Abstract
The sustainability of social-ecological systems depends on river flows being maintained within a range to which those systems are adapted. In order to determine the extent of this natural range of variation, we assess ecological flow thresholds and the occurrence of potentially damaging flood events to society in the context of the Lower Brahmaputra river basin. The ecological flow threshold was calculated using twenty-two ‘Range of Variability (RVA)’ parameters, considering the range between ± 1 standard deviation from the mean of the natural flow. Damaging flood events were calculated using flood frequency analysis of Annual Maxima series and using the flood classification of Bangladesh. The climate change impacts on future river flow were calculated by using a weighted ensemble analysis of twelve global circulation models (GCMs) outputs driving a large-scale hydrologic model. The simulated climate change induced altered flow regime of the Lower Brahmaputra River Basin was then investigated and compared with the calculated threshold flows. The results demonstrate that various parameters including the monthly mean of low flow (January, February and March) and high flow (June, July and August) periods, the 7-day average minimum flow, and the yearly maximum flow will exceed the threshold conditions by 1956–1995 under the business-as-usual A1B and A2 future scenarios. The results have a number of policy level implications for government agencies of the Lower Brahmaputra River Basin, specifically for Bangladesh. The calculated thresholds may be used as a good basis for negotiations with other riparian countries of the basin. The methodological approach presented in this study can be applied to other river basins and provide a useful basis for transboundary water resources management.
Highlights
Freshwater systems are part of larger ecosystems which sustain life and all social and economic processes
The specific objective of this study is to propose a generalized framework for scientifically based vulnerability assessment to support participatory decision making processes in the field of water resources management (WRM), with a specific interest for climate change adaptation (CCA)
The concepts of vulnerability assessment for water resources systems was reviewed, with the aim of facilitating the work of those who are active in the field of water management in developing countries by moving towards operational solutions
Summary
Freshwater systems are part of larger ecosystems which sustain life and all social and economic processes. Scientists within the Intergovernmental Panel on Climate Change (IPCC) expect that the present increase in greenhouse gas concentrations will have direct first-order effects on the global hydrological cycle, with impacts on water availability and demand [3]. Overall at the global level, a net negative impact on water availability and on the health of freshwater ecosystems is foreseen [5], and a cascade of negative consequences is expected to affect social and ecological systems and their processes
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