River management and environmental water allocation in regulated ecosystems of arid and semi-arid regions A review

Rivers make a significant contribution in providing goods and services for human well-being. Today, many rivers and streams have been heavily regulated to ensure adequate provision of water resources for anthropogenic uses. Riverine ecosystems, especially those in arid and semi-arid regions, are experiencing severe stress due to the increasing demands on the ecosystem services they provide, coupled with anthropogenic catchment-scale impacts and factors associated with natural and human-induced climate variability and change. In this paper, the various flow components in regulated riverine ecosystems and the methods to determine environmental flows are reviewed. The review also focuses on the concurrent developments of eco-hydrological models and on the new opportunities for improving environmental flows of rivers by sustainably adjusting consumptive flows to fine-tune environmental flows and maximize the ecological benefit. In fact, the present paper highlights the role of consumptive flows, towards improving environmental flows, which has largely been neglected by river scientists and water managers. Indeed, consumptive flows can provide an opportunity to improve and support environmental flows in regulated riverine ecosystems. Addressing these challenges may aid water management efforts in fmding sustainable solutions in riverine ecosystems by balancing environmental/ecological and human water requirements.