Perceptions of environmental flows by the riparian communities to assess the role of reservoir ecosystem services in the Himalayan river Tista, India

Abstract:

The constructions and operations of reservoirs across the globe have altered the environmental flows (E-Flows) of the river. However, reservoirs play an important role to provide essential ecosystem services (ES) to the surroundings. While, riparian communities are considered as an integral part of the river ecosystem. Thus, riparian communities can better perceive the impact of reservoirs to maintain the E-Flows and further alteration of ES on the Himalayan river Tista which also shares the E-flows across the border between India and Bangladesh. The study combined the qualitative and quantitative data to prepare a framework for the evaluation of positive and negative impacts of reservoirs on E-Flows. Qualitative data documented the perceptions of the communities across different physiographic locations (hill, foothill and plain) of the basin through Focused Group Discussions (FGDs) and quantitative data analyzed the hydrologic and satellite data. The assessment of E-Flows and ES are primarily based on four major indicators: hydrological, ecological, economic and political. These indicators are further divided into fourteen broad categories and twelve sub-categories of benefits and challenges. The analysis found that the communities in the hills are more sensitive to climate change, ecological alteration and shrinking water sources due to reservoir operations. Similarly, communities in the foothills are sensitive to sedimentation and reservoir water-level variations affecting the ES. Whereas, communities on the downstream plains are vulnerable to seasonal flow regulation, sedimentation, flooding and erosion. Hence, the perceptions among communities varied spatially due to differential access to reservoir ES which is principally determined by the E-Flows condition in different physiographic locations of the basin. Again, the riparian communities across the border are largely dependent upon the optimum streamflow (E-Flows) for life and livelihoods. As a result, the historic demand of 50-50 equal proportion of Tista water by downstream Bangladesh has provoked the geopolitics of transboundary water-sharing. Thus, integration of community perceptions on E-Flows to evaluate the reservoir ES are very crucial for future water-sharing and for sustainable river water management across the border.