The call for measuring synergies and trade-offs between water, energy, and food is increasing worldwide. This article presents the development and application of a country-level index that has been calculated for 181 nations using open databases. Following an assessment of 87 water-, energy-, and food-related indicators, 21 were selected to constitute the Water-Energy-Food (WEF) Nexus Index. In this article, the WEF Nexus Index is utilized to assess the Southern African Development Community, where it demonstrates that food security is an area of concern, while the potential for beneficially exploiting water resources and energy projects exists in several countries. Water for agriculture could be achieved through the drought-proofing of rainfed agriculture and systematic irrigation development, with energy as the critical enabler. Neither the composite indicator nor the WEF nexus approach is the panacea that will solve all the significant development or environmental challenges facing humanity. However, they could contribute to integrated resource management and policy-making and are complementary to the Sustainable Development Goals. In this study, the methodology set out by the Joint Research Centre's Competence Center on Composite Indicators and Scoreboards has been followed. A set of visualizations associated with the WEF Nexus Index have been compiled in an interactive website, namely www.wefnexusindex.org.
Human activities both aggravate and alleviate streamflow drought. Here we show that aggravation is dominant in contrasting cases around the world analysed with a consistent methodology. Our 28 cases included different combinations of human-water interactions. We found that water abstraction aggravated all drought characteristics, with increases of 20 to 305% in total time in drought found across the case studies, and increases in total deficit of up to almost 3000%. Water transfers reduced drought time and deficit by up to 97%. In cases with both abstraction and water transfers into the catchment or augmenting streamflow from groundwater, the water inputs could not compensate for the aggravation of droughts due to abstraction and only shift the effects in space or time. Reservoir releases for downstream water use alleviated droughts in the dry season, but also led to deficits in the wet season by changing flow seasonality. This led to minor changes in average drought duration (-26 to +38%) and moderate changes in average drought deficit (-86 to +369%). Land use showed a smaller impact on streamflow drought, also with both increases and decreases observed (-48 to +98%). Sewage return flows and pipe leakage possibly counteracted the effects of increased imperviousness in urban areas; however, untangling the effects of land use change on streamflow drought is challenging. This synthesis of diverse global cases highlights the complexity of the human influence on streamflow drought and the added value of empirical comparative studies. Results indicate both intended and unintended consequences of water management and infrastructure on downstream society and ecosystems.
The hydrological responses of a catchment are sensitive to, and strongly coupled to, land use and climate, and changes thereof. The hydrological responses to the impacts of changing land use and climate will be the result of complex interactions, where the change in one may moderate or exacerbate the effects of the other. A further difficulty in assessing these interactions will be that dominant drivers of the hydrological system may vary at different spatial and temporal scales.
To assess these interactions, a process-based hydrological model, sensitive to land use and climate, and changes thereof needs to be used. For this purpose the daily time step ACRU model was selected. However, to be able to use a hydrological model such as ACRU with confidence its representation of reality must be confirmed by comparing simulated output against observations across a range of climatic conditions. Comparison of simulated against observed streamflow was undertaken in three climatically diverse South African catchments, ranging from the semi-arid sub-tropical Luvuvhu catchment, to the winter rainfall Upper Breede catchment and the sub-humid Mgeni catchment. Not only do the climates of the catchments differ, but their primary land uses also vary. In the upper areas of the Mgeni catchment commercial plantation forestry is dominant, while in the middle reaches there are significant areas of commercial plantation sugarcane and urban areas, while the lower reaches are dominated by urban areas. The Luvuvhu catchment has a large proportion of subsistence agriculture and informal residential areas. In the Upper Breede catchment in the Western Cape, commercial orchards and vineyards are the primary land uses.
Overall the ACRU model was able to represent the high, low and total flows, with satisfactory Nash-Sutcliffe efficiency indexes obtained for the selected catchments. The study concluded that the ACRU model could be used with confidence to simulate the streamflows of the three selected catchments and was able to represent the hydrological responses from the range of climates and diversity of land uses present within the catchments
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