Water quantity as a driver of change in the Great Lakes–St. Lawrence River Basin

Journal of Great Lakes Research 41 Supplement 1 (2015) 84–95

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Water quantity as a driver of change in the Great Lakes–St. Lawrence River Basin☆ Mahdi Maghrebi a,1, Deasy Nalley b,⁎, Katrina L. Laurent c,2, Joseph F. Atkinson a,3 a b c

Department of Civil, Structural, and Environmental Engineering, University at Buffalo, Buffalo, NY 14260, USA Department of Bioresource Engineering, McGill University, Ste-Anne-de-Bellevue, Quebec H9X 3V9, Canada Department of Biology, Western University, 1151 Richmond St. London, Ontario N6A3K7, Canada

a r t i c l e

i n f o

Article history: Received 27 October 2013 Accepted 12 November 2014 Available online 15 January 2015 Communicated by Irena Creed Keywords: Water quantity Water levels Anthropogenic activities Natural factors Future scenarios

a b s t r a c t This article aims to evaluate and illustrate the state of water quantity in the Great Lakes–St. Lawrence River basin in the past, present, and future. Historical water levels in the Great Lakes basin since 1963 are presented and the interrelationships among the main factors regulating water levels are explored. These factors include both natural processes (over-lake precipitation, lake evaporation, and land surface runoff) and anthropogenic activities (consumptive water use, lake level regulations, and water diversions). The impacts of each of these factors on the historical levels, as well as their influences on future trends are assessed. Linear data trends from 1963 to 2013 were found to adequately represent past data and indicate that overall the basin is in a state of increasing precipitation, runoff and evaporation. Informed by these trends, and also taking into consideration other impacts on water levels within the Great Lakes basin, three future scenarios are presented describing projections to the year 2063 — status quo, dystopia (water scarcity), and utopia (water surplus). These future scenarios consider both the natural and anthropogenic controls impacting water levels in the Great Lakes basin, while also considering the relationships among variable water levels and other defining characteristics of the system and providing a creative means to project alternate water realities into 2063. © 2014 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.

Introduction: water quantity in the Great Lakes The Great Lakes–St. Lawrence River basin, consisting of Lakes Superior, Michigan, Huron, Erie and Ontario, is the largest surface freshwater system in the world (Fuller and Shear, 1995). The basin spans eight states in the US and two provinces in Canada (Manninen and Gauthier, 1999) and makes up the largest coastline (approximately 4500 miles long) within the US when compared with the country's Atlantic, Pacific or Gulf of Mexico coasts (NOAA, 1975). The waters of the Great Lakes basin have played an important role in shaping the US and Canada (Fuller and Shear, 1995) and they continue to play this important role for the basin's approximately 45 million residents who rely on them for a multitude of uses (Camp Dresser McKee, 2010). These uses include public water supplies, domestic use, industry, navigation, tourism and recreation, power generation, and agriculture ☆ The Great Lakes Futures Project brought together graduate students and expert mentors from universities and institutions in Canada and the United States. Each paper required collaboration between a number of authors with many of them sharing co-leadership that we denote using a †. ⁎ Corresponding author. Tel.: +1 5142240492. E-mail addresses: [email protected] (M. Maghrebi), [email protected] (D. Nalley), [email protected], [email protected] (K.L. Laurent), [email protected] (J.F. Atkinson). 1 Tel.: +1 7166454004. 2 Tel.: +1 519 661 2111x86843. 3 Tel.: +1 7166452088.

(Shaffer and Runkle, 2007). In addition to the human population, these waters also play an important role ecologically, sustaining the world's largest system of freshwater dunes, endemic coastal plants and animals, and deep-water fish (Pearsall et al., 2013). It is therefore no surprise that changes in the quantity of water within the basin has, does, and will continue to have significant impacts on the population and ecosystems that rely upon them. The water levels within the Great Lakes basin are influenced mainly by fluctuations acting on three different time scales: short term (several hours to several days); seasonal (changes between seasons over the year); and long term (over multiple years) (Manninen and Gauthier, 1999). These fluctuations are influenced by both natural and anthropogenic factors such as precipitation, upstream inflows, surface water runoff, evaporation, diversions, and water level regulation (Cengiz, 2011), as well as the rebounding of the Earth's crust, known as glacial isostatic adjustment (Mainville and Craymer, 2005). Although it is possible to consider water levels directly to analyze longer-term trends in water supply, it is more useful to include analyses of important hydrological drivers that control water levels. These drivers are used in calculating the hydrologic water balance in the basin, or an individual lake, by subtracting outputs (evaporation, outflow into connecting channels, and man-made diversions into or out of a lake) from inputs (precipitation on the lake, runoff into the lake, and connecting channel inflow) (Assel et al., 2004). The difference between outputs and inputs is reflected in the changes in storage. However, in the Great Lakes basin,

http://dx.doi.org/10.1016/j.jglr.2014.12.005 0380-1330/© 2014 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.

M. Maghrebi et al. / Journal of Great Lakes Research 41 Supplement 1 (2015) 84–95

the three main factors of the water volume budget overall (as reflected by water levels) have been identified as over-lake precipitation, lake evaporation and land surface runoff (Gronewold et al., 2013; Gronewold and Stow, 2014; Manninen and Gauthier, 1999). Therefore these three main factors, in addition to the discussion of water levels themselves, are the main focus of this paper, with primary interest on longer-term trends (i.e. years to decades). This study explores these key factors and considers possible trend projections into the future. As one paper of a collective group making up a 100-year scenario analysis that was the focus of the Great Lakes Futures Project (GLFP; Creed and Laurent, 2015), this report explores how water levels and components of the water volume budget of the basin have changed in the 50 years prior to 2013, and explores three alternative future scenarios set in the year 2063. These three scenarios are status quo, dystopia (relative water scarcity), and utopia (relative water abundance). This study explores the intricate interactions of water quantity with other important drivers of change identified in the GLFP (Laurent et al., 2015) such as the economy, energy, governance, and demographics. In the following sections, we review information available to characterize key factors controlling water levels in the past 50 years, discuss influences of other factors included in the GLFP on water levels, look at how past conditions and trends may be used for future projections, and describe conditions for each of the three future scenarios.

A look back: water levels and water volume balance in the Great Lakes basin since 1963 The Great Lakes basin has a rich history of water level measurements dating back to the 1800s with measurements taken by the US Lake Survey District of the Army Corps of Engineers and to the 1900s in Canada with measurements taken by the Department of Public Works (Gronewold et al., 2013). This history of water level measurement has facilitated a rich historical synthesis of how these water levels have changed over time (Croley et al., 1996; Gronewold, et al., 2013; Manninen and Gauthier, 1999). Each of the Great Lakes undergoes water level changes, with low water levels occurring in the winter, followed by snow melt and spring precipitation causing water levels to rise and reach an early summer maximum, only to decline again when the net water supplies diminish over late summer and fall (Croley et al., 1996). When considered over longer periods of time, for example from 1963 to 2011, fluctuations in water levels of up to 0.5 m annually have been observed. The lowest water level fluctuations have occurred in Lake Superior, followed by Michigan–Huron (considered one hydrological unit due to their connection through the deep Straits of Mackinac) (Croley et al., 1996), Erie, and Ontario (Table 1). Furthermore, when the average annual water levels relative to the International Great Lakes Datum 1985 (IUGLS, 2012) reference elevation are plotted against time for the Great Lakes basin from 1900 to 2011, it is evident that each of the Great Lakes' water levels responds differently over time (Fig. 1), in

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response to the relative effects of different natural and human controls in each of the lakes. For example, Lake Ontario water levels are strongly affected by flow controls at the hydroelectric facility at Cornwall, and do not exhibit the same responses to variations in natural processes as is seen in the other lakes. However, similarities can also be seen among the lakes, with Lake Erie and Lake Michigan–Huron showing similar trends (Fig. 1). It should be noted that extreme fluctuations have occurred in the basin, with record lows occurring in 1964 (Croley et al., 1996; Bates et al., 2008) and from 1997 to 1998 (Gronewold and Stow, 2014), and record highs from 1973 to 1986 (Croley et al., 1996). A water volume budget for each lake can be developed by considering inputs, and outputs and changes in storage (Assel et al., 2004). The contribution of each of these components is different for each lake in the basin (Table 2). Over-lake precipitation, lake evaporation and land surface runoff are the dominant factors that have influenced net water supplies in Lakes Superior and Michigan–Huron from 1948 to 2006 (IUGLS, 2009; Table 2), making their water levels more variable in periods of prolonged drought or high frequency precipitation. For Lakes Erie and Ontario, the dominant factors are inflows and outflows (IUGLS, 2009; Table 2). Over-lake precipitation Most episodic changes in water levels of the past century may be attributed to corresponding changes to basin-wide over-lake precipitation (Assel et al., 2004). For example, Gronewold et al. (2013) showed that the historical variability detected in annual basin-wide precipitation over the last 100 years coincides with annual water level fluctuations, and Assel et al. (2004) linked trends in precipitation over the basin to the historical water level increases across the Great Lakes basin in the late 1960s, early 1970s, and early 1980s, and also to the water level decreases seen in the basin in the late 1980s. The link between over-lake precipitation and water levels in the lakes is not always clear. For instance, in Lakes Michigan–Huron, Erie, and Ontario, the drop in water levels between 1997 and 2000 occurred irrespective of the relatively stable annual precipitation (Gronewold et al., 2013). Assel et al. (2004) attributed this result to elevated temperatures for Lake Michigan–Huron. For a synthesis of precipitation changes in response to changing climate within the basin since 1963 in the context of the GLFP, refer to Bartolai et al. (2015). Lake evaporation Evaporation depends on several physical variables including surface temperature, air temperature, humidity, wind speed, and ice cover (Croley et al., 1996). Historical changes in Great Lakes water levels over the past 50 years, such as the water level drops that occurred in the late 1990s, have been shown to coincide with significant increases in Great Lakes surface water temperatures as seen in Lake Michigan– Huron (Assel et al., 2004), and lake evaporation rates (Gronewold et al., 2013). Historical variation in evaporative loss can be seen on an annual basis, with the main loss of water (more than half the annual total evaporation) occurring between August and January for each of

Table 1 Water level statistics of the Great Lakes basin during the period of 1963–2011 in meters (feet in parenthesis) (GLERL, 2012). Lake

Superior Michigan–Huron Erie Ontario Average

Annual water level fluctuations in meters (ft)

Water level in meters (ft) Min.

Average

Max.

Min.

Average

Max.

183.0 (600.4) 175.7 (576.4) 173.6 (569.6) 74.3 (243.8)

183.4 (601.7) 176.5 (579.1) 174.3 (571.9) 74.8 (245.4)

183.7 (602.7) 177.3 (581.7) 174.9 (573.8) 75.2 (246.7)

0.2 (0.66) 0.2 (0.66) 0.3 (0.99) 0.4 (1.31)

0.3 (0.99) 0.4 (1.31) 0.5 (1.64) 0.7 (2.3) 0.475

0.7 (2.3) 0.6 (1.97) 0.8 (2.62) 1.1 (3.61)

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Fig. 1. Time series of average annual water level in the Great Lakes basin during the period 1960–2011. The horizontal line shows the average water level in this period. The dashed black line shows chart datum for the lake (GLERL, 2012).

the lakes, a period that typically precedes the onset of significant ice cover (Clites et al., 2014). It is generally thought that evaporation from lake surfaces is highest during the winter months under ice-free conditions when relatively cool dry air passes over the warmer waters of the lakes (IUGLS, 2009), and historically, peaks have been observed in October to November on Lake Erie and in November to December on Lake Superior (Croley et al., 1996). Analysis has shown that declining ice cover is negatively correlated with lake evaporation for the months of January, February, and March for both Lakes Erie and Huron, and overall, ice cover is positively related to elevated lake levels (IUGLS, 2009). Land surface runoff Land surface runoff is the amount of precipitation on the land (the watershed) that does not evaporate into the atmosphere but drains through a variety of paths into stream channels (Mortsch et al., 2000) and eventually into receiving water bodies such as the Great Lakes. In order to assess runoff in the Great Lakes basin, different models have been established, such as that of Croley and Hunter (1994). Runoff within the basin is seasonally variable, with a spring peak due primarily to

spring snow melt, followed by a minimum during the summer and early fall due to elevated evapotranspiration from the land basin (Croley et al., 1996). Furthermore, high levels of runoff may occur for months following elevated precipitation events in the basin, because of the buffering of the basin's large snowpack and large soil, groundwater, and surface storage systems (Croley et al., 1996). Analyzing data from 1951 through 1988, Croley et al. (1996) found that annual runoff rates differed among each of the lakes, where Lake Ontario showed the highest value at 169 cm/year and Lake Superior showed the lowest at 62 cm/year. These variations in runoff within the basin may be accounted for by changes in climate, with reductions most severe when temperature increases and precipitation decreases (Mortsch and Quinn, 1996). Long-term oscillations impacting precipitation, evaporation and runoff The fluctuations and variability in water levels in the Great Lakes basin are also influenced by the variability of several dominant global atmospheric circulation patterns. Examples include the El Niño Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), North Atlantic

Table 2 Components of water supply into/out of the Great Lakes basin in percent as well as actual values in m3/s (thousand ft3/s in parenthesis) for the period 1948–2006 (IUGLS, 2009). Lake

Supply

Losses

Inflow

Precipitation

Runoff

Diversions

Outflow

Evaporation

Diversions

Superior

– 27% 2110 (75) 79% 5360 (189) 79% 5780 (204)

40% 1460 (52) 34% 2670 (94) 10% 660 (3) 15% 1160 (41)

4% 160 (6) –

57% 2110 (75) 68% 5360 (189) 89% 5780 (204) 93% 7060 (249)

43% 1560 (55) 31% 2450 (87) 11% 750 (6) 7% 530 (19)

–

Michigan–Huron

56% 2050 (72) 39% 3120 (110) 11% 750 (6) 6% 410 (14)

Erie Ontario

– 9500*

1% 90 (3) 9500* –

(*) “The Welland and NY State Barge canals are intra-basin diversions, which means that the diverted water does not leave the Great Lakes basin; they are not considered as part of the overall water budget for the lakes, although they do contribute to the individual budgets for Lakes Erie and Ontario” (IUGLS, 2009).

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Fig. 2. Great Lakes basin and its jurisdictions. Main connecting channels and water diversions are also indicated.

Oscillation (NAO), and Atlantic Multidecadal Oscillation (AMO), among others. These atmospheric circulations affect the Great Lakes levels through over-lake precipitation, lake evaporation, and air temperature (Ghanbari and Bravo, 2008). Several recent studies have analyzed the nature of the influence of these atmospheric circulations on the water levels and other hydroclimatic variables in the Great Lakes basin over different time scales (e.g. Cengiz, 2011; Ehsanzadeh et al., 2013; Ghanbari and Bravo, 2008; Liu, 2000; Mengistu et al., 2013; Rodionov, 1994). These studies have demonstrated that the influence of atmospheric circulations on the variability of lake levels in the Great Lakes basin area occur at different time scales. For example, for data between 1918 and 2002, the levels in all of the Great Lakes are significantly correlated with the ENSO index at the inter-annual time scales of 3–7 year wavebands. In addition, Pacific North American (PNA) and PDO are correlated with lake levels at the inter-decadal scales of 13 and 14 years, respectively (Ghanbari and Bravo, 2008). Cengiz (2011) found that water level periodicities are seen mainly for the 12-month or annual cycle for Lakes Superior, Erie, and Ontario. In contrast, Lake Michigan showed generally long-term periodicities in water levels of more than 10 years, which was due to the stronger influences of inter-annual atmospheric variability (e.g. ENSO, NAO, and global warming) than the other three lakes (Cengiz, 2011). The NAO and PDO indices are also correlated with water yields at the inter-annual scales, where water yield is defined in terms of precipitation and water storage in wetlands in a catchment. The AMO is significant in affecting temperature and precipitation in the northern part of the Great Lakes basin — higher ENSO or higher AMO values result in lower water yields (Mengistu et al., 2013). Consistent positive correlations between AMO and temperature have been observed, which may indicate that increases in atmospheric temperature are due not only to anthropogenic factors but also to

natural oscillations, and negative correlations between AMO and precipitation were observed from 1964 to 2010 (Mengistu et al., 2013). Drivers of change that impact water quantity in the Great Lakes–St. Lawrence River basin In this section we examine how the drivers of change identified for the GLFP, including climate change, biological and chemical contaminants, invasive species, governance and geopolitics, societal values, demographics, the economy and energy (Laurent et al., 2015) interact with water levels in the Great Lakes basin. The impacts of both consumptive and non-consumptive water uses are explored, along with how they relate to the drivers of change for the GLFP. Climate change The impacts of climate change are intimately linked to the forces driving water levels in the Great Lakes basin. For instance, increases in air temperature can have many impacts on the basin's hydrological cycle such as by decreasing runoff to the lakes through an enhancing effect on transpiration and water loss (Croley et al., 1996). Furthermore, increased air temperatures can lead to increases in lake evaporation water loss (Croley et al., 1996) and to increases in the rate of ice cover melting, which also cause decreases in water levels (due to increased time for evaporative loss), similar to those seen in the basin in the late 1990s (Gronewold and Stow, 2014). Surface water temperature also impacts wind speed over the lakes (Austin and Colman, 2007), which enhances evaporation (Manninen and Gauthier, 1999). The potential impacts of climate variations, temperature, and ice cover changes on the basin's water levels can be seen by the impacts of the 1997–1998 El Niño event. This event, characterized by a surface water temperature increase of ~ 2.5 °C from 1997 to 1998 on Lakes

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Table 3 Major existing water diversions occurring in the Great Lakes basin (IJC, 2000). Name

Type

Associated Lake

Initial operation year

Average annual flow in m3/s (ft3/s)

Long Lac Ogoki Chicago NY State Barge Canal Welland Canal

Interbasin (inflow) Interbasin (inflow) Interbasin (outflow) Intra-basin Intra-basin

Lake Superior Lake Superior Lake Michigan Lake Erie to Lake Ontario Lake Erie to Lake Ontario

1941 1943 1848 1825 1829

45 (1590) 113 (3990) 91 (3200) 28 (700) 260 (9200)

Ontario and the St. Lawrence River have occurred since the plan was implemented. The newly released plan, Plan 2014, aims to protect all water use interests from the effects of extreme water levels, to restore the damage that has been done to wetlands and shorelines, and to prepare for a changing Great Lakes future (IJC, 2014). Water diversions into and out of the Great Lakes basin have played, and continue to play, an important role in regulating Great Lakes water levels, and they are a contentious subject from a governance and geopolitical perspective. The major water diversion operations within the basin include Ogoki and Long Lac, Lake Michigan at Chicago, and the New York Barge Canal (Fig. 2; Table 3; USACE and GLC, 2009). The Ogoki and Long Lac diversions, which divert water into Lake Superior from the Hudson Bay watershed in northern Ontario, are a current source of hydropower (USACE and GLC, 2009) and account for 4% of the water supply into Lake Superior (IJC, 2000). The Lake Michigan diversion at Chicago, which diverts water out of Lake Michigan, provides a source of water that is mainly used for domestic and sanitation purposes as well as to support commercial navigation in the Chicago River (USACE and GLC, 2009). The oldest, smallest, and least impactful diversion within the basin occurs at the New York Barge Canal, which diverts water from the Niagara River and connects Lake Ontario with the Hudson River (USACE and GLC, 2009). It is also worth noting that even though the Welland Canal, which connects Lakes Erie and Ontario, is considered a diversion, it is an intra-basin diversion and does not affect the overall net water quantity for the entire basin. Net flows are assumed to be negligible for the water balances for each of these lakes. Currently, there is more water being diverted into rather than out of the Great Lakes basin, as seen from data modified from Cuthbert and Moulton (1999) by Barko et al. (1999). Since the operation of the Ogoki and Long Lac inflow diversions commenced in 1941 and 1943, respectively, the cumulative change in the water level of Lake Superior has been an increase of 3 cm (Barko et al., 1999). This increase is balanced by the Chicago outflow to produce net zero changes in water levels for Lakes Michigan–Huron. Lakes Erie and Ontario have experienced a cumulative decrease in water levels of 2 cm due to changes related to ship channel modifications in the St. Clair River (Barko et al., 1999). Water diversions out of the Great Lakes basin are also transboundary issues that have led to disputes between Canada and the US (Reinumagi, 1986) and have garnered much public attention, especially

Michigan–Huron and Superior, coincided with large water level decreases (Gronewold and Stow, 2014), indicating that changes in climate will have dramatic impacts on the basin's water levels. For further interactions between Great Lakes water levels and climate change see Bartolai et al. (2015). Geopolitics, governance and societal values: lake level regulations and water diversion Governance and geopolitics play a large role in water quantity management within the Great Lakes basin and an assortment of management strategies exists to regulate both water levels and water diversions (and thus export) from the basin. Overall, water quantity management falls under the auspices of the Boundary Waters Treaty of 1909 and is overseen by the International Joint Commission's (IJC) Boards of Control that oversee the operations of the regulatory structures and direct outflows to protect the interests of both Canada and the US (Manninen and Gauthier, 1999). Across the basin, there are two main points where water levels are regulated: 1) at the outlet of Lake Superior at the Soo Locks-Lake Superior control structure located on the St. Mary's River (Fig. 2). This outlet has been managed by the IJC since 1921, specifically under Plan 1977A implemented in 1990 (IUGLS, 2009); and 2) at the outflow of Lake Ontario at the MosesSaunders Dam at Cornwall/Massena on the St. Lawrence River (International Great Lakes–St. Lawrence River Adaptive Management Task Team, 2013) — this is managed by the IJC and the International St. Lawrence River Board of Control (IJC, 2012) under Plan 1958DD, which has been in place since 1963 (IUGLS, 2012). Recent modifications and changes in water level regulations have been proposed for both Lakes Superior and Ontario. For Lake Superior, Plan 2012 has been proposed, which is meant to enhance Plan 1977A by: 1) improving water level preservation on Lake Superior, while taking into account the downstream lakes, should the climate become drier; 2) avoiding adverse effects on fish spawning habitat under drier conditions; 3) providing modest benefits under wetter or drier water supply conditions for commercial navigation, hydroelectric generation and coastal zone interests; and 4) reducing the month-to-month changes in flow on the St. Mary's River (IUGLS, 2012). In Lake Ontario, Plan 1958DD has recently undergone a significant re-evaluation as the IJC acknowledged that degradation of coastal wetlands and a loss of biological diversity in Lake

Table 4 Consumptive use coefficients, expressed as a percentage of withdrawn water, for the main water use categories in different regions of the Great Lakes basin (Pearson, 2011) as related to the drivers of the Great Lakes Futures Project (GLFP). GLFP driver

Demographics

Region

Use

Ontario Quebec Minnesota Wisconsin Michigan Illinois Indiana Ohio Pennsylvania New York

Demographics & Economy

Economy

Economy

Economy

Energy & Economy

Energy & Economy

Energy & Economy

Domestic use

Public supplies

Industrial use

Irrigation

Livestock

Fossil fuel plants

Nuclear power

Hydroelectric power

15 10–15 10–15 10–15 10–15 10–15 15 10–15 10 10

15 10–15 10–15 10–15 10–15 10–15 15 10–15 10 10

Varies by plant type 10 Varies by plant type 10.2 10–15 Varies by plant type 6 0–10 Varies by plant type 25

78 90 90 70 90 90 90 90 90 90

80 80 80 90 80 80 80 80 80 90

0.9 10 2 0.5–1 1–2 Varies 2 1–10 – 2

0.9 – – 0.5–1 1–2 Varies – 1–10 – 5

0 0 0 0 0 0 0 0 0 0

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concerning the potential diversion and sale of water to areas such as Midwest and Southwestern states (Morreale, 2002). Although proposals of mega-diversions in the past have been found to be infeasible, economically or technically, it should not be concluded that proposals of water sale may not be pursued again in the future (IJC, 2000). Even if mega-diversions to move water out of the basin were feasible, at least from economic and technical viewpoints, political issues related to the effective binational management of water (quality and quantity) would have to be overcome (IJC, 2000). In addition, ecological and sustainability issues would have to be considered. Tensions would be particularly acute in times of extremely low water levels or droughts (IJC, 2000). In December 2005, the Great Lakes–St. Lawrence River Basin Sustainable Water Resources Agreement and Compact were publicly released (USFG, 2008), which provides a framework for the protection of the Great Lakes basin. One of the key objectives is to forbid new water diversions out of the Great Lakes basin. Demographic demands, the economy, and energy The waters of the Great Lakes basin have drawn people for the resources that they provide for over 10,000 years (Manninen and Gauthier, 1999). The ways in which their dependent communities use them can be considered through the lens of consumptive vs. non-consumptive use. Consumptive use is the fraction of water withdrawn for a specific purpose that is not returned to the basin (Shaffer and Runkle, 2007) and is calculated by multiplying the amount of water withdrawn by a pre-determined consumptive use coefficient (expressed as a percentage of withdrawn water) for a specific water use category (Shaffer, 2008). Non-consumptive water use refers to water withdrawals or in stream uses that do not remove the water from the system, but return it in its entirety to the system (Manninen and Gauthier, 1999). These uses include transportation (shipping and navigation), hydroelectric power generation, and water-based activities (fishing and boating) (GLCR, 2014) as well as waters used in hydroelectric power generation (Pearson, 2011). The Great Lakes Commission has identified eight main consumptive water use categories for the basin that can be directly linked to some of the drivers of change for the GLFP (Table 4) and explored in a historical context. For example, the waters of the Great Lakes basin are used to meet the demands of the energy sector, and are used for processes such as metals, chemicals, paper-products manufacturing, and mineral extractions (Pearson, 2011; Shaffer, 2008). Based on 2009 data, volume-wise, public water supply and self-supply irrigation categories, which may directly relate to the economic and demographic demands of the basin's inhabitants, withdrew the most water (Pearson, 2011). Public water supply includes a range of uses such as residential, commercial, industrial, and public use, which do not supply their own

Fig. 3. Consumptive water use (Million Liters/day) by all facilities in all 10 jurisdictions in the Great Lakes basin during 1998–2009 (GLC, 2002; 2004a,b; 2005a,b; 2006a,b; 2009; 2011; Pearson, 2010a,b).

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water, and self-supply irrigation includes water used to grow crops and pastures and to maintain recreational land areas (Pearson, 2011). The largest consumptive uses within the basin, however, were for irrigation and livestock, as reflected by the large consumptive use coefficients for those categories in 2009 (Pearson, 2011; Table 4). When plotted over time (1998–2009), changes in consumptive water use are evident, with the lowest consumptive use in 2005 (at 6927 million L/d) and highest in 1998 (at 8207 million L/d) (Fig. 3). Differences in consumptive use have also been found within different jurisdictions in the basin, where the Province of Ontario and the State of Michigan had the highest water withdrawals, in comparison to Minnesota and Pennsylvania who withdrew the least during 2000– 2009 (Fig. 4). In addition, the largest water withdrawals have been in Lakes Erie and Ontario (Pearson, 2011), with total consumptive water uses in 1993, for all water use categories, reducing the levels of Lakes Erie and Ontario by 4 cm (1.57 in.) and 6 cm (2.4 in.), respectively (IJC, 2000). Looking back to look forward: how historical trends can influence future water level projections into the year 2063 To understand how existing water level trends might be extended into the future, historical (since 1963) water levels and the three key components identified that influence these water levels (over-lake precipitation, lake evaporation and land surface runoff; Figs. 5,6,7) were plotted, and trend lines were fitted to data using Microsoft Excel to provide an indication of trend direction, average magnitude of rates of change, and a basis for projection of the current trends into the year 2063 (see below). Where linear trends were determined as the best fit, the statistical conditions for applying a linear trend were assumed. The significance of these trends, permitting the rejection of the null hypothesis of a lack in trend, was also assessed at a 5% significance level. The data assessed in this study were sourced from the Great Lakes Environmental Research Laboratory (GLERL, 2012) and are described by Croley and Hunter (1994). Presented within each trend analysis are 5year moving averages in order to eliminate fluctuations over shorter time scales. Based on analysis of the above processes, the volume of water within the Great Lakes basin shows an overall declining trend of 0.6 × 109 m3/yr (p = 0.09). Although this decline in volume is not statistically significant, it is noteworthy and indicates that the region is possibly in a slightly under-resourced state. These results are consistent with the results of climate model simulations for the basin, for example Dempsey et al. (2008) looked at climate models for the basin

Fig. 4. Amount of water withdrawal (Million Liters/day) for each jurisdiction in the Great Lakes basin. For Quebec, 1993 data were used throughout because the amount of withdrawal is not considerably different. Similarly for Ontario from 2000 to 2009, data from 2000 were used (GLC, 2002; 2004a; 2004b; 2005a; 2005b; 2006a; 2006b; 2009; 2011; Pearson, 2010a; 2010b).

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Fig. 5. Five-year moving averages of the annual over-lake precipitation for the Great Lakes basin (in mm per lake surface) during 1900–2011. The trend line for the entire Great Lakes basin is shown (GLERL, 2012).

Fig. 7. Five-year moving averages of the annual land surface runoff to the Great Lakes basin (in mm per lake surface) in the period of 1940–2010. The trend line for the entire Great Lakes is shown (GLERL, 2012).

and found “10 out of 12 cases show lower water levels for Lakes Huron and Michigan; 10 out of 11 for Lake Superior.” These results are supported by Angel and Kunkel's (2010) analysis of future water levels impacts of using over 500 climate models for the Great Lakes basin, although there was high variability in the future water projections, overall they showed a decrease in water levels with time. Over-lake precipitation shows an overall increasing trend (slope of 1 mm/yr) for the Great Lakes basin as a whole, with a projected value of 50 mm in the year 2063 (Fig. 5). However, since 1986 declining trends are indicated for Lake Superior (slope of − 3.4 mm/yr, p = 0.00001) and for Lakes Michigan–Huron (slope of − 1.6 mm/yr, p = 0.005) (Fig. 5). These results are consistent with recent low water levels that have been observed in the upper Great Lakes, whereas the lower Great Lakes are at or above long-term average values (see Great Lakes dashboard, Clites et al., 2014, for current and historical hydrological data for the Great Lakes). This suggests that Lakes Superior and Michigan–Huron may be at a statistically significant risk of experiencing lower water levels in the future. The increase in overlake precipitation for the Great Lakes basin as a whole (even in light of Lake Superior's and Lakes Michigan–Huron's deviation from this trend) is consistent with the results of Kutzbach et al. (2005), who found that elevated atmospheric CO2 concentrations of the future will result in an increase in the net atmospheric moisture (precipitation–evaporation) for the Great Lakes region. Based on estimates of evaporation rates from the Great Lakes Evaporation Model (Croley and Hunter, 1994) for the last 50 years, there has

been an increasing trend in the amount of evaporation from all of the Great Lakes, with a slope of 2.8 mm/yr (Fig. 6), with sharper increasing trends in Lake Superior, with a slope of 8.1 mm/yr (p = 0.000035), and Lakes Michigan–Huron, with a slope of 5.0 mm/yr (p = 0.007) since 1997. Runoff for the entire Great Lakes basin follows an overall increasing trend (Fig. 7, slope of 1.9 mm/yr). However, the trends for Lakes Superior and Michigan–Huron are in decline (slope of − 2.4 mm/yr and p = 0.00003 since 1972; slope of − 4.0 mm/yr, p = 0.12 since 1996; Fig. 7). The declines in runoff for Lakes Superior and Michigan–Huron are consistent with the decreased precipitation noted above (Fig. 5), while the increased runoff trend for the entire basin also directly relates to the increasing trend in precipitation when all lakes are considered as one unit. In addition to the linear trends discussed above, exponential, logarithmic, and polynomial trend lines were tested with the historical data, to determine whether non-linear components were important. The results showed that the highest correlations (r2 values) were found with the linear trends, and that in most cases the other trend lines were nearly indistinguishable from the linear relationship. Having said that, in order to fully study the nature of the oscillatory signals in the time series of the lake levels and the components that affect the levels and their potential extremes, more complex non-linear models should be used, such as wavelet analysis (e.g., Mengistu et al., 2013); however, that analysis is beyond the scope of this paper. A look-ahead: future scenarios for the water quantity driver in the year 2063

Fig. 6. Five-year moving averages of the annual over-lake evaporation for the Great Lakes basin (mm) for the period 1948–2011. The trend line for the entire Great Lakes is shown (GLERL, 2012).

There is a high level of uncertainty around future water level changes in the Great Lakes basin, rooted mainly within uncertainty associated with factors influencing water levels or the water budget. The major factor contributing to this uncertainty is climate change (Changnon, 2004), with its associated changes in precipitation and air temperature. While keeping this uncertainty in mind, future natural water levels can either be similar to, drier than, or wetter than past history, and current trends may or may not dictate future scenarios. Three scenarios are explored in this paper, status quo, dystopia, and utopia, with each being a result of the interplay between natural and human factors. The status quo scenario assumes existing trends extend into the future. The dystopian scenario is one in which lower water levels result from less net water supply, poor resource management, or a combination of the two. The utopian scenario is water rich, as a result of increased net water supply and/or good resource management. The terms status quo, dystopia, and utopia reflect the present trend, the worst-case, and the best-case scenarios, respectively, and are

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discussed in relation to the current trends as illustrated in Figs. 1 and 5 to 7. Each of these scenarios is envisioned in the year 2063. Within each scenario, the reciprocal relationships between the basin's water levels and other drivers of change (the economy, energy, geopolitics and governance, demographics and societal values, climate change, invasive species, and biological and chemical contaminants, Laurent et al., 2015) are considered and summarized (Tables 5 and 6). Although these future scenarios are based on data analyses and the literature reviewed in this paper, they are mainly qualitative in nature, informed not only by the outputs of models, but also are creative exercises that reflect the informed GLFP discussions and ideas. For the status quo scenario, projecting the above-calculated drop of 0.6 × 109 m3/yr 50 years into the future results in an average drop in water level for all lakes of approximately 12 cm, assuming the total surface area of the lakes is 244,196 km2. This value is considered reasonable for the purpose of this study, relative to projections of water level by Angel and Kunkel (2010) of − 3 m to + 1.5 m for the Great Lakes basin in 2080–2094. Scaling these figures back to 2063 suggests a range of approximately −2.1 m to +1.1 m, and these values will be assumed for the dystopian and utopian future scenarios, respectively. Scenario 1. Status quo: current water level trends continue into the future, a case of moderate water level decline In the status quo scenario, the historical trends from 1963 to 2013 have continued into the year 2063 and overall the volume of water within the Great Lakes basin has dropped by 30 × 109 m3, resulting in a decrease in water level for the entire basin of 0.12 m. Climate remains the main factor influencing this slightly decreased water level state in 2063, through the dominant role that precipitation (Croley et al., 1996) and evaporation (Assel et al., 2004) play in the basin's water balance. From 2013 until 2063, the basin as a whole experienced an overall increase in precipitation (+50 mm in 2063) and runoff (+95 mm in 2063). However, Lakes Superior and Michigan–Huron continue experiencing decreased over-lake precipitation and land surface runoff in 2063 (Figs. 5 and 7). The impacts of this decreased over-lake precipitation and land surface runoff have been pronounced for the basin, and have resulted in decreased water levels in Lakes Superior and Michigan–Huron. This condition, in turn, has reduced downstream flow and caused a drop in water levels in Lakes Erie and Ontario. Furthermore, although the basin experiences increased over-lake precipitation as a whole in 2063, the evaporative loss trends from 1963 to 2013, based on data estimates from the model of Croley and Hunter (1994), continue (Fig. 6), due to increased air temperature and decreased ice-cover (Dempsey et al., 2008). The impacts of decreased water levels on the basin's economy, energy generation and important industries can be felt across the basin in 2063. For instance, reductions in outflow in 2063 at the Niagara and St. Lawrence River hydropower stations have resulted in a reduction in hydropower generation capacity and millions of dollars in annual loss to the US and Canada similar to those projected by Bates et al. (2008). Furthermore, the declines in lake levels have had major effects on the Great Lakes shipping industry over the past 50 years. Each 1000-foot-long vessel had to decrease its cargo-shipping capacity at values similar to those listed by the Great Lakes Carrier's Association of 270 tons of cargo-shipping capacity lost per inch of water level decrease (Lindeberg and Albercook, 2004). Limited access to water for recreational facilities has also negatively impacted coastal tourism (IUGLS, 2012). In particular, marinas are continually facing challenges as their slips have become unusable or unable to accommodate the size of boats for which they were designed, their boating infrastructure (docks, piers and seawalls) has become exposed or damaged, and overall recreational boating activity has decreased due to increased wait times resulting from limited channel access and boater traffic bottlenecks (IUGLS, 2012). Under the decreased water level trends from 2013 to 2063, recreational boaters have encountered an increasingly high risk of running aground when entering or leaving the water,

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which has necessitated increased dredging, which is the most common approach to managing lowered water levels in marinas, harbors and channel-ways (Lindeberg and Albercook, 2004). The effects of water levels on biological ecosystems are also more evident at the low water levels of 2063. In 2063, many of the sediments and plants surrounding the Great Lakes shorelines are exposed to air, which was shown by Hudon et al. (2006) to cause disconnected wetlands and negatively impact the habitats of plants and animals that depend on wetlands. Furthermore, the basin experiences magnified water quality issues under the lower water levels of 2063 (AMTWG, 2012). One such cause of these decreases in water quality has been the increased dredging in many of the basin's ports, marinas and harbors, which has resulted in operation and environmental costs due to the contaminated nature of much for the dredged sediment from industrial water spills, and the high cost of dredging itself (Lindeberg and Albercook, 2004). The moderate case of permanent water scarcity that characterizes this status quo scenario has put a strain on the basin's governing bodies, governing policies and societal values. The water level declines seen in 2063 have resulted in an increase in the beach areas of the basin, generating many shoreline conflicts. As forecasted by Dempsey et al. (2008), a significant conflict under these conditions has stemmed from newly exposed beaches and public access in areas where private lakeshore property owners wanted to maintain control, which has led to many claims and counterclaims of ownership by the public and private sectors. In addition, increasing strain has been placed on the basin from water deplete areas within Canada, the US, and other parts of the world. All of these problems have highlighted the importance of the Great Lakes– St. Lawrence River Basin Sustainable Water Resources Agreement and Compact to decision makers, and that policy is still in place, effectively preventing new water diversions and export out of the Great Lakes basin. Scenario 2. Dystopian future: extreme water level decreases In this dystopian scenario, the historical trend of declining water levels throughout the basin from 1963 to 2013 has continued at an accelerated rate into the year 2063 and all of the Lakes have experienced a decrease of water level of 2.1 m. In essence, virtually everything is worse for the basin, in comparison with the status quo scenario. The extremely low water levels of 2063 in the basin are a result of the changing climate from 2013 to 2063, where elevations in temperature and reduced ice-cover have driven increased evaporation, as was the case for the dramatic declines in Great Lakes water levels seen in the late 1990s (Assel et al., 2004; Gronewold and Stow, 2014). During this water scarce future, poor governance has also compounded the problem, where adaptive management strategies have not been followed, and water conservation policies have not been implemented or enforced. Under the decreased water levels of 2063, water scarcity problems prevail and limit access to water. As a result, water is viewed in the basin as a scarce and expensive resource. In 2063, the economy of the basin is struggling due to dramatic declines in hydropower generation (Bates et al., 2008), threatened water supplies, limited tourism (IUGLS, 2012), restricted shipping navigation capacity, and increased risks to industries that rely on the lakes as a source of process and cooling waters (Gronewold and Stow, 2014). In 2063, the impacts of decreased water levels on the shipping industry are seen with many more ships working with less-than-full cargo loads, which results in higher operational costs and, in turn, more expensive goods. Trade in the US and Canada has suffered as a consequence, as well as the import and export of goods between the Great Lakes region and foreign countries. Many jobs have also been lost in the basin due to the impacts of the extremely low water levels. Once again the shipping industry acts as a sentinel for this job loss, as many individuals lost their jobs when the main means of cargo transport shifted from water to rail and truck, which was an adaptive approach necessary for the basin to take in light of the

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Table 5 Impacts of Great Lakes basin driving forces on the water quantity driver. Driver

Driver's impact on water quantity driver

Driver's impact on water quantity driver

Climate change

Increased temperature increases evaporation and decreases water levels in all of the Great Lakes.

Governance and geopolitics

Government authorities can regulate the amount of water being diverted into or out of the Great Lakes basin, thereby either increasing or decreasing water levels.

Economy

A thriving economy will increase water demand. The implications of better economic conditions are manifested in better tourism, more migration into the Great Lakes basin area, more commercial and industrial development, and overall more energy demand, with associated demands on water. Consumptive use coefficients for water withdrawals are highest for irrigation and livestock sectors. Power sectors also withdraw large amounts of water-consumptive coefficients depend on the type of power plants. During extreme low water levels, challenges in generating hydroelectric power will be seen. As a consequence, electricity rates may go up.

Increased temperature and evaporation have caused declining trend in precipitation and runoff in Lakes Superior and Michigan–Huron since 1986. Government authorities should be able to develop plans for water conservation, for example, incentive programs for better irrigation practices, water-efficient equipment installations, etc. n/a

Energy

Biological and chemical contaminants Aquatic invasive species Demographics and societal values

n/a

Increasing population and economic growth may cause an increase in water withdrawals needed to support the different types of power plants (note: most electrical power is generated by thermal power plants). However, significant increases in water use for electricity generation may not occur, because most water withdrawn for cooling purposes is returned to the basin. n/a

n/a

n/a

As the population is expected to grow, water demand and consumption should also n/a increase (note: effects of anthropogenic activities on water quantity/level in the basin are much less than the effects of natural factors).

decreased water levels (Lindeberg and Albercook, 2004). Not only did the shift from water to rail/truck have impacts on the employment trend in the basin from 2013 to 2063, it also had negative impacts on the environment due to increases in fossil fuel use for these less fuelefficient methods (Lindeberg and Albercook, 2004). Environmental impacts of the decreased water levels throughout the basin include contaminant release due to the increased dredging under low water levels (Lindeberg and Albercook, 2004), as well as ruined wetland environments. As a result, the population and diversity of living species in the Great Lakes region (e.g. fish and their spawning habitats, migrating birds and aquatic plants that depend on wetlands (Mandrak, 1989; Mandrak and Cudmore, 2010)) are at extreme risk. The tourism and recreation industries within the basin are suffering in 2063, as a result of reductions in recreational boating due to limited access to piers and harbors (Lindeberg and Albercook, 2004). Furthermore, reductions in fisheries and waterfowl dependent activities, such as hunting and fishing have occurred due to the loss of wetlands. However, in 2063, beach area has increased due to the exposure of previously covered sands by decreased water levels (GLANPS, 2007), although this increase in beach area has not been enough to

accommodate for the losses in the recreational boating, hunting, and fishing industries. The extreme case of water scarcity experienced in the basin in 2063 has put a strain on the basin's governing bodies and governing policies. In particular, heavy pressure has come from the Great Plains and the Rocky Mountain regions of North America, as the reduction in water supplies in those areas due to reduced winter snowpack and early spring runoff have made water-dependent agriculture and industry very expensive (Dempsey et al., 2008). As a result of an increase in public outcry and pressure on politicians, the Great Lakes–St. Lawrence River Basin Sustainable Water Resources Agreement and Compact was revised and now allows regulated water export from the basin to sustain water poor regions, which has led to further water level declines in the basin. Scenario 3. Utopian future: abundant water In this scenario, the historical trend of declining water levels from 1963 to 2013 was reversed, and the Great Lakes basin as a whole experienced a water level increase of 1.1 m in 2063, which is consistent with the potential reality for the basin modeled by Lofgren et al. (2011). The

Table 6 Impacts of water quantity driver on other driving forces in the Great Lakes basin. Driver Water quantity condition

Climate Governance and geopolitics change

Abundant n/a water

Water scarcity

n/a

The government needs to manage excess flow, including damages caused by excessive water. Authorities must also anticipate proposal of mega-water diversions. Government makes arrangements to control water consumption (e.g. water pricing system) and reduce water diversion out of the basin.

Energy

Economy

Biological and chemical contaminants

Aquatic Demographics invasive and societal species values

Power plants can work at full capacity.

Economic growth is expected from growing industries (e.g. transportation, bottled water).

n/a

n/a

Potential to attract more residents to the region.

Hydropower plants and electricity generation will face challenges; plants cannot operate at full capacity.

Economy is affected through increased water and electricity prices, and operational costs for shipping and navigation, and decreased tourism and recreational activities, with resulting increased job loss.

Low lake levels result in increased dredging for shipping which has the potential to release contaminants from sediment.

n/a

Potential for a decrease in population growth rate, or even in population.

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higher water levels are a result of increased net moisture in the atmosphere (Kutzbach et al., 2005) and elevated precipitation within the region, which have resulted in increased annual stream flow (as projected by Cherkauer and Sinha (2010) for the Lake Michigan region into the late century (2079–2090)), thereby increasing supply into the lakes. Under this abundant water future of 2063, the economy around the basin thrives and people flock to the region to benefit from this economic boom. Benefits of the maintained higher water levels have been felt from 2013 to 2063 by the navigation and hydropower generation industries due to decreased demands for dredging, increases in available draft (distance between water's surface and vessel bottom), and the reliability of an appropriate water supply for energy generation (Quinn, 1981). Estimates of Bates et al. (2008) on the benefit of water availability for hydropower have been realized — approximately $25 million (Canadian) per year. The shipping and navigation sectors benefit from the ability to operate ships at full capacity. Furthermore, tourism and recreational activities are thriving, as the increased water levels have kept marinas and ports functional (Lindeberg and Albercook, 2004), and spawning grounds for important fisheries, such as trout, have been maintained under the water rich conditions. Birding and hunting also thrive, as the higher water levels have maintained wetlands important for waterfowl nesting grounds. The increase in water levels has necessitated changes in the governing management plans for the region. These changes are a direct result of the increased risk of coastal areas to erosion, shoreline damage (Quinn, 1981), and flooding damage, as well as their associated economic and social impacts (IUGLS, 2012). Although high water levels may cause damage, efficient flood mitigation and management strategies are in place, and sound management oversees shoreline constructions and different land uses in order to significantly minimize risk. The six core elements of an adaptive management strategy recommended by IUGLS (2012) are in full effect across the basin in 2063 and water level regulation has been improved. Good monitoring and early warning systems are in place to monitor the water levels in the Great Lakes basin and to consider effective ways to keep the water levels within acceptable limits. More gauging stations to record precipitation, evaporation, and water level fluctuations in the basin have been established in an effort to better address the effects of influential climatic factors on water levels, and to incorporate better data into adaptive management schemes. The existence of good governance under the abundant water scenario helps stakeholders make informed and sound management decisions related to their properties and infrastructures. There is ample public money for monitoring and data analysis programs to support basin management. Conclusions Changes in water levels in the Great Lakes basin have been driven by both natural factors and human activities. This study evaluates the mean annual trends of the different natural climatic factors that affect the water levels in the basin and connect them to future scenarios that suggest the impacts of these trends on the social, economic and environmental aspects of the basin into the year 2063. Climate change impacts basin water levels through its influence on increased surface water temperature, a gradual disappearance of ice cover, and the continuous increase in evaporation from all of the Great Lakes. Furthermore, a decline in precipitation, which is prevalent for Lakes Superior and Michigan–Huron since 1986, reduces water levels of the individual lakes, and affects the distribution of water between the lakes. Although not explored in this paper, we recognize the spatial and temporal variation that differences in climate within the basin have on the water levels in the lakes and recognize its importance when understanding future water level changes for the basin. Human activities impact Great Lakes water quantity through the processes of consumptive water use by different interests, inter-basin

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water diversions, and water level regulation plans. As the population is expected to grow, demand on water also is expected to increase. Strong social drivers (such as the economy and societal values) also relate to changes in water levels in the Great Lakes basin, because changes in the levels have important economical, societal, environmental, and ecological consequences (Tables 5 and 6). The possible futures in the year 2063 related to water quantity depend on the nexus among the multiple drivers of change operating within the Great Lakes basin (Laurent et al., 2015). Overall, the future of the basin's water depends on the nexus among these drivers. It is recognized that extremely low or high water levels are not desirable for the basin, as both natural components and humans have adapted to a certain range of water levels, and will face difficulties during extremely low or high water levels. If current trends in climatic factors were to continue, it is likely that the Great Lakes basin will experience lower water levels in the future. Recommendations High uncertainty exists in predicting future water levels in the Great Lakes basin. A major challenge faced by the current regulation plans include accommodating for the uncertainty in water level fluctuations while at the same time fulfilling the needs of different water users in the basin. Based on these uncertainties, we support an adaptive management approach be taken to better regulate water levels (AMTWG, 2012) and adapt to changes through continuous monitoring, assessment, and revising information as new knowledge becomes available. We also recommend that strong collaborations between stakeholders (governmental bodies, business, and individuals) be cultivated, so that future issues related to water quantity in the basin can be solved collectively. In particular, we support the following actions for consideration to help navigate potential problems associated with the high uncertainty of water level predictions in the basin, and to achieve a socio-ecologically sustainable future for the basin: (1) continue to support and develop water level and climate data monitoring systems within the basin based on data records and models to understand the current and possible future conditions of water levels/volume in the basin; (2) apply risk management techniques to inform management decisions around water level management in the future; (3) address the effects of intraannual and inter-annual components of the climatic factors affecting the water level in greater detail; (4) continue support of effective and efficient binational coordination between Canada and the US to promote good governance around water level management; (5) involve stakeholders from diverse backgrounds in management decision-making around basin water level regulation; and (6) incorporate a systems approach to understanding the interrelationships among the natural and anthropogenic factors influencing the basin's water levels. Acknowledgments The authors thank the leadership group of the Great Lakes Futures Project (GLFP) for providing the opportunity to take part in this important initiative. The GLFP is funded by the Transborder Research University Network (TRUN), GLFP supporting universities, Environment Canada, Michigan Sea Grant and New York Sea Grant. We also acknowledge funding from the Canada Research Chair Program (950-228034) and NSERC's Canadian Network of Aquatic Ecosystem Services (417353-2011) grants funded to Dr. Irena Creed, which provided graphic and editorial support for this article. The authors thank Dr. J. Bulkley from the University of Michigan and Dr. J. Bruce from the Advisory Group of the IUGLS for their mentorship efforts during early development of this article. The authors thank the GLFP internal reviewers, Drs. I. Creed, G. Krantzberg, K. Friedman, D. Scavia and J. Miller, and the anonymous external reviewers. The authors would also like to

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