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Blue water scarcity in the Black Sea catchment: Identifying key actors in the water-ecosystem-energy-food nexus
Environmental Science & Policy 66 (2016) 140–150
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Blue water scarcity in the Black Sea catchment: Identifying key actors in the water-ecosystem-energy-food nexus M. Fasela,* , C. Bréthauta , E. Rouholahnejadb , M.A. Lacayo-Emerya , A. Lehmanna a b
University of Geneva, Institute for Environmental Sciences, Bd. Carl-Vogt 66, CH – 1211, Geneva, Switzerland Department of Environmental Systems Science, ETH Zurich, Universitaetstrasse 16, CH – 8092, Zurich, Switzerland
A R T I C L E I N F O
Article history: Received 18 February 2016 Received in revised form 2 August 2016 Accepted 10 September 2016 Available online xxx Keywords: Water Scarcity Nexus Ecosystems Energy Food
A B S T R A C T
Large-scale water scarcity indicators have been widely used to map and inform decision makers and the public about the use of river flows, a vital and limited renewable resource. However, spatiotemporal interrelations among users and administrative entities are still lacking in most large-scale studies. Water scarcity and interrelations are at the core of the water-ecosystem-energy-food nexus. In this paper, we balance water availability in the Black Sea catchment with requirements and consumptive use of key water users, i.e., municipalities, power plants, manufacturing, irrigation and livestock breeding, accounting for evaporation from major reservoirs as well as environmental flow requirements. We use graph theory to highlight interrelations between users and countries along the hydrological network. The results show that water scarcity occurs mainly in the summer due to higher demand for irrigation and reservoir evaporation in conjunction with relatively lower water resources, and in the fall-winter period due to lower water resources and the relatively high demand for preserving ecosystems and from sectors other than irrigation. Cooling power plants and the demands of urban areas cause scarcity in many isolated locations in the winter and, to a far greater spatial extent, in the summer with the demands for irrigation. Interrelations in water scarcity-prone areas are mainly between relatively small, intra-national rivers, for which the underlying national and regional governments act as key players in mitigating water scarcity within the catchment. However, many interrelations exist for larger rivers, highlighting the need for international cooperation that could be achieved through a water-ecosystem-energy-food nexus. ã 2016 Elsevier Ltd. All rights reserved.
1. Introduction Water scarcity is a growing concern in many parts of the world as it leads to conflicts, overexploitation of aquifers, increased pollution, alteration of ecosystems, and various negative effects on human health, food and goods production, and economic wellbeing (Jury and Vaux, 2007; Kummu et al., 2010). Water scarcity is both a natural and anthropogenic phenomenon (Jaeger et al., 2013). It can be caused not only by unfavorable climate changes and the failure of a society to adapt but also by excessive and increasing water demand vital to sustaining population growth, industry and agriculture. Moreover, water infrastructure can change the temporal pattern of streamflow, and
* Corresponding author. E-mail address: [email protected] (M. Fasel). http://dx.doi.org/10.1016/j.envsci.2016.09.004 1462-9011/ã 2016 Elsevier Ltd. All rights reserved.
human activities that consume water through evaporation or incorporation into products eventually deplete a significant amount of resources from the hydrological system (Hoekstra et al., 2012). There has been a growing recognition that ecosystems are a central and legally established water user, and in 1982, the World Charter for Nature imposed further reductions to water use in nation states committed to their protection. Consequently, competition for available resources is likely to increase (FAO, 2012). This raises the need to decrease water demand, improve the efficiency of water consumption, and lessen the impacts of consumptive use and streamflow regulations to ensure a balance between socioeconomic development and environmental protection (Hamdy et al., 2003). At the Bonn 2011 Nexus Conference, the concept of a water nexus, which allows for causal links between users and their common resources in water management plans (Hoff, 2011), was
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identified as an innovative way to mitigate water scarcity. The purpose of this approach is to encourage cooperation, reduce trade-offs, and improve consumption efficiency and cross-sectorial policy coherence so that undesirable effects from water use or climate change can be reduced (Bazilian et al., 2011). To this aim, evaluating nexus structures and dynamics in a geographical area allows for the prediction of potential conflicts or opportunities for synergy among users (Wolf, 2007). The Black Sea catchment suffers from water scarcity in many areas and is subject to a complex set of interrelations involving 23 countries, many different types of users, and four important international river basins. The need for improving ecological conditions and managing growing conflicts of interest in the area (GIWA, 2011) requires regional coordination by the existing national and international institutional framework, including the Black Sea Commission and the International Commission for the Protection of the Danube River (Myroshnychenko et al., 2015). Indeed, water scarcity can be a trigger for cooperation among countries instead of a source of conflict, primarily in situations where institutional frameworks exist (Gizelis and Wooden, 2010) and if scarcity is not extreme, but moderate (Dinar, 2009). A few global and regional studies have assessed water availability, use and scarcity in the catchment (Baer et al., 2015; Floerke et al., 2012; Hoekstra et al., 2012; Karabulut et al., 2015; Lehmann et al., 2015). Although some of these reports localize users, none have examined upstream-downstream interrelations in detail. Interrelations are at the core of the nexus concept. In this paper, we identify interrelations along the hydrological network using graph theory (Gould, 2012). We focus on so-called surface “blue water” (Falkenmark and Rockstrom, 2006) that is available in rivers. We intend to answer the following questions:
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As a transnational entity, the catchment covers parts of 23 countries1, and is inhabited by more than 180 million people (UNEP, 2013; World Bank, 2015). Municipalities, industries, and agriculture are all major water users, depending on region (FAO, 2013), and ecosystems preservation has been legally recognized in all countries (Paleari et al., 2005). The catchment is subject to various international water treaties and policies. The major international agreements are established by the Black Sea Commission (BSC) in the coastal states, the International Commission for the Protection of the Danube River (ICPDR) in the Danube river basin, and the Water Framework Directive (WFD) in the European Union and candidate countries (Paleari et al., 2005). The catchment was the focus of European research project enviroGRIDS (Lehmann et al., 2015) between the years 2009 and 2013, which aimed at building the capacity for this region to use and share earth observation data to support sustainable development (Giuliani et al., 2013). The present work builds on the outcomes of this project, primarily the hydrological model for the entire Black Sea catchment realized at sub-basin and daily temporal resolution (Rouholahnejad et al., 2014). 2.2. Frameworks of analysis
2. Methods
This work was accomplished in several consecutive steps, linked as in Fig. 2. (1) First, we assessed river flows (RF) with the Soil and Water Assessment Tool (SWAT) (Rouholahnejad et al., 2014). (2) Then, we estimated water withdrawals (WW) and consumptive use (WC) for municipalities, power plants, manufacturing, irrigation, and livestock breeding. (3) Adding WC to RF, we estimated the naturalized river flow (NRF). NRF is then used to assess environmental flow requirements (EFR), i.e., the part of flow necessary for preserving critical ecosystem structures and functions. The remaining NRF after allocation of EFR is the quantity of water available (WA) for human use without harming the environment. (4) We then allocate water consumptive use (WC), i.e., the evaporation or incorporation into products of human activities. Next, we compare water withdrawals (WW) of human activities with the remaining available water to identify sub-basins and periods of water scarcity through water scarcity indices (WSI). (5) We identify upstream-downstream interrelations among users and countries using surface water as an entry point for defining nexus structures in the Black Sea catchment on the ground as it is a common resource to all users. We subdivided the Black Sea catchment into the 23 national territories mentioned previously, nine main river basins2 and 12,982 sub-basins of 100 km2, the latter having been defined by hydrological modeling (Rouholahnejad et al., 2014). These subbasins were the smallest units of analysis and were subsequently aggregated into river basins, national territories, or catchments when required (Fig. 3). As water availability and requirements vary widely throughout the year, we used a monthly time scale to take into account these variations.
2.1. Study area
2.3. Water availability
The Black Sea catchment is situated in the Northern hemisphere at the interface between Europe and western Asia. It covers an area of approximately 2.4 million km2 and includes four important transboundary river basins: the Danube, the Dnieper, the Dniester, and the Don (Fig. 1). The catchment is home to a large variety of topographic and climatic conditions ranging from temperate and alpine areas in the west, continental and steppe regions in the north and the east, and Mediterranean and semi-arid areas in the south.
Rouholahnejad et al. (2014) modeled blue and green water availability with the Soil and Water Assessment Tool (SWAT)
Where and when is water scarcity most likely to occur in the Black Sea catchment? What countries and users are involved in these water scarce areas and what are their upstream-downstream interrelations? How can such analysis be employed in a nexus framework to mitigate water scarcity in the Black Sea catchment? To answer these questions, we spatiotemporally balanced water availability with environmental flow requirements, as well as water withdrawals and consumptive use by the main types of water users, specifically municipalities, energy, manufacturing, irrigation, and livestock breeding while taking into account evaporation from major reservoirs. Then, we identify existing upstream-downstream interrelations among countries and types of users using a directed acyclic graph (DAG) (Gould, 2012) of the river network. The users and countries identified as key players should be given priority to mitigate water scarcity in the catchment by implementing a nexus regulatory framework.
1 Albania, Austria, Belarus, Bosnia and Herzegovina, Bulgaria, Croatia, Czech Republic, Georgia, Germany, Hungary, Italia, Macedonia, Moldova, Montenegro, Poland, Romania, Russia, Serbia (incl. Kosovo), Slovakia, Slovenia, Switzerland, Turkey, Ukraine 2 Danube, Dnieper, Dniester, Don, Kelkit, Kizil, Kuban, Rioni, Southern Bug
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Fig. 1. Map of the Black Sea catchment: (a) general location and (b) main geographical features.
(Arnold et al., 2012) at the sub-basin spatial scale and with daily temporal resolution for the entire catchment. In the present study, surface water availability was defined as river flow, which is formed by accumulation along the hydrological system of the subbasin water yield. Water yield is the net amount of water that is equivalent to surface runoff, lateral flows, and groundwater from shallow aquifers contributing to streamflow minus losses through the streambed and evaporation. Monthly averages of river flows for the period of 1990–2006 were obtained from this model and used for analysis. The model takes into account the spatial and temporal dynamics of land use and was intended to represent water-related processes in their natural state. Dam and reservoir management as well as water diversion data were usually not available in most of the catchment and were not included in the hydrological modeling. We also assumed that the model implicitly accounted for water consumption as it was calibrated against recorded gauge observations. Accordingly, the naturalized river flow, i.e., the flow that would exist without human consumptive use (Doell et al., 2009; Haddeland et al., 2014), was approximated by adding water consumptive use to the modeled flow. 2.4. Water needs and consumptive use 2.4.1. Environmental flow requirements The river flow regime, which involves the flow magnitude, frequency, duration, timing, and predictability, is the principal force that determines many fundamental natural ecological characteristics of river ecosystems extreme events, low and high-flow seasons that shape habitats, species distributions, and
ecosystem functioning (Lytle and Poff, 2004; Poff and Zimmerman, 2010). Consequently, establishing river flows within a range that maintains beneficial ecological status is of prime importance to preserve stream and riparian flora and fauna. To assess this quantity, we used the “Variable Monthly Flow (VMF)” method (Pastor et al., 2014), assuming a “fair” level of protection policy to determine monthly environmental flow requirements (EFR) in relation to monthly natural flow variability. A “fair” level of protection policy allows for multiple disturbances to occur so that socioeconomic development can be supported and is the lowest level of acceptable protection from a water management perspective (Smakhtin et al., 2004). Low, intermediate and high-flow seasons were defined by classifying months into groups with a mean flow under 40%, between 40%–80% or above 80% of the mean annual flow, respectively. As relatively more water is required for ecosystems during low-flow periods compared to high-flow periods, flow reserved for ecosystems was fixed at 60% during low-flow, 30–60% during intermediate-flow, and 30% during high-flow seasons, hence allocating 40, 40–70, and 70% of the monthly mean flow for other uses, respectively (Pastor et al., 2014). Like (Richter et al., 2012), these percentages of water allocated for the environment can be observed as a default protection policy, as more detailed, sound assessments have not yet been conducted for any particular river. 2.4.2. Sectorial withdrawals and consumptive use The methods employed to estimate withdrawals by sectors were derived from other studies (Floerke and Alcamo, 2005; Floerke et al., 2013). Consumption was defined as the ratio of withdrawn quantities not returning to the environment after use
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Fig. 2. Conceptual framework for the analysis of the nexus structure in the Black Sea catchment.
either by evaporation or incorporation into products, therefore unavailable for reuse downstream. The time series were obtained from FAO, UNICEF, World Bank, state statistical office databases, and the literature for the period of 1990–circa 2014 (Supplemental Information, Appendix A and B for more detail on data and calculations). The withdrawals by municipalities were calculated using urban and rural population densities (CIESIN, 2011), rates of connection to running water supply systems (WHO and UNICEF, 2013), and national domestic water withdrawal intensities. Water consumption was assumed to be 10% of this quantity (Hoekstra et al., 2012). Withdrawals and consumptive use for cooling power plants were calculated with consideration of electricity generation, fuel type3 , and the cooling systems4 of 3604 plants (Davis et al., 2012; GEO, 2014). Water withdrawal and consumption intensities for each combination of fuel type and cooling system were obtained from the literature (Davies et al., 2013; Macknick et al., 2012). The water requirements for manufacturing were acquired from national statistics and downscaled according to urban population density.
3 Nuclear, coal, gas, combined-cycle, oil, biogas, biomass, geothermal, solar, waste, wind, and hydropower. 4 Once-through or closed-loop cooling, including tower or ponds when available. 5 Wheat, maize, rice, barley, rye, millet, soybeans, sunflower, potatoes, sugar beet, rape seed/canola, groundnuts/peanuts, pulses, citrus, grapes/vine, cotton, others perennial, fodder grasses, and other annuals.
Water consumption for this sector was assumed to be 10% of withdrawals (EC, 2014). Net irrigation water requirements for 19 types of crops5 present in the catchment were obtained from Siebert and Doell (2008) and temporally allocated using the same crop coefficient method as in aus der Beek et al. (2012) using a daily Penman-Monteith equation. A country-specific irrigation efficiency factor (aus der Beek et al., 2010; Rohwer et al., 2007) was applied to obtain gross irrigation withdrawals. A consumptive use of 80% was assumed (Nixon et al., 2003). Withdrawals for livestock breeding were estimated using cattle, goat, sheep, pig, and poultry densities (FAO, 2013; Robinson et al., 2014), as well as dominant livestock production systems (Robinson et al., 2011). Withdrawal intensities for each combination of breeding and production systems were derived from Chapagain and Hoekstra (2003) with an assumed consumptive use of 15% (De Roo et al., 2012). In the absence of monthly data, withdrawals and consumption for all sectors, except for irrigation, were assumed to remain constant during the year and to vary only interannually. Irrigation is highly seasonal in the catchment, as described in section 3.1. Improvements have yet to be made for modeling the seasonality for other users, notably power plants. Evaporation from the 238 large reservoirs listed in Lehner et al. (2011), supplemented by 87 additional reservoirs in the ECRINS (EEA, 2012) and GeoNames (GeoNames, 2015) databases, was estimated assuming a daily evaporation that is 10% higher than the reference evapotranspiration throughout the entire year
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Fig. 3. Map of the hydrological network used for the analysis. It comprises nine main river basins and 12,982 reaches, representing each sub-basin with an area 100 km2.
(Hoogeveen et al., 2015). Daily reference evapotranspiration was computed by the SWAT model using the Penman-Monteith equation. We assumed that the effects of water consumption within a month are limited to that month.
The following representative scale was then used: WSIc <0.2: No scarcity; 0.2–0.3: Low; 0.3–0.4: High; >0.4: Very high. Blue water scarcity using the demand index was estimated using the quotient of total withdrawals by surface water available for human use (Smakhtin et al., 2004):
2.5. Water scarcity
WSIw ¼
We used two complementary scarcity indices in this study. The first is focused on consumption and how its reduction of water flow can threaten downstream ecosystems and users. The second addresses demand, i.e., withdrawals, and how water availability can be insufficient even independently of upstream consumptive use. Blue water scarcity using the consumptive index was estimated from the quotient of upstream consumptive use divided by surface water available for human use (Hoekstra et al., 2012):
where WSIw is the water demand scarcity index [] and WW is the water withdrawals in m3 month1. The following representative scale was then used: WSIw <0.1: No scarcity; 0.1–0.2: Low; 0.2–0.4: Moderate; 0.4–0.8: High; >0.8: Very high.
WSIc ¼
UWC UWC ¼ WA NFR EFR UWC
ð1Þ
where WSIc is the consumptive use scarcity index [], UWC is the total water consumption in upstream sub-basins, WA is the water available without harming ecosystems, NRF is the naturalized river flow, and EFR is the environmental flow requirements, with all variables in m3 month1 except for WSIc, which is dimensionless.
WW WW ¼ WA NRF EFR UWC
ð2Þ
2.6. Upstream-downstream interrelations Interrelations were analyzed using a directed acyclic graph (DAG) of the hydrological network built in R with the igraph package (Csardi and Nepusz, 2006), integrating the above results. Sub-basins and reaches were defined as vertices and edges of the graph, respectively. To determine interrelations, all of the sub-basins of each country were selected, and for each sub-basin in a given country, we searched for the main upstream impacting sectors and countries as well as the main downstream inquiring sectors and countries.
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For interrelations in water scarce sub-basins, we only selected sub-basins with a high water scarcity index, i.e., WSIw 0.4 or WSIc 0.3. Two matrices, one for consumptive use and one for withdrawals, were filled during this process to gather the results between each possible pair of countries. Interrelations were computed solely based on water quantity consumed and withdrawn. We considered interrelations to be bidirectional. Indeed, upstream users impact downstream users through consumptive use, while downstream users can also impose constraints on water allowed to be depleted upstream through cooperative agreements. We represent these interrelations between countries using diagrams that emphasize bilateral relations. The diagrams must be interpreted from a cooperative perspective, showing that both upstream consumptive use and downstream water needs should be reduced to mitigate water scarcity. 3. Results 3.1. Spatiotemporal representation of water scarcity Most of the estimated 467 billion m3 year1 of surface water is available during the spring, when there is approximately twice as much water as the rest of the year, less abundant periods being the end of summer and middle of winter (Fig. 4a and b). The Danube basin represents about 50% of all annual available water, the Dnieper 16%, the Don 10% the Kuban 4.6%, and the Dniester 2%, with 17.4% in other river basins with no one having more than 2%. On average, naturalized flow was 5% higher than modeled river flow, representing 495 billion m3 year1 (Supplemental Information, Appendix C). Approximately 40% of this water, i.e., 209 billion m3 year1, had to be reserved for freshwater ecosystem preservation, allowing 258 billion m3 year1 for other uses. On this amount, human activity sectors withdraw an estimated 77 billion m3 year1, with industry as the largest user at 45% (30% for cooling power plants and 15% for manufacturing). Other uses included 35% for irrigation, 19% for municipalities (12% for urban areas and 7% for rural regions), and 1% for livestock breeding. Consumptive use was estimated to reach 32 billion m3 year1, with 58% used for irrigation, 32% by reservoirs evaporation, 4.8% used in municipalities, 2.2% used for livestock breeding, 1.7% used in manufacturing, and 1.3% used for power plants. Irrigation shows a strong seasonal pattern as most irrigated crops start growing in May and continue to grow while increasing
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their water needs until harvest season in August or September. Similarly, reservoir evaporation is the highest during this same period. Therefore, water withdrawals and consumption are almost entirely from other sectors during most of the year, with irrigation and reservoir evaporation adding their effects mostly during the summertime (Fig. 4a and b). As a result of these temporal shifts between water availability and use, there are two major periods where water scarcity is high: 1) the summer, due to the higher demand from irrigation, consumptive use from irrigation and reservoirs, and reduced water resources, while demand from other sectors remains constant; and 2) the fall-winter period, due to reduced water resources and a higher demand for ecosystem preservation and sectors other than irrigation (Fig. 4a and b). This seasonal pattern is generally true for all river basins within the catchment, although it varies in amplitude and length, leading to water scarcity in different areas with varying degrees of severity and duration that affect many users. Indeed, further spatial disaggregation shows that the spatiotemporal distribution of major water users, as well as scarcity, varies considerably among regions on an annual (Fig. 5) and monthly (Supplemental Information, Appendix E and G) basis. In particular, cooling power plants and the demands of urban areas cause scarcity in many isolated locations in winter and, to a far greater spatial extent, in the summer with the demands of irrigation (Appendix E). 3.2. Upstream-downstream interrelations Graph analysis shows that there are many mutual interrelations between countries. The hydrography and national border configurations are such that two countries can be upstream and downstream to each other simultaneously. These intricacies must be analyzed at the sub-basin scale to be detected. Often, though, these relations are asymmetric in terms of quantity, meaning that one country can outweigh the other regarding consumptive use and requirements (Fig. 6a and b). Disaggregating Fig. 6, interrelations among all possible users and pairs of countries can be summarized as in Fig. 7. As an example, we can determine interrelations between Bulgaria and Romania: Bulgaria consumes water upstream mainly through reservoir evaporation, irrigation, and municipalities (uBGR), whereas Romania’s downstream water requirements are mostly for electricity generation (dROM). In addition, Romania consumes water upstream mainly from reservoirs and irrigation (uROM), while
Fig. 4. Temporal distribution of (a) WSIw based on the ratio between water withdrawals/water availability, (b) WSIc based on the ratio between upstream water consumption/ water availability. Mean for the 1990–2006 period.
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Fig. 5. Spatial disaggregation of the main sectors involved in (a) water withdrawals and (b) consumptive use as well as (c, d) associated water scarcity. Mean for the 1990– 2006 period.
Bulgaria’s downstream water requirements are mainly for electricity generation and municipalities (dBGR). The same logic applies for all possible pairs of countries and for every month of the year. Note that the pies in Fig. 7 are not to-scale according to the quantities involved. Some pies represent values as low as 0.3 106 m3 year1, whereas others are as high as 20,775 106 m3 year1. Table 1 summarizes the 10 most important interrelations among all pairs of countries for all sub-basins and for sub-basins with high annual water scarcity. At the catchment scale, water consumptive use deprives 57% of the total quantity solely for users within the country in which it originates. Water withdrawals are also largely dependent on water resources yielded within the same country, for 63% of the total quantity. This is especially true in the coastal states of Turkey, Moldova, Russia, Ukraine, and Georgia, which have few interrelations with other countries in the catchment. In sub-basins with high water scarcity, more than 99% of the consumptive use and 94% of the demand are confined within the borders of the country in which they originate. 4. Discussion Modeling shows strong variation in seasonal water availability. This can result in periods of scarcity, meaning less water for the same number of dependent sectors, potentially leading to competition and conflicts. Our analysis indicates the potential for reinforcement of such intersectoral rivalries due to strong inequalities of water use and the predominance of essential
sectors, such as irrigation, in specific locations and during specific periods of the year. Our contribution highlights the intricate interdependence between human consumptive uses and environmental flow requirements. It shows how the need to preserve ecosystems applies additional pressure and further competition in the summer during the driest periods of the year, which is also a peak period for irrigation. Interrelations in the water-ecosystem-energy-food nexus mainly occur at the national level. This is because, on average, sub-basins in a given country are mostly interconnected with subbasins of the same country. Interrelations between different countries are larger, but they occur in fewer rivers. Consequently, even if the upstream drained area is large, interrelations exist through a narrower path in the downstream countries, impacting fewer downstream users. In addition, large rivers have higher water volumes that are able to dilute the effects of upstream consumption and exhibit no or low water scarcity. This explains why the vast majority of interrelations in scarcity prone sub-basins are intra-national. The spatial distribution of political borders and topography may serve as an explanation for this situation as well. Nevertheless, large channels can potentially connect and serve larger regions as water is pumped and redirected to fill the needs of nearby water scarce areas. These water diversions are not taken into account in this study. These results are thus scale dependent, and they would change if data were aggregated at different administrative divisions or for larger sub-basins, for example. In addition, the lack of seasonal data for power plants is a major limitation to the interpretation of the monthly results.
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Fig. 6. Relations among adjacent countries in terms of (a) water consumptive use and (b) requirements, both in 106 m3 year1.
The co-occurrence of these factors requires coordination between private users and public authorities. This is especially true for ecosystem services a key sector, common to all users that may suffer from negative externalities as a consequence of other activities. We assumed environmental flow requirements to
be nonnegotiable in this study. However, states can voluntarily choose to accept some degree of environmental deterioration to guarantee other socioeconomic benefits. The environmental flow requirement estimation provides a scientific basis for preserving essential ecosystem structures and functions. However, these
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Fig. 7. Sectors involved in (a) consumptive use and (b) withdrawals in upstream-downstream interrelations among countries. Pies not scaled according to quantities.
Table 1 Most important interrelations for “all” sub-basins and sub-basins with “high” water scarcity (WSIw 0.4 or WSIc 0.3); D = municipalities; P = power plants; M = manufacturing; I = irrigation; L = livestock; R = reservoirs. Users involved for more than 10% of quantities are in bold. WSI
Upstream Downstream country Amount involved [106 m3 year1] Upstream user consumptive use [% of country amount involved]
Ukraine Russia Turkey Romania Hungary Serbia Moldova Austria Russia Croatia ... High Ukraine Russia Turkey Romania Hungary Moldova Serbia Bulgaria Austria Slovakia All
Ukraine Russia Turkey Romania Hungary Serbia Moldova Austria Ukraine Serbia ... Ukraine Russia Turkey Romania Hungary Moldova Serbia Bulgaria Austria Hungary
31.8 24.1 17.8 7.5 4.8 4.7 4.6 3.8 3.6 3.2 20.5 11.8 11.1 4.3 3.7 3.4 3.2 2.2 1.9 1.5
Downstream users withdrawals [% of amount involved]
D
P
M
I
L
R
D
P
M
I
L
1.3 0.8 0.7 1.6 1.3 1.3 0.5 1.6 1.3 1.2 0.9 0.4 0.5 0.8 0.4 0.4 0.1 0.3 0.6 0.1
0.2 0.2 0.1 0.2 0.5 0.4 0.0 0.3 0.4 0.0 0.2 0.2 0.0 0.1 0.5 0.0 0.0 0.2 0.1 0.0
1.0 1.4 0.2 1.0 0.2 0.2 0.9 4.2 2.1 0.1 0.8 0.9 0.2 0.6 0.1 0.7 0.0 0.1 2.4 0.0
14.6 22.2 36.9 18.9 6.6 5.6 33.1 1.4 13.6 0.2 12.6 17.9 25.8 16.4 2.4 23.4 0.2 0.4 0.3 0.6
0.1 0.1 0.1 0.3 0.2 0.2 0.0 0.3 0.2 0.1 0.0 0.0 0.0 0.1 0.0 0.0 0.0 0.0 0.0 0.0
17.4 10.9 2.9 6.6 2.7 2.5 1.5 1.1 1.1 1.0 1.5 1.7 0.3 0.2 0.2 0.2 0.0 0.0 0.0 0.0
13.8 8.3 7.1 16.2 13.2 12.6 5.4 16.3 19.2 1.8 15.2 7.3 6.7 11.5 7.2 5.9 2.5 6.0 10.2 1.1
21.9 13.6 3.1 19.0 63.8 67.0 8.1 29.3 36.0 94.3 33.7 24.9 4.8 31.7 82.0 10.9 95.0 89.7 46.9 96.7
10.4 14.1 2.0 10.2 1.9 2.1 8.6 41.7 17.7 0.5 13.5 16.0 0.2 8.5 1.5 10.3 0.7 2.1 38.3 0.2
18.7 27.8 46.5 24.0 8.3 7.0 41.4 1.7 8.3 0.6 21.4 30.4 58.9 29.4 5.2 47.9 1.2 1.1 0.8 1.3
0.6 0.6 0.5 2.0 1.2 1.3 0.3 2.1 0.2 0.1 0.3 0.3 0.4 0.8 0.4 0.3 0.2 0.1 0.4 0.1
requirements will be the object of negotiations from the perspective of multiple sectors that are dependent on water resources. Determining a win-win situation between conservation and consumption represents a challenging task. It illustrates the growing need for a better understanding of the system through producing and accessing relevant data.
This also raises the question of the scale at which to consider these inter-sectoral trade-offs and the relevant framework to ensure inter-sectoral coordination (Pahl-Wostl, 2009). The WaterEcosystem-Energy-Food Nexus is materialized from the local to the transboundary level, implying the involvement of multiple regulatory frameworks and types of users. If the river basin tends to be recognized as a relevant indicator from a hydrological and
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normative point of view (Molle, 2009), the implementation of river management measures depends on actions implemented at the national level. In this regard, the role of international organizations, such as the International Commission for the Protection of the Danube River (ICPDR) and the Black Sea Commission (BSC), is key for ensuring inter-sectoral coordination at different levels, for defining shared action plans to be adopted by state members, and for framing the represented and defended sectors of activity. 5. Conclusions A water-ecosystem-energy-food nexus approach in the Black Sea catchment should focus on water scarcity that occurs in the summer due to the higher demand for irrigation and reservoirs in conjunction with the relatively lower water resources; additionally, water scarcity in the fall-winter period due to the lower water resources and relatively high demand for preserving ecosystems and sectors other than irrigation should be considered. Turkey, Moldova, Ukraine, Russia, Romania, and Hungary are particularly affected. The spatial distribution of the rivers and national borders leads upstream-downstream interrelations among users in water scarce sub-basins to occur mainly at the national level, with an emphasis on water management by national governments as essential in mitigating water scarcity within the catchment. However, results also show many interrelations among different countries, especially in the Danube river basin, as well as between Russia and Ukraine, stressing the need for international cooperation. Our results illustrate the necessity to increase the understanding of existing inter-sectoral linkages and the functioning of the value-chain at the transboundary level (Schmeier, 2014). This calls for an in-depth analysis of the involved sectors of activity. Future research should focus on the understanding of usage modalities, the identification and quantification of different intakes, and the identification of trade-offs and possible synergies among the sectors involved in the water-ecosystem-energy-food nexus. It should also focus on the different governance frameworks, their capacity to frame negotiations and resolve power struggles among different companies to ensure the preservation of ecosystems. In this study, the water-ecosystem-energy-food nexus approach offers a relevant perspective to study resource allocations and possible trade-offs among sectors. Nevertheless, our study, in particular, shows that this understanding will depend on better access to data at different levels (Hayes and Crilly, 2014), and regard for regional, national, and transboundary frameworks (de Strasser et al., 2016). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j. envsci.2016.09.004. References Arnold, J.G., Moriasi, D.N., Gassman, P.W., Abbaspour, K.C., White, M.J., Srinivasan, R., Jha, M.K., 2012. SWAT: model use, calibration, and validation. Trans. Asabe 55 (4), 1491–1508. Baer, R., Rouholahnedjad, E., Rahman, K., Abbaspour, K.C., Lehmann, A., 2015. Climate change and agricultural water resources: a vulnerability assessment of the Black Sea catchment. Environ. Sci. Policy 46, 57–69. Bazilian, M., Rogner, H., Howells, M., Hermann, S., Arent, D., Gielen, D., Yumkella, K. K., 2011. Considering the energy, water and food nexus: towards an integrated modelling approach. Energy Policy 39 (12), 7896–7906. CIESIN, 2011. Global Rural-Urban Mapping Project (GRUMP). . Chapagain, A.K., Hoekstra, A.Y., 2003. Virtual Water Flows Between Nations in Relation to Trade in Livestock and Livestock Products. .
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Environmental Science & Policy journal homepage: www.elsevier.com/locate/envsci
Blue water scarcity in the Black Sea catchment: Identifying key actors in the water-ecosystem-energy-food nexus M. Fasela,* , C. Bréthauta , E. Rouholahnejadb , M.A. Lacayo-Emerya , A. Lehmanna a b
University of Geneva, Institute for Environmental Sciences, Bd. Carl-Vogt 66, CH – 1211, Geneva, Switzerland Department of Environmental Systems Science, ETH Zurich, Universitaetstrasse 16, CH – 8092, Zurich, Switzerland
A R T I C L E I N F O
Article history: Received 18 February 2016 Received in revised form 2 August 2016 Accepted 10 September 2016 Available online xxx Keywords: Water Scarcity Nexus Ecosystems Energy Food
A B S T R A C T
Large-scale water scarcity indicators have been widely used to map and inform decision makers and the public about the use of river flows, a vital and limited renewable resource. However, spatiotemporal interrelations among users and administrative entities are still lacking in most large-scale studies. Water scarcity and interrelations are at the core of the water-ecosystem-energy-food nexus. In this paper, we balance water availability in the Black Sea catchment with requirements and consumptive use of key water users, i.e., municipalities, power plants, manufacturing, irrigation and livestock breeding, accounting for evaporation from major reservoirs as well as environmental flow requirements. We use graph theory to highlight interrelations between users and countries along the hydrological network. The results show that water scarcity occurs mainly in the summer due to higher demand for irrigation and reservoir evaporation in conjunction with relatively lower water resources, and in the fall-winter period due to lower water resources and the relatively high demand for preserving ecosystems and from sectors other than irrigation. Cooling power plants and the demands of urban areas cause scarcity in many isolated locations in the winter and, to a far greater spatial extent, in the summer with the demands for irrigation. Interrelations in water scarcity-prone areas are mainly between relatively small, intra-national rivers, for which the underlying national and regional governments act as key players in mitigating water scarcity within the catchment. However, many interrelations exist for larger rivers, highlighting the need for international cooperation that could be achieved through a water-ecosystem-energy-food nexus. ã 2016 Elsevier Ltd. All rights reserved.
1. Introduction Water scarcity is a growing concern in many parts of the world as it leads to conflicts, overexploitation of aquifers, increased pollution, alteration of ecosystems, and various negative effects on human health, food and goods production, and economic wellbeing (Jury and Vaux, 2007; Kummu et al., 2010). Water scarcity is both a natural and anthropogenic phenomenon (Jaeger et al., 2013). It can be caused not only by unfavorable climate changes and the failure of a society to adapt but also by excessive and increasing water demand vital to sustaining population growth, industry and agriculture. Moreover, water infrastructure can change the temporal pattern of streamflow, and
* Corresponding author. E-mail address: [email protected] (M. Fasel). http://dx.doi.org/10.1016/j.envsci.2016.09.004 1462-9011/ã 2016 Elsevier Ltd. All rights reserved.
human activities that consume water through evaporation or incorporation into products eventually deplete a significant amount of resources from the hydrological system (Hoekstra et al., 2012). There has been a growing recognition that ecosystems are a central and legally established water user, and in 1982, the World Charter for Nature imposed further reductions to water use in nation states committed to their protection. Consequently, competition for available resources is likely to increase (FAO, 2012). This raises the need to decrease water demand, improve the efficiency of water consumption, and lessen the impacts of consumptive use and streamflow regulations to ensure a balance between socioeconomic development and environmental protection (Hamdy et al., 2003). At the Bonn 2011 Nexus Conference, the concept of a water nexus, which allows for causal links between users and their common resources in water management plans (Hoff, 2011), was
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identified as an innovative way to mitigate water scarcity. The purpose of this approach is to encourage cooperation, reduce trade-offs, and improve consumption efficiency and cross-sectorial policy coherence so that undesirable effects from water use or climate change can be reduced (Bazilian et al., 2011). To this aim, evaluating nexus structures and dynamics in a geographical area allows for the prediction of potential conflicts or opportunities for synergy among users (Wolf, 2007). The Black Sea catchment suffers from water scarcity in many areas and is subject to a complex set of interrelations involving 23 countries, many different types of users, and four important international river basins. The need for improving ecological conditions and managing growing conflicts of interest in the area (GIWA, 2011) requires regional coordination by the existing national and international institutional framework, including the Black Sea Commission and the International Commission for the Protection of the Danube River (Myroshnychenko et al., 2015). Indeed, water scarcity can be a trigger for cooperation among countries instead of a source of conflict, primarily in situations where institutional frameworks exist (Gizelis and Wooden, 2010) and if scarcity is not extreme, but moderate (Dinar, 2009). A few global and regional studies have assessed water availability, use and scarcity in the catchment (Baer et al., 2015; Floerke et al., 2012; Hoekstra et al., 2012; Karabulut et al., 2015; Lehmann et al., 2015). Although some of these reports localize users, none have examined upstream-downstream interrelations in detail. Interrelations are at the core of the nexus concept. In this paper, we identify interrelations along the hydrological network using graph theory (Gould, 2012). We focus on so-called surface “blue water” (Falkenmark and Rockstrom, 2006) that is available in rivers. We intend to answer the following questions:
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As a transnational entity, the catchment covers parts of 23 countries1, and is inhabited by more than 180 million people (UNEP, 2013; World Bank, 2015). Municipalities, industries, and agriculture are all major water users, depending on region (FAO, 2013), and ecosystems preservation has been legally recognized in all countries (Paleari et al., 2005). The catchment is subject to various international water treaties and policies. The major international agreements are established by the Black Sea Commission (BSC) in the coastal states, the International Commission for the Protection of the Danube River (ICPDR) in the Danube river basin, and the Water Framework Directive (WFD) in the European Union and candidate countries (Paleari et al., 2005). The catchment was the focus of European research project enviroGRIDS (Lehmann et al., 2015) between the years 2009 and 2013, which aimed at building the capacity for this region to use and share earth observation data to support sustainable development (Giuliani et al., 2013). The present work builds on the outcomes of this project, primarily the hydrological model for the entire Black Sea catchment realized at sub-basin and daily temporal resolution (Rouholahnejad et al., 2014). 2.2. Frameworks of analysis
2. Methods
This work was accomplished in several consecutive steps, linked as in Fig. 2. (1) First, we assessed river flows (RF) with the Soil and Water Assessment Tool (SWAT) (Rouholahnejad et al., 2014). (2) Then, we estimated water withdrawals (WW) and consumptive use (WC) for municipalities, power plants, manufacturing, irrigation, and livestock breeding. (3) Adding WC to RF, we estimated the naturalized river flow (NRF). NRF is then used to assess environmental flow requirements (EFR), i.e., the part of flow necessary for preserving critical ecosystem structures and functions. The remaining NRF after allocation of EFR is the quantity of water available (WA) for human use without harming the environment. (4) We then allocate water consumptive use (WC), i.e., the evaporation or incorporation into products of human activities. Next, we compare water withdrawals (WW) of human activities with the remaining available water to identify sub-basins and periods of water scarcity through water scarcity indices (WSI). (5) We identify upstream-downstream interrelations among users and countries using surface water as an entry point for defining nexus structures in the Black Sea catchment on the ground as it is a common resource to all users. We subdivided the Black Sea catchment into the 23 national territories mentioned previously, nine main river basins2 and 12,982 sub-basins of 100 km2, the latter having been defined by hydrological modeling (Rouholahnejad et al., 2014). These subbasins were the smallest units of analysis and were subsequently aggregated into river basins, national territories, or catchments when required (Fig. 3). As water availability and requirements vary widely throughout the year, we used a monthly time scale to take into account these variations.
2.1. Study area
2.3. Water availability
The Black Sea catchment is situated in the Northern hemisphere at the interface between Europe and western Asia. It covers an area of approximately 2.4 million km2 and includes four important transboundary river basins: the Danube, the Dnieper, the Dniester, and the Don (Fig. 1). The catchment is home to a large variety of topographic and climatic conditions ranging from temperate and alpine areas in the west, continental and steppe regions in the north and the east, and Mediterranean and semi-arid areas in the south.
Rouholahnejad et al. (2014) modeled blue and green water availability with the Soil and Water Assessment Tool (SWAT)
Where and when is water scarcity most likely to occur in the Black Sea catchment? What countries and users are involved in these water scarce areas and what are their upstream-downstream interrelations? How can such analysis be employed in a nexus framework to mitigate water scarcity in the Black Sea catchment? To answer these questions, we spatiotemporally balanced water availability with environmental flow requirements, as well as water withdrawals and consumptive use by the main types of water users, specifically municipalities, energy, manufacturing, irrigation, and livestock breeding while taking into account evaporation from major reservoirs. Then, we identify existing upstream-downstream interrelations among countries and types of users using a directed acyclic graph (DAG) (Gould, 2012) of the river network. The users and countries identified as key players should be given priority to mitigate water scarcity in the catchment by implementing a nexus regulatory framework.
1 Albania, Austria, Belarus, Bosnia and Herzegovina, Bulgaria, Croatia, Czech Republic, Georgia, Germany, Hungary, Italia, Macedonia, Moldova, Montenegro, Poland, Romania, Russia, Serbia (incl. Kosovo), Slovakia, Slovenia, Switzerland, Turkey, Ukraine 2 Danube, Dnieper, Dniester, Don, Kelkit, Kizil, Kuban, Rioni, Southern Bug
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Fig. 1. Map of the Black Sea catchment: (a) general location and (b) main geographical features.
(Arnold et al., 2012) at the sub-basin spatial scale and with daily temporal resolution for the entire catchment. In the present study, surface water availability was defined as river flow, which is formed by accumulation along the hydrological system of the subbasin water yield. Water yield is the net amount of water that is equivalent to surface runoff, lateral flows, and groundwater from shallow aquifers contributing to streamflow minus losses through the streambed and evaporation. Monthly averages of river flows for the period of 1990–2006 were obtained from this model and used for analysis. The model takes into account the spatial and temporal dynamics of land use and was intended to represent water-related processes in their natural state. Dam and reservoir management as well as water diversion data were usually not available in most of the catchment and were not included in the hydrological modeling. We also assumed that the model implicitly accounted for water consumption as it was calibrated against recorded gauge observations. Accordingly, the naturalized river flow, i.e., the flow that would exist without human consumptive use (Doell et al., 2009; Haddeland et al., 2014), was approximated by adding water consumptive use to the modeled flow. 2.4. Water needs and consumptive use 2.4.1. Environmental flow requirements The river flow regime, which involves the flow magnitude, frequency, duration, timing, and predictability, is the principal force that determines many fundamental natural ecological characteristics of river ecosystems extreme events, low and high-flow seasons that shape habitats, species distributions, and
ecosystem functioning (Lytle and Poff, 2004; Poff and Zimmerman, 2010). Consequently, establishing river flows within a range that maintains beneficial ecological status is of prime importance to preserve stream and riparian flora and fauna. To assess this quantity, we used the “Variable Monthly Flow (VMF)” method (Pastor et al., 2014), assuming a “fair” level of protection policy to determine monthly environmental flow requirements (EFR) in relation to monthly natural flow variability. A “fair” level of protection policy allows for multiple disturbances to occur so that socioeconomic development can be supported and is the lowest level of acceptable protection from a water management perspective (Smakhtin et al., 2004). Low, intermediate and high-flow seasons were defined by classifying months into groups with a mean flow under 40%, between 40%–80% or above 80% of the mean annual flow, respectively. As relatively more water is required for ecosystems during low-flow periods compared to high-flow periods, flow reserved for ecosystems was fixed at 60% during low-flow, 30–60% during intermediate-flow, and 30% during high-flow seasons, hence allocating 40, 40–70, and 70% of the monthly mean flow for other uses, respectively (Pastor et al., 2014). Like (Richter et al., 2012), these percentages of water allocated for the environment can be observed as a default protection policy, as more detailed, sound assessments have not yet been conducted for any particular river. 2.4.2. Sectorial withdrawals and consumptive use The methods employed to estimate withdrawals by sectors were derived from other studies (Floerke and Alcamo, 2005; Floerke et al., 2013). Consumption was defined as the ratio of withdrawn quantities not returning to the environment after use
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Fig. 2. Conceptual framework for the analysis of the nexus structure in the Black Sea catchment.
either by evaporation or incorporation into products, therefore unavailable for reuse downstream. The time series were obtained from FAO, UNICEF, World Bank, state statistical office databases, and the literature for the period of 1990–circa 2014 (Supplemental Information, Appendix A and B for more detail on data and calculations). The withdrawals by municipalities were calculated using urban and rural population densities (CIESIN, 2011), rates of connection to running water supply systems (WHO and UNICEF, 2013), and national domestic water withdrawal intensities. Water consumption was assumed to be 10% of this quantity (Hoekstra et al., 2012). Withdrawals and consumptive use for cooling power plants were calculated with consideration of electricity generation, fuel type3 , and the cooling systems4 of 3604 plants (Davis et al., 2012; GEO, 2014). Water withdrawal and consumption intensities for each combination of fuel type and cooling system were obtained from the literature (Davies et al., 2013; Macknick et al., 2012). The water requirements for manufacturing were acquired from national statistics and downscaled according to urban population density.
3 Nuclear, coal, gas, combined-cycle, oil, biogas, biomass, geothermal, solar, waste, wind, and hydropower. 4 Once-through or closed-loop cooling, including tower or ponds when available. 5 Wheat, maize, rice, barley, rye, millet, soybeans, sunflower, potatoes, sugar beet, rape seed/canola, groundnuts/peanuts, pulses, citrus, grapes/vine, cotton, others perennial, fodder grasses, and other annuals.
Water consumption for this sector was assumed to be 10% of withdrawals (EC, 2014). Net irrigation water requirements for 19 types of crops5 present in the catchment were obtained from Siebert and Doell (2008) and temporally allocated using the same crop coefficient method as in aus der Beek et al. (2012) using a daily Penman-Monteith equation. A country-specific irrigation efficiency factor (aus der Beek et al., 2010; Rohwer et al., 2007) was applied to obtain gross irrigation withdrawals. A consumptive use of 80% was assumed (Nixon et al., 2003). Withdrawals for livestock breeding were estimated using cattle, goat, sheep, pig, and poultry densities (FAO, 2013; Robinson et al., 2014), as well as dominant livestock production systems (Robinson et al., 2011). Withdrawal intensities for each combination of breeding and production systems were derived from Chapagain and Hoekstra (2003) with an assumed consumptive use of 15% (De Roo et al., 2012). In the absence of monthly data, withdrawals and consumption for all sectors, except for irrigation, were assumed to remain constant during the year and to vary only interannually. Irrigation is highly seasonal in the catchment, as described in section 3.1. Improvements have yet to be made for modeling the seasonality for other users, notably power plants. Evaporation from the 238 large reservoirs listed in Lehner et al. (2011), supplemented by 87 additional reservoirs in the ECRINS (EEA, 2012) and GeoNames (GeoNames, 2015) databases, was estimated assuming a daily evaporation that is 10% higher than the reference evapotranspiration throughout the entire year
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Fig. 3. Map of the hydrological network used for the analysis. It comprises nine main river basins and 12,982 reaches, representing each sub-basin with an area 100 km2.
(Hoogeveen et al., 2015). Daily reference evapotranspiration was computed by the SWAT model using the Penman-Monteith equation. We assumed that the effects of water consumption within a month are limited to that month.
The following representative scale was then used: WSIc <0.2: No scarcity; 0.2–0.3: Low; 0.3–0.4: High; >0.4: Very high. Blue water scarcity using the demand index was estimated using the quotient of total withdrawals by surface water available for human use (Smakhtin et al., 2004):
2.5. Water scarcity
WSIw ¼
We used two complementary scarcity indices in this study. The first is focused on consumption and how its reduction of water flow can threaten downstream ecosystems and users. The second addresses demand, i.e., withdrawals, and how water availability can be insufficient even independently of upstream consumptive use. Blue water scarcity using the consumptive index was estimated from the quotient of upstream consumptive use divided by surface water available for human use (Hoekstra et al., 2012):
where WSIw is the water demand scarcity index [] and WW is the water withdrawals in m3 month1. The following representative scale was then used: WSIw <0.1: No scarcity; 0.1–0.2: Low; 0.2–0.4: Moderate; 0.4–0.8: High; >0.8: Very high.
WSIc ¼
UWC UWC ¼ WA NFR EFR UWC
ð1Þ
where WSIc is the consumptive use scarcity index [], UWC is the total water consumption in upstream sub-basins, WA is the water available without harming ecosystems, NRF is the naturalized river flow, and EFR is the environmental flow requirements, with all variables in m3 month1 except for WSIc, which is dimensionless.
WW WW ¼ WA NRF EFR UWC
ð2Þ
2.6. Upstream-downstream interrelations Interrelations were analyzed using a directed acyclic graph (DAG) of the hydrological network built in R with the igraph package (Csardi and Nepusz, 2006), integrating the above results. Sub-basins and reaches were defined as vertices and edges of the graph, respectively. To determine interrelations, all of the sub-basins of each country were selected, and for each sub-basin in a given country, we searched for the main upstream impacting sectors and countries as well as the main downstream inquiring sectors and countries.
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For interrelations in water scarce sub-basins, we only selected sub-basins with a high water scarcity index, i.e., WSIw 0.4 or WSIc 0.3. Two matrices, one for consumptive use and one for withdrawals, were filled during this process to gather the results between each possible pair of countries. Interrelations were computed solely based on water quantity consumed and withdrawn. We considered interrelations to be bidirectional. Indeed, upstream users impact downstream users through consumptive use, while downstream users can also impose constraints on water allowed to be depleted upstream through cooperative agreements. We represent these interrelations between countries using diagrams that emphasize bilateral relations. The diagrams must be interpreted from a cooperative perspective, showing that both upstream consumptive use and downstream water needs should be reduced to mitigate water scarcity. 3. Results 3.1. Spatiotemporal representation of water scarcity Most of the estimated 467 billion m3 year1 of surface water is available during the spring, when there is approximately twice as much water as the rest of the year, less abundant periods being the end of summer and middle of winter (Fig. 4a and b). The Danube basin represents about 50% of all annual available water, the Dnieper 16%, the Don 10% the Kuban 4.6%, and the Dniester 2%, with 17.4% in other river basins with no one having more than 2%. On average, naturalized flow was 5% higher than modeled river flow, representing 495 billion m3 year1 (Supplemental Information, Appendix C). Approximately 40% of this water, i.e., 209 billion m3 year1, had to be reserved for freshwater ecosystem preservation, allowing 258 billion m3 year1 for other uses. On this amount, human activity sectors withdraw an estimated 77 billion m3 year1, with industry as the largest user at 45% (30% for cooling power plants and 15% for manufacturing). Other uses included 35% for irrigation, 19% for municipalities (12% for urban areas and 7% for rural regions), and 1% for livestock breeding. Consumptive use was estimated to reach 32 billion m3 year1, with 58% used for irrigation, 32% by reservoirs evaporation, 4.8% used in municipalities, 2.2% used for livestock breeding, 1.7% used in manufacturing, and 1.3% used for power plants. Irrigation shows a strong seasonal pattern as most irrigated crops start growing in May and continue to grow while increasing
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their water needs until harvest season in August or September. Similarly, reservoir evaporation is the highest during this same period. Therefore, water withdrawals and consumption are almost entirely from other sectors during most of the year, with irrigation and reservoir evaporation adding their effects mostly during the summertime (Fig. 4a and b). As a result of these temporal shifts between water availability and use, there are two major periods where water scarcity is high: 1) the summer, due to the higher demand from irrigation, consumptive use from irrigation and reservoirs, and reduced water resources, while demand from other sectors remains constant; and 2) the fall-winter period, due to reduced water resources and a higher demand for ecosystem preservation and sectors other than irrigation (Fig. 4a and b). This seasonal pattern is generally true for all river basins within the catchment, although it varies in amplitude and length, leading to water scarcity in different areas with varying degrees of severity and duration that affect many users. Indeed, further spatial disaggregation shows that the spatiotemporal distribution of major water users, as well as scarcity, varies considerably among regions on an annual (Fig. 5) and monthly (Supplemental Information, Appendix E and G) basis. In particular, cooling power plants and the demands of urban areas cause scarcity in many isolated locations in winter and, to a far greater spatial extent, in the summer with the demands of irrigation (Appendix E). 3.2. Upstream-downstream interrelations Graph analysis shows that there are many mutual interrelations between countries. The hydrography and national border configurations are such that two countries can be upstream and downstream to each other simultaneously. These intricacies must be analyzed at the sub-basin scale to be detected. Often, though, these relations are asymmetric in terms of quantity, meaning that one country can outweigh the other regarding consumptive use and requirements (Fig. 6a and b). Disaggregating Fig. 6, interrelations among all possible users and pairs of countries can be summarized as in Fig. 7. As an example, we can determine interrelations between Bulgaria and Romania: Bulgaria consumes water upstream mainly through reservoir evaporation, irrigation, and municipalities (uBGR), whereas Romania’s downstream water requirements are mostly for electricity generation (dROM). In addition, Romania consumes water upstream mainly from reservoirs and irrigation (uROM), while
Fig. 4. Temporal distribution of (a) WSIw based on the ratio between water withdrawals/water availability, (b) WSIc based on the ratio between upstream water consumption/ water availability. Mean for the 1990–2006 period.
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Fig. 5. Spatial disaggregation of the main sectors involved in (a) water withdrawals and (b) consumptive use as well as (c, d) associated water scarcity. Mean for the 1990– 2006 period.
Bulgaria’s downstream water requirements are mainly for electricity generation and municipalities (dBGR). The same logic applies for all possible pairs of countries and for every month of the year. Note that the pies in Fig. 7 are not to-scale according to the quantities involved. Some pies represent values as low as 0.3 106 m3 year1, whereas others are as high as 20,775 106 m3 year1. Table 1 summarizes the 10 most important interrelations among all pairs of countries for all sub-basins and for sub-basins with high annual water scarcity. At the catchment scale, water consumptive use deprives 57% of the total quantity solely for users within the country in which it originates. Water withdrawals are also largely dependent on water resources yielded within the same country, for 63% of the total quantity. This is especially true in the coastal states of Turkey, Moldova, Russia, Ukraine, and Georgia, which have few interrelations with other countries in the catchment. In sub-basins with high water scarcity, more than 99% of the consumptive use and 94% of the demand are confined within the borders of the country in which they originate. 4. Discussion Modeling shows strong variation in seasonal water availability. This can result in periods of scarcity, meaning less water for the same number of dependent sectors, potentially leading to competition and conflicts. Our analysis indicates the potential for reinforcement of such intersectoral rivalries due to strong inequalities of water use and the predominance of essential
sectors, such as irrigation, in specific locations and during specific periods of the year. Our contribution highlights the intricate interdependence between human consumptive uses and environmental flow requirements. It shows how the need to preserve ecosystems applies additional pressure and further competition in the summer during the driest periods of the year, which is also a peak period for irrigation. Interrelations in the water-ecosystem-energy-food nexus mainly occur at the national level. This is because, on average, sub-basins in a given country are mostly interconnected with subbasins of the same country. Interrelations between different countries are larger, but they occur in fewer rivers. Consequently, even if the upstream drained area is large, interrelations exist through a narrower path in the downstream countries, impacting fewer downstream users. In addition, large rivers have higher water volumes that are able to dilute the effects of upstream consumption and exhibit no or low water scarcity. This explains why the vast majority of interrelations in scarcity prone sub-basins are intra-national. The spatial distribution of political borders and topography may serve as an explanation for this situation as well. Nevertheless, large channels can potentially connect and serve larger regions as water is pumped and redirected to fill the needs of nearby water scarce areas. These water diversions are not taken into account in this study. These results are thus scale dependent, and they would change if data were aggregated at different administrative divisions or for larger sub-basins, for example. In addition, the lack of seasonal data for power plants is a major limitation to the interpretation of the monthly results.
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Fig. 6. Relations among adjacent countries in terms of (a) water consumptive use and (b) requirements, both in 106 m3 year1.
The co-occurrence of these factors requires coordination between private users and public authorities. This is especially true for ecosystem services a key sector, common to all users that may suffer from negative externalities as a consequence of other activities. We assumed environmental flow requirements to
be nonnegotiable in this study. However, states can voluntarily choose to accept some degree of environmental deterioration to guarantee other socioeconomic benefits. The environmental flow requirement estimation provides a scientific basis for preserving essential ecosystem structures and functions. However, these
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Fig. 7. Sectors involved in (a) consumptive use and (b) withdrawals in upstream-downstream interrelations among countries. Pies not scaled according to quantities.
Table 1 Most important interrelations for “all” sub-basins and sub-basins with “high” water scarcity (WSIw 0.4 or WSIc 0.3); D = municipalities; P = power plants; M = manufacturing; I = irrigation; L = livestock; R = reservoirs. Users involved for more than 10% of quantities are in bold. WSI
Upstream Downstream country Amount involved [106 m3 year1] Upstream user consumptive use [% of country amount involved]
Ukraine Russia Turkey Romania Hungary Serbia Moldova Austria Russia Croatia ... High Ukraine Russia Turkey Romania Hungary Moldova Serbia Bulgaria Austria Slovakia All
Ukraine Russia Turkey Romania Hungary Serbia Moldova Austria Ukraine Serbia ... Ukraine Russia Turkey Romania Hungary Moldova Serbia Bulgaria Austria Hungary
31.8 24.1 17.8 7.5 4.8 4.7 4.6 3.8 3.6 3.2 20.5 11.8 11.1 4.3 3.7 3.4 3.2 2.2 1.9 1.5
Downstream users withdrawals [% of amount involved]
D
P
M
I
L
R
D
P
M
I
L
1.3 0.8 0.7 1.6 1.3 1.3 0.5 1.6 1.3 1.2 0.9 0.4 0.5 0.8 0.4 0.4 0.1 0.3 0.6 0.1
0.2 0.2 0.1 0.2 0.5 0.4 0.0 0.3 0.4 0.0 0.2 0.2 0.0 0.1 0.5 0.0 0.0 0.2 0.1 0.0
1.0 1.4 0.2 1.0 0.2 0.2 0.9 4.2 2.1 0.1 0.8 0.9 0.2 0.6 0.1 0.7 0.0 0.1 2.4 0.0
14.6 22.2 36.9 18.9 6.6 5.6 33.1 1.4 13.6 0.2 12.6 17.9 25.8 16.4 2.4 23.4 0.2 0.4 0.3 0.6
0.1 0.1 0.1 0.3 0.2 0.2 0.0 0.3 0.2 0.1 0.0 0.0 0.0 0.1 0.0 0.0 0.0 0.0 0.0 0.0
17.4 10.9 2.9 6.6 2.7 2.5 1.5 1.1 1.1 1.0 1.5 1.7 0.3 0.2 0.2 0.2 0.0 0.0 0.0 0.0
13.8 8.3 7.1 16.2 13.2 12.6 5.4 16.3 19.2 1.8 15.2 7.3 6.7 11.5 7.2 5.9 2.5 6.0 10.2 1.1
21.9 13.6 3.1 19.0 63.8 67.0 8.1 29.3 36.0 94.3 33.7 24.9 4.8 31.7 82.0 10.9 95.0 89.7 46.9 96.7
10.4 14.1 2.0 10.2 1.9 2.1 8.6 41.7 17.7 0.5 13.5 16.0 0.2 8.5 1.5 10.3 0.7 2.1 38.3 0.2
18.7 27.8 46.5 24.0 8.3 7.0 41.4 1.7 8.3 0.6 21.4 30.4 58.9 29.4 5.2 47.9 1.2 1.1 0.8 1.3
0.6 0.6 0.5 2.0 1.2 1.3 0.3 2.1 0.2 0.1 0.3 0.3 0.4 0.8 0.4 0.3 0.2 0.1 0.4 0.1
requirements will be the object of negotiations from the perspective of multiple sectors that are dependent on water resources. Determining a win-win situation between conservation and consumption represents a challenging task. It illustrates the growing need for a better understanding of the system through producing and accessing relevant data.
This also raises the question of the scale at which to consider these inter-sectoral trade-offs and the relevant framework to ensure inter-sectoral coordination (Pahl-Wostl, 2009). The WaterEcosystem-Energy-Food Nexus is materialized from the local to the transboundary level, implying the involvement of multiple regulatory frameworks and types of users. If the river basin tends to be recognized as a relevant indicator from a hydrological and
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normative point of view (Molle, 2009), the implementation of river management measures depends on actions implemented at the national level. In this regard, the role of international organizations, such as the International Commission for the Protection of the Danube River (ICPDR) and the Black Sea Commission (BSC), is key for ensuring inter-sectoral coordination at different levels, for defining shared action plans to be adopted by state members, and for framing the represented and defended sectors of activity. 5. Conclusions A water-ecosystem-energy-food nexus approach in the Black Sea catchment should focus on water scarcity that occurs in the summer due to the higher demand for irrigation and reservoirs in conjunction with the relatively lower water resources; additionally, water scarcity in the fall-winter period due to the lower water resources and relatively high demand for preserving ecosystems and sectors other than irrigation should be considered. Turkey, Moldova, Ukraine, Russia, Romania, and Hungary are particularly affected. The spatial distribution of the rivers and national borders leads upstream-downstream interrelations among users in water scarce sub-basins to occur mainly at the national level, with an emphasis on water management by national governments as essential in mitigating water scarcity within the catchment. However, results also show many interrelations among different countries, especially in the Danube river basin, as well as between Russia and Ukraine, stressing the need for international cooperation. Our results illustrate the necessity to increase the understanding of existing inter-sectoral linkages and the functioning of the value-chain at the transboundary level (Schmeier, 2014). This calls for an in-depth analysis of the involved sectors of activity. Future research should focus on the understanding of usage modalities, the identification and quantification of different intakes, and the identification of trade-offs and possible synergies among the sectors involved in the water-ecosystem-energy-food nexus. It should also focus on the different governance frameworks, their capacity to frame negotiations and resolve power struggles among different companies to ensure the preservation of ecosystems. In this study, the water-ecosystem-energy-food nexus approach offers a relevant perspective to study resource allocations and possible trade-offs among sectors. Nevertheless, our study, in particular, shows that this understanding will depend on better access to data at different levels (Hayes and Crilly, 2014), and regard for regional, national, and transboundary frameworks (de Strasser et al., 2016). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j. envsci.2016.09.004. References Arnold, J.G., Moriasi, D.N., Gassman, P.W., Abbaspour, K.C., White, M.J., Srinivasan, R., Jha, M.K., 2012. SWAT: model use, calibration, and validation. Trans. Asabe 55 (4), 1491–1508. Baer, R., Rouholahnedjad, E., Rahman, K., Abbaspour, K.C., Lehmann, A., 2015. Climate change and agricultural water resources: a vulnerability assessment of the Black Sea catchment. Environ. Sci. Policy 46, 57–69. Bazilian, M., Rogner, H., Howells, M., Hermann, S., Arent, D., Gielen, D., Yumkella, K. K., 2011. Considering the energy, water and food nexus: towards an integrated modelling approach. Energy Policy 39 (12), 7896–7906. CIESIN, 2011. Global Rural-Urban Mapping Project (GRUMP). . Chapagain, A.K., Hoekstra, A.Y., 2003. Virtual Water Flows Between Nations in Relation to Trade in Livestock and Livestock Products. .
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