall data to drive the Pitman monthly rainfall–runoff model to assess changes to the water resources of three basins in Nigeria—Asa, Ogun and Owena. Three CGCMs—CSIRO Mark3.5, MIROC3.2-medres and UKMO-HadCM3—dynamically downscaled to a 60 km by 60 km grid using the Conformal-Cubic Atmospheric Model (C-CAM) are used to simulate impacts of future climate changes on water resources. These three models were found suitable for simulating rainfall–runoff based on the insignificant differences of the modelled mean with mean of observed rainfall and temperature for pre-2010 data compared to other downscaled C-CAM models (GFDL-CM2.0, GFDL-CM2.1 and ECHAM5/MPI-Ocean model). The model results show increases in the runoff coefficient with decreases in forest cover between 1981 and 2007, with average runoff coefficients of 5.3%, 12.0% and 6.4% for Asa, Ogun and Owena basins respectively. Based on annual reduction in rainfall trend projected by CSIRO, MIROC and UKMO, the future scenarios revealed a low runoff coefficient for the three basins—Asa (CSIRO 6.0%, MIROC 6.0% and UKMO 5.9%), Ogun (CSIRO14.6%, MIROC 14.6% and UKMO 14.4%) and Owena (CSIRO 8.5%, MIROC 8.7% and UKMO 8.9%). In all scenarios, Asa basin has a lower runoff coefficient when compared to Ogun and Owena basins, indicating that future water stress in Asa basin would be much greater. Editor Z.W. Kundzewicz; Guest editor D. Hughes

Modelling blue and green water availability under climate change in the Beninese Basin of the Niger River Basin, West Africa

Copyright: 2018 Wiley. Due to copyright restrictions, the attached PDF file contains the preprint version of the published item. For access to the published version, please consult the publishers website.