Countries sharing river basins are often dependent upon water originating outside their boundaries; meaning that without that upstream water, water scarcity may occur with flow-on implications for water use and management. We develop a formalisation of this concept drawing on ideas about the transition between regimes from resilience literature, using water stress and water shortage as indicators of water scarcity. In our analytical framework, dependency occurs if water from upstream is needed to avoid scarcity. This can be diagnosed by comparing different types of water availability on which a sub-basin relies, in particular local runoff and upstream inflows. At the same time, possible upstream water withdrawals reduce available water downstream, influencing the latter water availability. By developing a framework of scarcity and dependency, we contribute to the understanding of transitions between system regimes. We apply our analytical framework to global transboundary river basins at the scale of sub-basin areas (SBAs). Our results show that 1175 million people live under water stress (42 % of the total transboundary population). Surprisingly, the majority (1150 million) of these currently suffer from stress only due to their own excessive water use and possible water from upstream does not have impact on the stress status – i.e. they are not yet dependent on upstream water to avoid stress – but could still impact on the intensity of the stress. At the same time, 386 million people (14 %) live in SBAs that can avoid stress owing to available water from upstream and have thus upstream dependency. In the case of water shortage, 306 million people (11 %) live in SBAs dependent on upstream water to avoid possible shortage. The identification of transitions between system regimes sheds light on how SBAs may be affected in the future, potentially contributing to further refined analysis of inter- and intrabasin hydro-political power relations and strategic planning of management practices in transboundary basins.
While water is a renewable resource, its availability is finite. As population and water demand grow, water becomes scarce. If local precipitation is insufficient to meet needs, a region may draw on external water resources, both physical and virtual (through food and goods trade) (Hoekstra and Chapagain, 2011). External water resources constitute a considerable part of the total renewable water of some countries, and create hydrological, social, and economic interdependencies between countries (Hoekstra and Mekonnen, 2012). Transboundary water resources crossing national borders are a high-profile example. In basins like the Nile, water availability of the downstream countries (Sudan, Egypt) is highly dependent on upstream precipitation patterns and upstream water use (Drieschova et al., 2008). Transboundary river basins cover almost half of the earth's land surface, and are home to about one-third of the world's population (UN Water, 2013).
“Hydro-political dependency” in transboundary river basins is an important geopolitical issue bound up with concerns of sovereignty, and affects the power relations between riparian countries (Brochmann and Gleditsch, 2012; Giordano and Wolf, 2003; Gleick, 2014; Jägerskog and Zeitoun, 2009; Mirumachi, 2013, 2015; Wolf, 1998, 1999, 2007). An increase in water demand is among the main factors responsible for water scarcity in most transboundary river basins (Degefu et al., 2016). Uncontrolled land and water development in upstream regions can escalate risk of water supply uncertainty in the downstream region (Al-Faraj and Scholz, 2015; Drieschova et al., 2008; Veldkamp et al., 2017). Concerns about water availability are already considered to be one of the most important issues for international cooperation and conflict concerning shared water basins (Beck et al., 2014). Regional and global studies already show that upstream water use has a considerable impact on downstream water scarcity (Munia et al., 2016; Nepal et al., 2014; Scott et al., 2003; Veldkamp et al., 2017). When populations (or water withdrawals) grow, downstream countries eventually become more reliant on the water available from upstream parts of a basin in order to satisfy their needs.
In this study, we aim to explore one particular definition of “upstream dependency”. Intuitively, one could say that upstream water dependency occurs if water from upstream is needed to avoid water scarcity. Dependency therefore involves a sharp transition between cases where water scarcity is or is not experienced depending on whether water from upstream is or is not available. Transitions between cases is a key idea in resilience thinking, which therefore provides a promising way of approaching this problem.
“Resilience” of a socio-ecological system is defined as “the capacity of a
system to absorb disturbance and reorganise while undergoing change so as to
still retain essentially
Understanding thresholds and regime shifts is considered critical to
adaptability and transformations in transboundary basin management (Green
et al., 2013). In the case of upstream dependency, we would distinguish
between different system regimes depending on whether or not water scarcity
occurs and whether or not dependency occurs and its implication in the
prevention of scarcity. Dependency occurs in a region when there is a
transition between scarcity system regimes when considering cases where
water is or is not available from upstream. We therefore compare whether
scarcity occurs when water availability is calculated using solely local
runoff, natural discharge (sum of local runoff and upstream runoff), and
actual discharge (subtracting upstream water withdrawals from natural
discharge). System regimes categorised as “Scarcity” and “No scarcity” are
distinguished by a change in
Transitions in system regimes in terms of dependency can occur over time,
and regions can be classified according to their dependency category. Based
on the role of upstream inflows and withdrawals, a region might experience:
(i) no dependency if scarcity is not affected by upstream inflows,
(ii) “hidden” dependency if scarcity is altered by upstream inflows but not by
upstream water withdrawal, or (iii) “open” dependency if scarcity is altered after
accounting for upstream water withdrawals. If a system transitions into a
hidden dependency regime, the
Key terminology used in the analysis and their definitions. Note: definitions in terms of water availability volumes emerge from our analysis, as described in Sect. 2 and summarised visually in Fig. 4. Our analysis method did not consider the case where actual discharge may be greater than natural discharge.
A summary of the key terms used in the analysis is given in Table 1.
These definitions of upstream water dependency and dependency categories
form the basis of our quantitative analytical framework. The framework is
used to conduct a global analysis that quantitatively distinguishes
different scarcity and dependency regimes at a transboundary sub-basin
scale, i.e. parts of basins that belong to different countries. Figure 1
summarises the key ideas of this paper. Specifically, we aim to answer the
following research questions:
What is the current dependency category of each sub-basin? How do climate, upstream withdrawals, and local demand influence
the dependency category? What transitions to other dependency categories are
possible that should perhaps be considered in planning for the future? How do regime shifts involving hidden and open dependencies relate to
negotiations in transboundary basins?
Our analysis is based on modelled water availability and water use data
(Sect. 2.1). Our Methods section builds up our analytical framework, defining
sub-basins and calculating the different types of water availability (Sect. 2.2.1),
interpreting upstream dependency in terms of water scarcity (Sect. 2.2.2),
and unpacking determinants of dependency categories and transitions
between them (Sect. 2.2.3). Applying this method to global transboundary
basins, our results describe dependency categories in the year 2010 and how they
affect the problems faced by the sub-basins (Sect. 3). We then describe how
the transitions between scarcity and dependency system regimes affect
negotiation with upstream sub-basins to avoid the need to cope with scarcity
(Sect. 4.1). We conclude with a discussion of opportunities for further work
building on and improving this method and dependency typology (Sects. 4.2 and 4.3).
Datasets used in the study together with their source.
Key ideas of this study: our definition of dependency and themes addressed by our research questions.
To operationalise our definition of upstream water dependency, we used the global hydrological model PCRaster Global Water Balance (PCR-GLOBWB) to simulate water use and water availability at grid cell resolution (30 arcmin or roughly 50 km by 50 km at the equator). A basin–country mesh was used to subdivide the transboundary basins into sub-basin areas (SBAs). We then examine differences in the scarcity of available water of the different types in order to provide a first explanation of why dependency occurs. Below we present in more detail the data, methods, and analytical framework used for the assessment.
The data used for the study are summarised in Table 2. Runoff and water withdrawals (WWs) were calculated using the PCR-GLOBWB 30 arcmin model (Wada et al., 2011a, 2013; Wanders et al., 2018). PCR-GLOBWB is a conceptual, process-based water balance model. In brief, it simulates for each grid cell and for each time step (daily) the water balance in two vertically stacked soil layers and an underlying ground water layer, as well as the water exchange between the layers and between the top layer and the atmosphere (rainfall, evaporation, and snowmelt) (Wada et al., 2013). Discharge estimates from the model are extensively validated against observations from the Global Runoff Data Centre (GRDC) in existing publications by Wada et al. (2013, 2014). The return flows from industrial and domestic sectors have been taken into account in PCR-GLOBWB and the recycling ratios for industrial and domestic sectors have been estimated (roughly 40–80 %) at a country level and validated based on Wada et al. (2011a, 2014).
Total WW was calculated for each SBA as the sum of three water use sectors: irrigation, domestic, and industrial. The water use data for these sectors were obtained from the same model as the discharge simulations (Wada et al., 2011a, 2013; Wanders et al., 2018). Water use estimates have also been previously validated against reported country data, notably FAO AQUASTAT, by Wada et al. (2011a). In this analysis, water withdrawals refer to the total amount of water withdrawn, but not necessarily consumed, by each sector, much of which is returned to the water environment where it may be available to be withdrawn again. However, estimation of return flows is uncertain and they may not necessarily be available to downstream users, for example because of pollution, timing of the flows, or infiltration to groundwater (Wada et al., 2011a, b). Thus, the return flows were not subtracted from withdrawals in this analysis.
To provide an indication of need for water (rather than withdrawals), population density information was obtained from the HYDE 3.2 dataset for each year from 1981 to 2010 (Klein Goldewijk et al., 2010). The data were first aggregated from 5 to 30 arcmin resolution and then for each SBA for every year over the 30-year period.
The 30 arcmin raster dataset DDM30 (Döll, 2002) described drainage direction for both surface flow routing in PCR-GLOBWB and definition of upstream–downstream links.
Upstream–downstream relationship between sub-basin areas (SBAs) in the Oder basin and average simulated annual water availability for 1981–2010. Drainage network and sub-basin division are based on DDM30 (Döll, 2002) and country borders (Natural Earth, 2017) with additional manual assignment of border cells.
Country boundaries were first rasterised from Natural Earth admin 0 boundaries (Natural Earth, 2017). Border cells were then manually assigned to countries to provide meaningful hydrological relationships. In general, single cell SBAs were avoided. Cells where country borders follow a river were treated as separate “shared” zones. What we refer to as a “country” raster therefore includes both countries and shared zones.
To explain the methods and analytical framework used for the global assessment, we use the Oder – a river in central Europe – as an example case study (Fig. 2). The Oder is a transboundary river that rises in the Czech Republic and flows through western Poland, later forming the border between Poland and Germany. We chose the Oder river basin as an example case study because (i) it has non-trivial but sufficiently easy hydrological connections for illustrative purposes; (ii) it includes upstream, middle stream, and downstream SBAs; and (iii) the water stress levels and downstream dependencies illustrate well the use of our analytical framework.
SBAs were defined by breaking up the drainage
direction map where it flows across country (and shared zone) boundaries,
effectively yielding a mesh of river basin and country boundaries.
Upstream–downstream relationships between these SBAs were defined by the
flow direction dataset. The construction of the country raster (see Sect. 2.1)
ensured that the SBAs provide a meaningful representation of the
hydrological system. A country can have multiple SBAs in order to capture
different flow paths. In general, the drainage direction raster captures
major tributaries even if finer details are missing. In the case of the Oder
basin, Fig. 2 presents the four identified SBAs
(OdSBA
Three types of average annual water availability (for 1981–2010) were
calculated in each of these SBAs, corresponding to local water (local
runoff), total inflows including upstream areas (natural discharge), and
total inflows after upstream WWs (actual discharge) (see detailed
definitions in Table 1). We approximate discharge
as the sum of local runoff in local and upstream SBAs, such that there is an
arithmetic relationship between the two. This provides an easy-to-follow
abstraction of the problem that emphasises upstream–downstream relationships
while ignoring issues of land use change, timing of flows, and conveyance
losses. WW for each SBA was calculated separately (referred to as
Actual discharge (
Looking at the average availability of water (1981–2010) for the SBAs of the
Oder basin provides an illustration of the concept of upstream dependency
(Fig. 2). The headwater SBA (OdSBA
Dependency on upstream water can be assessed by comparing an SBA's scarcity category across the different water availability types (i.e. local runoff, natural discharge, actual discharge – see definitions in Table 1). We calculated scarcity using water stress and water shortage indices. Water stress refers to impacts from high use of water, while water shortage refers to impacts from insufficient water availability per person (Falkenmark et al., 2007; Kummu et al., 2016).
The stress indicator was calculated as
Annual stress and shortage were calculated using WWs and population for 2010
with (1) local runoff, (2) natural discharge, and (3) actual discharge.
Equations for water stress are
Scarcity and dependency category for the Oder sub-basin areas (SBAs)
under annual average conditions. The Falkenmark matrix
Definition of potential upstream water dependency categories. Dependency categories are obtained by summarising three letter codes representing the scarcity category using local runoff, natural discharge, and actual discharge respectively (see definitions in Table 1).
None of the SBAs have any shortage as the per capita water availability has
never dropped below 1000 m
In order to evaluate possible responses to dependency, we need to understand
what determines a dependency category and what can be done to achieve or to
avoid change. Annual water availability can be thought of as a constraint on
the environment in which a society operates. Society is able to influence
that constraint, for example by building reservoirs (Veldkamp et al., 2017) – captured
to some extent by the model. However, for a given hydro-climate
and state of development, it is useful to think of the current water
availability regime as an integral, defining characteristic of a system
regime. As population and WW increase in a region, the occurrence of
shortage, stress, and upstream dependency is determined by the volumes of the
three types of water availability. A region will face scarcity or dependency
as a result of
insufficient local runoff ( insufficient discharge, from local runoff and possible upstream inflows
( insufficient discharge after upstream WW (i.e. water withdrawals)
(
From a resilience perspective, these volumes of water can be thought of as
thresholds, where an SBA would be under the “No scarcity” category when its
average local runoff (
Typology of possible transitions in dependency category, as local water
demand or upstream water withdrawals (WW) increase or decrease
Dependency categories for each sub-basin area (SBA) for the year 2010
using
Figure 5 shows the ordering of possible thresholds
for an SBA based on water availability, and how the shortage and stress
categories vary as demand changes. To allow comparison, water availability,
population, and withdrawal are all expressed as percentages respectively of
Number of SBAs under different dependency categories in the year 2010.
So far, we have conceptualised change in dependency category in the context
of a fixed set of water availability thresholds, obtained directly from
estimated water availability volumes. The order of thresholds determines the
transition in dependency category as local demand increases or decreases. In
fact, even if upstream WW changes the values of the thresholds, their order
will remain the same. These scarcity thresholds are naturally ordered
because local water necessarily becomes insufficient before upstream water
availability types: local
Headwaters are the simplest case. Given they are the most upstream SBAs, they rely solely on local runoff, Increases in an SBA's demand cause a transition from “No scarcity” to the “Scarcity” category. Decrease in demand would have the opposite effect (Fig. 5).
In the case of middle stream and downstream SBAs, transition occurs between four scarcity categories, which are connected by a simple map of transitions: NNN-SNN-SNS-SSS. Transition in the scarcity category depends on both local demand and upstream WW. The experience of dependency in the Oder basin is therefore generally applicable to all middle and downstream SBAs. As the local demand increases, the SBA moves from NNN to SNN, exposing it to a “hidden dependency” as local runoff become insufficient, but the SBA still receives sufficient upstream inflows to meet the local demand. The next transition between SNN to SNS is dependent on both local demand and upstream WW until local demand increases to the level where all available water become insufficient – the SBA becomes SSS. The decrease in local demand and upstream WW will have the opposite effect.
Thus SBA crosses thresholds which not only change the scarcity category but also change the dependency category, considered in this study as transitions between different “system regimes”. Note that we focus on the effect of increasing or decreasing local demand and upstream WW, leaving changes in water availability to future work.
The analysis was applied to 246 international transboundary basins to understand the dependency category of these basins and possible future transitions, using WW and population data from 2010.
The 246 transboundary basins were divided into 886 SBAs based on country borders (as well as shared zones along those borders). As shown in Table 3, in the case of stress, most SBAs had no dependency in 2010 (93 %, 824 SBAs), while 52 SBAs have a hidden dependency – water available from upstream lifts the SBA from scarcity and upstream WWs do not change the scarcity category (though they may still intensify scarcity where it occurs, see the Discussion section). In total 10 (1 %) SBAs are identified where the dependency was open, meaning that upstream water withdrawals change the downstream stress category (Table 3). In the case of shortage, 35 SBAs were under hidden dependency and only 2 under open dependency. Upstream WWs thus only rarely play a role in causing low water availability per capita.
“No dependency” is observed in 93 % of cases for stress and 96 % of cases for shortage (Table 3). It is worth noting that scarcity can still be experienced without a dependency – it simply means that current upstream inflows (and WWs) do not influence whether scarcity occurs. For example, in the case of water stress, 41 % of the population living in SBAs under “No dependency” are under stressed conditions (Table 3). Further, even if an SBA in question is under no dependency category, upstream WW might still intensify the possible scarcity. In this category, there is not currently a problem with relationships with upstream SBAs, but to plan ahead, we need to understand how the situation could evolve, as is discussed in Sect. 4.1.
“Hidden dependency” is observed for both stress and shortage mostly in Africa, some parts of Southeast Asia, and Europe (Fig. 6a and b). Hidden dependency means that maintaining good relationships and assessing water use and potential changes with upstream basins are important to avoid scarcity. A number of SBAs in which currently no scarcity is observed (Fig. 6) are actually subject to upstream dependency. If inflows were to decrease sufficiently due to increased upstream WWs, scarcity could occur. In these SBAs, this has not yet happened, though upstream WWs may be influencing the intensity of scarcity and the level of development (population or use) at which thresholds occurs. Therefore, understanding of how the situation can evolve is needed to know how to manage the relationship with upstream water users.
“Open dependency” occurred notably in central Asia and some parts of North America for stress and for shortage, only in areas categorised as shared zones as part of the Jordan basin (Israel, Syria, and Lebanon) and the intermittent Wadi Al-Batin (forming the border between Kuwait and Iraq) (Fig. 6a and b). Open dependency indicates that scarcity occurs and could be attributed to upstream water use, such that there is a potential for tension with upstream water users over water allocation as things currently stand. But while there would be no scarcity if it were not for upstream WWs, reducing local water needs or WWs could also avoid shortage or stress. As a result, avoiding scarcity in these SBAs requires cooperation rather than uncoordinated competition between the upstream and the downstream regions. Such a situation is already evident in the case of central Asia (Dukhovny, 2014). However, understanding of the evolution of the situation may show that small decreases in local or upstream WWs may not be sufficient to avoid scarcity or dependency. It may be necessary to find a means to reduce needs or adapt to impacts from high water use.
In this analysis, transboundary water dependency was examined based on the concept that an SBA is dependent on upstream inflows if it requires those inflows to avoid water scarcity (e.g. stress, shortage as used here) and associated impacts. We proposed that regime shifts discussed in the resilience literature provide a useful way of thinking about this problem, and we provide a first exploration of how this concept can be analysed.
We aimed to address three research questions. Firstly, we identified the current dependency category of each SBA. Examining occurrence of scarcity with different types of water availability allows for the classification of ways in which upstream and downstream SBAs are dependent on each other (Sects. 2.2.2 and 3). To answer the second question, we further developed the analytical framework by explaining how climate, upstream withdrawals, and local demand influence the dependency categories (Sect. 2.2.3). This yields a sequence of transitions between system regimes that describe what future changes in scarcity and dependency are possible. This leads to our third research question: how does this relate to water management and negotiations in transboundary basins?
The literature on resilience and complex adaptive systems emphasises that it
is difficult to predict what will happen in the future, but we can identify what
are the transitions that
Understanding these transitions provides a basic level of guidance for a region. In a no dependency system regime (e.g. most SBAs analysed), efforts can be made to keep water demand at low enough levels to be self-sufficient. If water demand is expected to increase, monitoring is useful to avoid being surprised by the breaking of a hidden dependency. While our analysis shows relatively few open or hidden dependencies in 2010, population growth and associated water demand means that the need for water scarcity-related negotiation in transboundary basins could become a much greater issue in the future. It is specifically the emergence of dependencies that introduces the need for negotiation. Treaties have an indirect effect on physical upstream water dependency by limiting or coordinating development of water resources locally and upstream. Treaty design can be innovated to include functions that improve the stability of the dependency and hence prevent scarcity from occurring. If decision makers cannot avoid a transition to scarcity (i.e. an open dependency), perhaps due to factors outside their control, then coordination can at least facilitate adaptation to cope with physical water scarcity. There are regions where physical water scarcity is to some extent expected – development is limited by water availability, such that fully utilising other resources (e.g. land) requires more water than is available. In addition, it should be pointed out that negotiation for rights to upstream inflows is only one strategy among many to try to meet water demand. In such cases, treaties can focus on mitigating the severity of impacts of scarcity.
Downstream areas with increasing water demand should be mindful that, in a way, they are “choosing” to have to deal with dependencies and potential scarcity. If upstream withdrawals are stable, it can be argued that any conflict is effectively of their own making. Scarcity and dependency only emerge as problems when local demand crosses a threshold. This gives the impression that it is the local user that is responsible for the new problem, even though it may simply be that they are late to the game. On the other hand, if upstream withdrawals later increase, downstream regions might argue that they would not need to deal with scarcity, were it not for upstream actions. These interpretations of responsibility rely on the idea of precedence. The precedence paradigm is visible in prior appropriations regimes in the USA, while negotiated allocations are arguably implemented by water markets in Australia and elsewhere (Grafton et al., 2011). Even in a negotiated approach, however, existing water needs and WWs are often taken into account, including at an international level – hybrid approaches are common. The UN Watercourses Convention of 1997 also refers to the no harm principle (article 7), which works in tandem with consideration as to whether a given water use is reasonable and equitable (UN Watercourses Convention, 2018). These examples illustrate the close connection between water allocation and different views about responsibility for transitions.
Our work distinguishes between dependency and scarcity and recognises that dependency is primarily about potential for future scarcity, which transboundary cooperation aims to mitigate. To judge the importance of transboundary cooperation, it is more important to look at areas under no scarcity which are dependent on upstream inflows. The “open dependency” category (SNS) and SSS only include cases where institutional arrangements have failed to prevent scarcity from occurring. Our work, however, highlights that negotiation to avoid needing to cope with scarcity is only part of the issue. As demand increases, negotiation among riparian countries will eventually turn to discussion of intensity and frequency of scarcity, and the level of demand at which it occurs. Other existing work also distinguishes different types of rivers and basins to help understand why some riparian countries on international rivers have been able to successfully negotiate treaties and others have not – taking into account, for example, size of population, GDP, upstream–downstream relationship, and asymmetries in economic and political power among riparian states (Delbourg and Strobl, 2012; Song and Whittington, 2004; Wolf et al., 2003). Increasing water scarcity has been identified as a risk factor, but has not previously been systematically explored in terms of upstream dependency. Our dependency category typology complements this existing work, and relations to other typologies could be explored in the future.
One of the main advantages of our analytical framework, compared to existing knowledge, is that it highlights the possible “hidden” dependency of upstream water, which has not been assessed in these terms before. Previous studies on transboundary river basins identified clear evidence of the impacts of upstream water use to downstream water availability and water scarcity level (Al-Faraj and Scholz, 2015; Munia et al., 2016; Nepal et al., 2014; Veldkamp et al., 2017). It has already been found that about 0.95–1.44 billion transboundary people are under stress because of local water use, while upstream WWs increased the stress level by at least 1 percentage-point for 30–65 SBAs, affecting 0.29–1.13 billion people (Munia et al., 2016). Our analysis provides a different view of the issue by revealing that 386 million people (14 % of the total transboundary population) are dependent on upstream water to avoid possible stress because of their own water demand and 306 million people (11 % of the total transboundary population) are dependent on upstream water to avoid possible shortage (Table 3). Along with previous work, including a broader discussion of hydro-political dependency (Brochmann et al., 2012; Giordano and Wolf, 2003; Gleick, 2014; Jägerskog and Zeitoun, 2009; Mirumachi, 2013, 2015; Wolf, 1998, 1999, 2007), our analysis highlights the importance of local demand in causing scarcity and dependency. If local demand stays low enough and local water resources are sufficient to meet the demand, neither scarcity nor dependency occurs, and transboundary cooperation is not needed. This point has been made in existing literature (e.g. related to social construction of scarcity) but is not yet widely recognised.
In our analysis, we used WWs, which refer to the total amount of water withdrawn, but not necessarily consumed, by each sector; much of which is returned to the water environment where it may be available to be withdrawn again. The return flows from industrial and domestic sectors have been taken into account in PCR-GLOBWB and the recycling ratios for industrial and domestic sectors have been estimated and validated at a country level based on Wada et al. (2011a, 2014). However, in this paper, estimation of return flows is uncertain and they may not necessarily be available to downstream users, for example because of pollution, timing of the flows, or infiltration to groundwater (Wada et al., 2011a). We therefore did not include return flows when calculating water stress, but those could be taken into account in the future.
EFRs (i.e. environmental flow requirements) are important in transboundary water management. The stress indicator used in the analysis includes EFRs, assuming 30 % of the water is needed to satisfy the EFRs (Falkenmark et al., 2007). We do not account for EFR in a spatially disaggregated way as the analysis is conducted at the SBA scale, where spatially variable EFRs influence the dependency category, adding additional complexity to the transition map. EFRs are in any case a rather complex issue and not easy to quantify (Pastor et al., 2014). Global scale EFR methods could be criticised for not adequately capturing on-the-ground conditions – our treatment of environmental flows is fit for purpose given that our focus is on the resilience-based analytical framework.
Nuances of water availability were not taken into account in this analysis.
Industrial or domestic pollution may occur in upstream parts of a basin,
which might make water unusable for irrigation or domestic purposes (Thebo
et al., 2017). Availability of green water has not been considered either.
Green water increases the amount of locally available water by including
soil water in addition to runoff. This affects scarcity, as the need for
blue water should vary in response to changing green water availability,
e.g. when there is less green water available, more blue water is needed.
Decreases in availability of blue water (e.g. due to upstream withdrawals)
may also push a region to use more green water. While green water is an
important part of the local water availability, it does not affect inflows
from upstream, by definition. Water is called “green water” when
evapotranspiration occurs directly from rain or soil water, without runoff
occurring. There is no additional effect on
The main emphasis of the paper was the development of the analytical framework to understand the concept of upstream dependency from a resilience perspective. In this study, we provide the first attempt to link the dependency order to management strategies that could be taken to ease the possible scarcity situation. In future studies, in order to evaluate which transitions are actually plausible in the future, the analytical framework could also be applied to water availability and demand scenarios based on future climate change scenarios (representative concentration pathways, RCPs; Van Vuuren et al., 2011) as well as shared social pathway scenarios (SSP; O'Neill et al., 2014). In doing so, the scarcity criteria could also be revisited, given the simplicity of the indicators and thresholds used here, as acknowledged in Sect. 2.2.2. The analysis can be integrated with the concept of “adaptation tipping points (ATP)” to understand what strategies are needed (Kwadijk et al., 2010) to cope with the scarcity status. Additional insights may be gained using other thresholds and/or other water scarcity indicators, such as food self-sufficiency (Gerten et al., 2011; Kummu et al., 2014) or sustainability of water withdrawals (Wada and Bierkens, 2014). Future work could also quantify “distance” from a threshold, which would further address the distinction between how close these basins are to scarcity.
Our method was applied here at the basin scale, considering only international transboundary basins. It can, however, also be applied to understand the dependency at different scales to interpret, for example, more localised water dependencies, e.g. between states within countries (Garrick, 2015). Moreover, instead of using average water availability, analysis can be performed using water availability for each year to capture variability. Thus, the evolution of scarcity and dependency of an SBA for a given climate can be categorised into different transition pathways along which an SBA progresses as its water demand or water availability changes. An early attempt at this was made in the “discussion paper” version of this article (Munia et al., 2017). In connecting to management, the relevance of frequency of scarcity could be further examined in order to provide a more meaningful distinction between scarcity that occurs every year and scarcity that occurs in some year: at what frequency of scarcity do management options need to be implemented permanently rather than only adaptively e.g. trading of temporary vs. permanent water allocations (Bjornlund, 2003).
In this paper, we aimed to explore the relationships between SBAs (i.e. sub-basin areas) of global transboundary river basins, in terms of dependency of downstream on upstream inflows to meet water demand and avoid shortage and stress. Transboundary water dependency was examined through changes in scarcity category across different types of water availability (runoff, naturalised discharge, and actual discharge). We used the idea of regime shifts to illustrate the importance of dependency for basin management. The advantage of thinking in terms of thresholds is that we can reason about how scarcity and dependency might change in the future. In this paper, we focused on the effect of local demand and upstream water withdrawals, leaving possible changes in water availability, due to climate change for example, to future work. Understanding of the dependency category of an SBA has important policy implications regarding negotiation and redistribution of water among stakeholders, which may assist in improving water management in transboundary basins.
Results of the analysis and sub-basin areas are provided
in the Supplement. Input datasets are summarised in Table 2, and water availability and water use data
are available at
The supplement related to this article is available online at:
The authors declare that they have no conflict of interest.
The work was financially supported by the Academy of Finland funded project
WASCO (grant no. 305471), Emil Aaltonen Foundation funded project
“eat-less-water”,