GLOBAL WATER TRANSFER MEGAPROJECTS : 1 A SOLUTION FOR THE WATER-FOOD-ENERGY NEXUS ?

350 words max) 41 Globally, freshwater is unevenly distributed, both in space and time. Climate change, 42 land use alteration, and increasing human exploitation will further increase the pressure on water 43 as a resource for human welfare and on inland water ecosystems. Water transfer megaprojects 44 (WTMP), i.e. large-scale engineering interventions to divert water within and between 45 catchments, represent an approach in coping with increasing water scarcity. These projects are 46 most commonly associated with large-scale agricultural and energy development schemes, and 47 many of them serve multiple purposes. Despite numerous case studies that focus on the social, 48 economic and environmental impacts of individual projects, a global inventory of existing and 49 planned WTMP is lacking. 50 51 We carried out the first comprehensive global inventory of WTMP that are either planned 52 or under construction. We collected key information (e.g. location, distance, volume, costs, 53 purpose) on 33 existing and 76 future (planned or under construction) WTMP. If realized, the 54 future projects will transfer a total volume of 1,923 km 3 per year across a total distance 55 exceeding more than twice the length of Earth’s equator. The largest WTMP planned or under 56 construction are located in North America, Asia and Africa. The predicted total investments in 57 these WTMP will exceed 2.6 trillion US$. Among future projects, 43 will serve purposes of 58 agriculture development, 14 transfer water for hydropower development and 10 combine both 59 purposes. 60 61 Our results show that WTMP will create artificial connections between river basins, alter 62 the global hydrological cycle, and change the natural functions and services freshwaters provide 63 for humans and nature. The results also emphasize the need to include these projects in global 64 hydrological models, in strategies related to the water-energy-food nexus, and in developing 65 internationally agreed criteria to assess the ecological, social and economic consequences these 66 projects may cause. 67 68 69


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Water is an essential resource for human well-being and the functioning of ecosystems. 91 At the same time, increasing water scarcity is among the biggest challenges humanity is facing 92 (WEF, 2015). By 2030, the world will experience a 40% water deficit under a business-as-usual 93 scenario (2030( WRG, 2009). The global distribution of freshwater is uneven both in space and 94 time (Gupta and van der Zaag, 2008), and becomes further exacerbated through changes in total 95 precipitation, seasonality, interannual variability, and the magnitude and frequency of extreme 96 meteorological events (Schewe et al., 2014;Rockström et al., 2014). Water quality is 97 deteriorating, too, due to industrial, agricultural and municipal pollution, further constraining 98 water resources for humans and nature alike (UNESCO-WWAP, 2017).

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While the availability of freshwater remains relatively constant, the demand is growing. 101 This increasing demand is tightly linked to providing food and energy security to growing High water demand increases the risk that water of the required amount and quality will 117 not be available at the time and place it is needed (Gupta and van der Zaag, 2008). This calls for 118 large-scale engineering solutions to store, redistribute and treat water resources. Such 119 megaprojects are often high-risk projects because they require major financial investments, 120 demand long time frames from planning to completion, and may have major socio-economic and 121 environmental ramifications (Flyvbjerg, 2014;Sternberg, 2016). In the water sector, 122 megaprojects include transfer projects, large dams, desalination plants, treatment plants, and 123 ecosystem restoration schemes (Sternberg, 2016;Tockner et al., 2016). Megaprojects are often 124 initiated as an expression of national and political power and expected to trigger economic and 125 social development (Sternberg, 2016). Concurrently, the social, economic and environmental

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Water transfer megaprojects (WTMP) may play an important role in sustaining the water-130 food-energy nexus, as they can provide water for irrigation, domestic supply, energy production, 131 navigation, and industrial development (Sternberg, 2016). In general, water transfer is defined as 132 "the transfer of water from one geographically distinct river basin to another, or from one river 133 reach to another"; hereafter called "donor" and "recipient" system, respectively (Davies et al.,  and key characteristics will help coping with the challenges humans and freshwater ecosystems 167 are facing, and support appropriate strategies for managing water resources and ecosystem 168 processes (Shumilova, 2018).

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The aim of this study was to collate data and information about WTMP that are currently 171 planned or under construction globally, and to be completed by about 2050.

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The key research questions are:

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(1) What is the global distribution of WTMP planned or under construction?

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(2) How much water will be transferred across which distances?

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(3) What are the estimated costs of future WTMP?

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(4) Which purposes will future WTMP fulfill, particularly in meeting the water-food-178 energy nexus?

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In addition, we collected information on the distribution and key characteristics of 181 existing WTMP, in order to put existing and future WTMP into context. Finally, we discuss the 182 consequences WTMP may cause in affecting humans and nature alike.  (Table S1). These criteria were used to identify existing 198 megaprojects, too. 201 We collected data and information on all megaprojects based on peer-reviewed 202 publications, official web-sites of water transfer projects, environmental impact assessments, 203 reports of non-governmental organizations, and information available in online newspapers. Data 204 and information were collected between January and December 2017. We searched for the 205 English terms "water transfer", "water diversion", "water megaproject", and "water 206 redistribution schemes", using various search engines (www.webofscience.com; 207 www.googlescholar.com; www.google.com). In order to improve the data quality, we used 208 multiple sources for each project for cross-validation (the full list of information sources for 209 projects planned and under construction is provided in the Supplementary Material).

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For each project, we compiled the following data and information: geographic location of 212 the project (continent, country), project status (planned, under construction), donor and recipient 213 system, total water transfer distance, total water transfer volume (i.e. maximum annual capacity),   Table S3). The majority of future WTMP will be located in 226 North America (34 projects) and Asia (17) ( Fig. 2

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For existing WTMP, the water transfer volume ranged from 0.06 to 51 km 3 a -1 (median: 231 2.4 km 3 a -1 ), with a combined water transfer volume of 203 km 3 a -1 (Table S2). The "James Bay 232 Project" (Canada; 51 km 3 a -1 ) and the "Goldfields Water Supply Scheme" (Australia; 33 km 3 a -1 ) 233 transfer the largest volumes. For future WTMP, the estimated water volume transferred will 234 range from 0.05 to 317 km 3 a -1 (median: 2.2 km 3 a -1 ), with a combined water transfer volume of 235 1,923 km 3 a -1 (Table 1). The planned "North American Water and Power Alliance" (NAWAPA) 236 megaproject is estimated to transfer 193 km 3 a -1 across the entire continent, and the "Great 237 Recycling and Northern Development (GRAND) Canal of North America" will transfer 317 km 3 238 a -1 .

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The water transfer distance of existing WTMP ranged from 0.4 to 2,820 km (median: 367 240 km) with a combined length of 12,913 km (Table 1). The longest distance of water transfer 241 amounts to 2,820 km for the "Great Manmade River" (Libya) and the California State Water 242 Project (USA; 1,128 km). The calculated water transfer distance of future WTMP will range 243 from 3.2 km to 14,900 km (median: 482 km) ( Table S3). The combined length of all 244 megaprojects planned (51,720 km) or under construction (26,420 km) will amount to 88,140 km. 245 Thereof, the "National River Linking Project" (India), which is under construction, will stretch a 246 total length of 14,900 km, and the planned "NAWAPA" megaproject (North America) will cover 247 10,620 km.

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Among the existing WTMP, twelve projects provide water for irrigation, seven for 266 hydropower generation, four for both purposes, and one project serves ecosystem restoration 267 (Table S2). Among future projects, 43 projects will transfer water for agriculture development, 268 14 for hydropower generation, and ten for both purposes (Fig. 3). Furthermore, six future WTMP 269 will meet the needs of the mining industry, four will support ecosystem restoration, and three 270 projects will serve as navigation canals.   Table S2).

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One of the characteristic of future WTMP revealed by our inventory is that a significant 298 number of projects (15 in total) is transboundary and will transfer water across longer distances 299 compared to existing projects. The median water transfer distance of future WTMP will exceed 300 the values of existing projects by more than 100 km, although the median water transfer volume 301 of existing and future WTMP is very similar (2.4 versus 2.2 km 3 a -1 , respectively). Among the 76 302 future projects, 23 will transfer water further than 1,000 km, compared to two out of 33 existing 303 projects. This highlights the need to consider WTMP as integral parts of the global hydrosystem 304 network, and to consider transferred water volumes in global hydrological models.     Data on expected costs of WTMP show that these projects will require enormous 332 investments, which can be even underestimated. The construction costs of all future WTMP will 333 need more than 2.7 trillion US$, which exceeds the calculated investments for constructing 3,700

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Future WTMP will play a significant role in supporting the water-food-energy nexus. The 371 majority of projects will support the agricultural sector. The Aquatacama Project (Chile), which 372 will transfer around 1.5 km 3 a -1 over a distance of 2,500 km from the South to the North, is

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Within the next decades, we may expect a massive boom in the construction of WTMP.

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As water scarcity becomes a global phenomenon, WTMP are currently considered to be a 442 solution to meet the increasing water demands in both developed and developing countries.

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These projects may play a fundamental role in balancing the water-food-energy nexus, thereby 444 sustaining food production, producing hydropower, and supporting industry. Even projects 445 which seem to be unrealizable and unjustified can become implemented under certain economic 446 and political conditions.

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The lack of solid data does not allow to fully evaluate environmental, social, and 448 economic potential impacts of such projects so far. The size of these WTMP suggests, however, 449 that their impacts will cover regional and continental scales and will be irreversible. Thus, before 450 implementing these risky engineering solutions, the efficiency of water usage needs to be