RESUMO
STUDY REGION: : The Zambezi River basin, a transboundary basin supplying vital resources to vast human and environmental systems and subject to radical changes linked to climate and infrastructural development. STUDY FOCUS: : Application of a hydrological model (Pitman) established for 76 sub-basins covering the total basin area of about 1 350 000 km2 to assess the potential impacts of increasing water demand under global warming scenarios (1.5, 2, and 3 degree). NEW HYDROLOGICAL INSIGHTS FOR THE REGION: : The application of the calibrated model to the analysis of different combinations of climate change and water use showed that the relative impacts are quite different across the whole Zambezi River basin. The greatest impacts are found in the areas containing large open water bodies (natural and man-made), that are very sensitive to the multiple effects of increased aridity. The uncertainty in the future simulation results remains hugely dependent upon the source of the climate change data and the change signals given by them. The sample RCM data (6 models) used are representative of many more model outputs, while the spread of possible climate change signals remains quite large. However, the main uncertainties do not invalidate the overall message of possible water resources change that is summarized in a substantial decrease in water availability under all the combined scenarios.
RESUMO
STUDY REGION: : The Zambezi River basin, one of the most important water resources in sub-Saharan Africa from both a water supply and hydro-power generation perspective. STUDY FOCUS: : Calibration of two hydrological models (Pitman and WEAP) that have been established for 76 sub-basins covering the total basin area of about 1 350 000 km2. The longer-term purpose of establishing the models is to facilitate scenario analyses of future conditions related to changes in water use and management as well as climate change. NEW HYDROLOGICAL INSIGHTS FOR THE REGION: : While there are many (inevitable) uncertainties in the data used, as well as the models and calibrated parameter sets themselves, the results suggest that the models are generally fit for purpose in terms of evaluating future changes. There are, however, some parts of the basin where the reduction of identified uncertainties would lead to improved models and greater confidence in their future use. One of sources of uncertainty relates to the existence of several large wetland areas that have impacts on downstream flows, but are difficult to simulate due to the relatively poor existing understanding of the dynamics of water exchange between the river channels and the wetland storage areas.
RESUMO
Competition over limited water resources is one of the main concerns for the coming decades. Although water issues alone have not been the sole trigger for warfare in the past, tensions over freshwater management and use represent one of the main concerns in political relations between riparian states and may exacerbate existing tensions, increase regional instability and social unrest. Previous studies made great efforts to understand how international water management problems were addressed by actors in a more cooperative or confrontational way. In this study, we analyze what are the pre-conditions favoring the insurgence of water management issues in shared water bodies, rather than focusing on the way water issues are then managed among actors. We do so by proposing an innovative analysis of past episodes of conflict and cooperation over transboundary water resources (jointly defined as "hydro-political interactions"). On the one hand, we aim at highlighting the factors that are more relevant in determining water interactions across political boundaries. On the other hand, our objective is to map and monitor the evolution of the likelihood of experiencing hydro-political interactions over space and time, under changing socioeconomic and biophysical scenarios, through a spatially explicit data driven index. Historical cross-border water interactions were used as indicators of the magnitude of corresponding water joint-management issues. These were correlated with information about river basin freshwater availability, climate stress, human pressure on water resources, socioeconomic conditions (including institutional development and power imbalances), and topographic characteristics. This analysis allows for identification of the main factors that determine water interactions, such as water availability, population density, power imbalances, and climatic stressors. The proposed model was used to map at high spatial resolution the probability of experiencing hydro-political interactions worldwide. This baseline outline is then compared to four distinct climate and population density projections aimed to estimate trends for hydro-political interactions under future conditions (2050 and 2100), while considering two greenhouse gases emission scenarios (moderate and extreme climate change). The combination of climate and population growth dynamics is expected to impact negatively on the overall hydro-political risk by increasing the likelihood of water interactions in the transboundary river basins, with an average increase ranging between 74.9% (2050 - population and moderate climate change) to 95% (2100 - population and extreme climate change). Future demographic and climatic conditions are expected to exert particular pressure on already water stressed basins such as the Nile, the Ganges/Brahmaputra, the Indus, the Tigris/Euphrates, and the Colorado. The results of this work allow us to identify current and future areas where water issues are more likely to arise, and where cooperation over water should be actively pursued to avoid possible tensions especially under changing environmental conditions. From a policy perspective, the index presented in this study can be used to provide a sound quantitative basis to the assessment of the Sustainable Development Goal 6, Target 6.5 "Water resources management", and in particular to indicator 6.5.2 "Transboundary cooperation".