Oleksandra Shumilova, Klement Tockner, Michele Thieme, Anna Koska, Christiane Zarfl

Globally, freshwater is unevenly distributed, both in space and time. Climate change, land use alteration, and increasing human exploitation will further increase the pressure on water as a resource for human welfare and on inland water ecosystems. Water transfer megaprojects (WTMP), i.e. large-scale engineering interventions to divert water within and between catchments, represent an approach in coping with increasing water scarcity. These projects are most commonly associated with large-scale agricultural and energy development schemes, and many of them serve multiple purposes. Despite numerous case studies that focus on the social, economic and environmental impacts of individual projects, a global inventory of existing and planned WTMP is lacking.

We carried out the first comprehensive global inventory of WTMP that are either planned or under construction. We collected key information (e.g. location, distance, volume, costs, purpose) on 33 existing and 76 future (planned or under construction) WTMP. If realized, the future projects will transfer a total volume of 1,923 km3 per year across a total distance exceeding more than twice the length of Earth’s equator. The largest WTMP planned or under construction are located in North America, Asia and Africa. The predicted total investments in these WTMP will exceed 2.6 trillion US$. Among future projects, 43 will serve purposes of agriculture development, 14 transfer water for hydropower development and 10 combine both purposes.

Our results show that WTMP will create artificial connections between river basins, alter the global hydrological cycle, and change the natural functions and services freshwaters provide for humans and nature. The results also emphasize the need to include these projects in global hydrological models, in strategies related to the water-energy-food nexus, and in developing internationally agreed criteria to assess the ecological, social and economic consequences these projects may cause.