Transboundary closed or endorheic river and lake systems are among the most vulnerable to changes in demand and supply, exemplified by the drastic reduction in surface area and volume of the Aral Sea, Lake Urmia and Lake Chad in the last decades [1
]. The closed basins of Central Asia are particularly vulnerable; climate change threatens water supply from glacier systems and increases evaporative losses, while demand is rising [2
]. Uncertain climate projections, human decision making and natural variability of hydrological systems complicate risk management [4
]. The endorheic transboundary Ili-Balkhash Basin (IBB) illustrates these challenges.
The Ili River supplies 70–80% of annual inflows to Lake Balkhash, currently the largest endorheic freshwater lake (average volume 106 billion cubic metres (BCM) in Central Asia since the desiccation of the Aral Sea [5
]. The Ili River is the longest river shared between China (Xinjiang Province) and South East Kazakhstan (see Figure 1
), taking water from the Tian Shan mountains in Xinjiang to the Kazakh steppe. In the dry continental Central Asian region, the Ili is an important source of water for the growing cities, irrigated agriculture, energy industries and the RAMSAR protected wetlands in the Ili Delta [8
]. The reliability of Ili River flows to downstream Kazakhstan and conservation of Lake Balkhash, are the focal points of Sino-Kazakh hydro politics; thus far, parties have not established a volumetric water allocation agreement [12
]. Recent political and climatic changes fuel concerns over the future of Lake Balkhash, as competition for water resources between countries and sectors appears to be increasing [6
At the crossroads between West China and Central Asia, the IBB has a long history of trade and (irrigated) agriculture [16
]. However, recently socio-economic development in the basin has accelerated, in turn increasing uncertainty about its future. The region is receiving extensive (foreign) investment for infrastructure, food production and hydropower development through the Silk Road Economic Belt (SREB), part of the Belt and Road Initiative (BRI) championed by China since 2013 and earlier through the western development policies [17
]. The $
1 trillion BRI, pitched as a ‘win-win’ programme, has become contentious in Central Asia. Whilst embraced by governments, public sentiment perceives agricultural investments as land grabs. Though research shows BRI investment does not affect food security in Kazakhstan [19
], widespread sinophobia turns communities against the initiative [20
]. Here agriculture in the arid north-west of China is undergoing rapid modernisation and organisational changes under the BRI agenda [18
]. Between 2000 and 2015, cropland under irrigation increased by 17% in the Chinese upstream section of the basin, accompanied by a marked increase in water consumption [7
]. Estimates suggest that agriculture consumes 90% of water in the basin, yet the estimates of the extent of agricultural land use in the Chinese Ili basin are limited and vary significantly due to access restrictions and data limitations [7
]. Therefore, discussions over planned (agricultural) development for the next decades remain speculative, impeding water management decision-making.
The IBB is also a climate-sensitive region. Although there are no studies on potential implications of global climate change for water management in the Ili basin, regional assessments offer some insight. Overall, climate projections from Global Circulation Models (GCMs) predict at least 1 ℃ of warming by 2060 relative to 1986–2005, particularly in winter [26
]. Warming is already affecting the basins hydrology, with glacial melt accelerating and shifts to earlier meltwater peaks [27
]. For precipitation, projections are less in agreement and GCM, IPCC regional assessments, and studies in adjacent basins suggest rainfall may decrease, remain stable or even slightly increase, depending on the GCM used [2
]. GCM performance across Central Asia is also debated, as the mountainous topography and lack of field measurement data complicate down-scaling [29
]. While changes in temperature and rainfall are likely to affect river flows, the diverging projections and methodological limitations introduce uncertainties on the magnitude of such changes, thus complicating adaptation strategies.
Although previous research provides insights into the potential threats to water security in the basin [6
], and given the pressing issues that the catchment and region face, no study has explored the combination of natural hydrological variability, climate change, and demand change. Given the wide range of uncertainties in understanding future climatic and demand pathways, we employ a scenario-neutral decision-scaling approach to quantify future vulnerability and reliability of the IBB [32
]. In contrast to top-down downscaling in vulnerability analysis, this methodology uses a bottom-up approach, which tests a wide range of potential futures to explore vulnerabilities of a system [33
]. Furthermore, this study is the first to evaluate vulnerabilities within an uncertainty approach in a river basin in Central Asia specifically and to explicitly integrate transboundary water risks in the BRI context. In doing so, this study offers insight into a wide range of potential stressors on the basin in the near future to inform water management decisions.
2. Study Area
The Ili-Balkhash basin has a total catchment area of 140,000 km2
. The Ili River is 1492 km long, and receives a combination of snow melt, glacial melt, and rainfall with peak flows during the growing season (June, July and August) [5
]. The downstream region is arid (average precipitation 120 mm), whereas the mountainous upper Ili is semi-arid with a strong precipitation and temperature gradient following topography (200 mm/year in the lower valley to 800 mm/year in the highest region) [37
]. As average precipitation in Xinjiang province is 165 mm/year, the Ili Valley is considered one of the most fertile areas of the arid north-west China [16
The Ili supplies water to competing sectors. The Kapchagay dam (364 MW; average length of reservoir 140 km, maximum capacity 28.1 BCM) provides energy to one-fifth of the Kazakh population [14
]. The Ili also supports the majority of irrigated agriculture in Kazakhstan and Xinjiang, although currently irrigated agriculture in the lower basin is small compared to the Chinese Ili Valley [16
]. The maximal potentially irrigated land in the Chinese Ili region is estimated at 12,000 km2
], yet there is disagreement on the current area under irrigation (7350 to 8085 km2
in 2014/2015) in the Ili Prefecture due to limited data availability and reporting [7
In an attempt to mitigate potential transboundary environmental impacts of domestic development, the local Ili government published an “Environmental Protection Plan” (EPP) in 2015 [43
]. The EPP states that by 2030 water consumption for direct production and living in the Chinese Ili basin should be limited to 7.122 BCM [43
]. The lower reaches of the Ili, from the Kapchagay reservoir to Lake Balkhash, form a fertile delta with RAMSAR protected status [8
Based on the modelling results under the historical flow regime, the basin is prone to droughts and low-flow conditions even under moderate water use scenarios. This is confirmed by the observed gradual degradation of Ili Delta vegetation in the last 20 years [23
]. Interestingly, the water level of Lake Balkhash has remained stable over the past decades [64
], except for a rapid drop of the lake’s water levels between 1970 and 1990 to the lowest recorded in 1987 as a result of reduced water availability during the filling of the Kapchagay reservoir [5
]. This suggests that except for a sudden reduction in flows, the ecosystem has the capacity to absorb natural high and low flow shocks. An explanation currently under investigation is the buffering capacity of the extensive river delta water surfaces and groundwater dynamics (8000 km2
); remote sensing studies indicate that the surface area of small ponds and lakes in the delta fluctuate according to Ili flow conditions [9
Looking ahead, changes in rainfall and temperature regimes in the basin as a result of global climate change may force a shift in the hydrology of the Ili. Results in this study indicate that between moderate decreases and increases (−11% to +11%) in precipitation may cause a particularly large difference in quantitative water security outcomes downstream. Marsuryama and Kezer [67
] and Propastin [15
] also concluded that the Ili River is predominantly sensitive to precipitation changes, based on historical data. However, there is disagreement on precipitation projections in the Ili-Balkhash basin. Projections from the assessed GCMs for RCP4.5 range between a −5 and +10% monthly precipitation change by the 2060s. The wide range of precipitation scenarios chosen in this study, based on the scenario-neutral methodology [32
], proved useful to explore these sensitivities. As the small rainfall differences may yield variable security outcomes, future studies could explore more precipitation scenarios in a narrower range and smaller steps.
On the other hand, the positive impact of increasing temperature upstream on runoff and water security downstream should be interpreted carefully. Temperature changes primarily affect glacial and snowmelt flows in the basin [27
], and the Ili depends on glacier- and snow-melt for 15% of its flows per year, and up to 25% of flows during the growing season [27
]. In the ABCD(E) model, the snow- and ice-melt parameter was assumed to remain stable in the future, although this may change under climatic shifts too. There was too little data to establish such future trends at this moment. Nonetheless, in agreement with our results, several authors predict higher meltwater flows for the next decades as a result of higher temperatures [28
]. However, the glacial melt component of river flow may disappear after the “peak meltwater date”, and there is ongoing debate about the duration of high meltwater yields and water supply after the peak [71
]. A global study estimates this peak date to lie between 2030 and 2050 in the IBB [71
]. Scenario analysis by [72
] indicated glaciers may completely disappear by the 2090s in the Tian Shan under future warming of +6 °C. Therefore, the timescale is important, and the study timeframe (2020–2060) may not capture the post-peak dynamics. The hydrological model (ABCDE) does not address temporal dynamics of glacial melt specifically [47
] and there is further scope to explore impacts on evaporative losses as well. This study therefore offers insights into the dynamics of this high meltwater yield period but does not predict nor address water availability for far-progressed glacial degradation.
Above all, the results underline the potential influence of changes in upstream water use on downstream water availability for different water users, intensifying existing trade-offs. However, it remains difficult to discuss the likelihood of different future development scenarios due to large gaps in data as a result of the political situation in Xinjiang, the rapid change under the BRI policy agenda and agricultural modernisation throughout North-West China. China’s hegemony, reinforced by the BRI, leads to rapid change in cultivation practices and water regimes. The limited information available indicates that development plans for the next decades designate the Chinese Ili Prefecture as key grain-production area, with less attention for rice [11
]. Perhaps this makes demand scenarios 2 and 4 (both 50% rice cropping) less probable and more moderately increasing demands (scenario AC3 with 15% rice cropping) more likely. Agricultural development remains a priority area in the current Five Year Plan of the Chinese government, and land use change studies indicate continued conversion of scrub and grassland into irrigated agricultural fields [23
While expansion of agriculture in the upper Ili is likely, Kazakh development plans also warrant further exploration. Results of this modelling study suggest that reduction of downstream water demands may alleviate potential environmental water stress, although this is highly dependent on both the extent of upstream water use and climate trajectories. Recently researchers have called for re-examination of the water footprint of agricultural activity in the south of the Kazakh Ili basin, where intensive irrigated agriculture takes water from the small mountain tributaries that feed the lower Ili and Kapchagay reservoir [31
]. Although these tributaries are thought to contribute only a minor component of flows [5
], there is scope for further inclusion of these activities in assessments. While this study uses the modelling tools to explore the current governance status-quo, the RiverWare platform can be used to further explore different operating and allocation policies in the basin, focusing more on the social component and downstream agency within the water security concept. In addition, while this study limited its scope to the Ili, future research should explore dynamics in the whole Balkhash basin to include Kazakh agricultural and industrial water use plans as well. However, such specific analyses and trans boundary joint decision-making would require hydrological, operational and governance data from all involved parties. This currently remains the major challenge in the Ili-Balkhash Basin.
Despite the inter-dependence between sectors upstream and downstream in the IBB through their shared waters, it is unlikely that the political landscape will change drastically in the near future. Combined with the deep uncertainty about climatic trends, this underpins the need for further use of decision-making under uncertainty (DMDU) tools. While the study serves as a first step towards assessment of system performance and robustness, there is scope for further work. There are other criteria for vulnerability that may provide valuable insights, such as resilience (adaptability, persistence, transformability), and other locally defined categories [60
]. Furthermore, this study focused on the CMIP5 GCMs, while Regional Climate Models (RCMs) or other models may enrich the analysis. Additionally, the results of this study may be refined by using more advanced thresholds for the evaluation metrics, as shortage and reliability in downstream areas: criteria for environmental flows, energy production and irrigation demands were based on limited local documentation. Nonetheless, the results offer insights for regional decision makers and researchers on what might be the consequences of changes in the IBB, opening up new avenues of analysis and planning.
Despite the uncertainties that complicate environmental assessments, investments and decisions are already urgently required, as demands for food, energy and water continue to grow and the impacts of global climate change start to manifest in the basin. Results demonstrate the sensitivity of the quantitative, reliability component of water security to demand and climatic stressors. To advance understanding of water security for Lake Balkhash and to mitigate growing pressures on the system, several knowledge gaps need to be addressed. Studies should particularly focus on water quality, groundwater dynamics and environmental requirements to maintain the delta—three important components contributing to water security that were not further explored in this study. The Ili model developed on the RiverWare platform allows integration of any new data and policies to explore impacts of management strategies, and is therefore a simple model that may potentially support transboundary discussions, researchers and local decision-makers [74
The main finding relevant for near-term water management decisions is that different water demands and precipitation scenarios give widely different water availability outcomes, with low robustness of the assessed scenarios under the GCM projections. This calls for robustness as a key objective of any new and existing projects in the basin, planning for both increases and decreases in precipitation and upstream water use. Furthermore, results demand reconsideration of priorities in the basin, as mounting pressures also cause deeper trade-offs between sectors. In the lower Ili, such rethinking could consider drought-planning in dam operation of the Kapchagay reservoir and consideration of the high evaporation from the reservoir surface. Nonetheless, the competition for water between sectors under the current governance and operation remains a “wicked problem” [14
], prevalent in many basins in Central Asia [3
]. This research demonstrated the benefit of the bottom-up approach combined with the RiverWare modelling platform under data constraints. Exploring water user tensions and potential synergies, while integrating social and climatology uncertainty may prove useful for the many other transboundary basins in Central Asia under (perceived) stress, for example, the Irtysh (shared between China and Kazakhstan) and rivers in the Aral Sea basin.
This study primarily examines what will happen if China closes the tap and global climate change progresses throughout the 21st century. The future of the IBB is uncertain, as water demands are likely to increase to provide food and power to the burgeoning populations in the region. This study underlines the impacts of upstream development and (mis)management of downstream demands on water security in the whole basin. Brown [75
] observes that we live in a time where common optimal objectives are hard to formulate, and the new objective is to find a range of politically feasible solutions. Moving away from sensitivity analysis, the next step is to explore the locally feasible options that consider the political landscape in the basin, which is changing rapidly under the BRI. The political tension between the potential gains to be made from further development in other sectors may obscure the agenda for environmental preservation, yet this study emphasises the potential consequences of inaction in this wicked problem. Above all, this study demonstrates the need for transformation of the transboundary governance, to allow for more hands on the tap and a rethinking of local governance in the Ili-Balkhash basin.