Transboundary Basins Research Articles

Flow regime changes in the Lancang River, revealed by integrated modeling with multiple Earth observation datasets

The flow regime change of rivers, especially transboundary rivers, affected by reservoir regulations is evident worldwide and has received much attention. Investigating dam-induced flow regime alterations is essential for understanding potential adverse downstream effects and facilitating dialogue around coordinated water use in transboundary basins, such as the Lancang River Basin (LRB). This study explored the value of combining several types of satellite Earth observation (EO) datasets that monitor different water balance components to constrain the parameter space of lumped conceptual hydrological models. Thus, we aimed to reconstruct the natural flow regimes upstream and downstream of the cascade reservoirs. Specifically, reservoir water storage changes were first estimated using satellite imagery and altimetry datasets. Then, storage changes were combined with hydrological model simulations of reservoir inflow to estimate the regulated flow regime downstream. Our results showed that integrated hydrological modeling combined with EO datasets exhibited better overall performance. Continuous warming and drying of the LRB resulted in a decrease in discharge of approximately 47 %. By comparing the simulated natural and regulated flow regimes, we revealed the pivotal role of the Xiaowan and Nuozhadu reservoirs in regulating natural flows. The wet season shortens (approximately 45 days), the flood peak flattens, and the low flow in the dry season has primarily increases. The two reservoirs attenuated 50 % of the flood peaks in the wet seasons and mitigated droughts by releasing up to 100 % of the natural flows in the dry seasons at the China–Laos border. Overall, these results enhance the understanding of upper reservoir operation, and the approaches can be applied to studies of dammed basins under climate change scenarios when knowledge of the upstream area is limited.

SPI-3 Analysis of Medjerda River Basin and Gamma Model Limits in Semi-Arid and Arid Contexts

The Standardized Precipitation Index SPI-3, associated with three months of rainfall accumulation, is a drought index for detecting immediate drought impacts. The two-parameter gamma distribution, recommended by the World Meteorological Organization as the underlying distribution for estimating SPI, has shown limits in semi-arid and arid conditions with respect to the normality test for the resulting SPI series. Our purpose was to evaluate its relevance for the Medjerda River Basin (Tunisia), a transboundary basin where the climate classes are temperate, dry, and hot summer, as well as arid hot desert and arid hot steppe. When analyzing the time series of 144 stations from 1950 to 2018, we found that the normality Shapiro–Wilk test was rejected in 17% of the cases, which agreed with the literature review results. The transition season (August, September, and October) had the highest rejection percentage. Three factors were identified to explain the deviation from normality. We first identified the rate of occurrence of completely dry (zero rain) three-month periods. The higher the rate of occurrence was, the higher that the probability was of its rejecting the normality test. High sample skewness was the second influencing factor. Finally, a series where the Grubbs’ test of identifying outliers was rejected was more likely to show the SPI-3 series deviating from normality.

Glacial lake outburst flood hazard under current and future conditions: worst-case scenarios in a transboundary Himalayan basin

Abstract. Glacial lake outburst floods (GLOFs) are a major concern throughout High Mountain Asia, where societal impacts can extend far downstream. This is particularly true for transboundary Himalayan basins, where risks are expected to further increase as new lakes develop. Given the need for anticipatory approaches to disaster risk reduction, this study aims to demonstrate how the threat from a future lake can be feasibly assessed alongside that of worst-case scenarios from current lakes, as well as how this information is relevant for disaster risk management. We have focused on two previously identified dangerous lakes (Galongco and Jialongco), comparing the timing and magnitude of simulated worst-case outburst events from these lakes both in the Tibetan town of Nyalam and downstream at the border with Nepal. In addition, a future scenario has been assessed, whereby an avalanche-triggered GLOF was simulated for a potential large new lake forming upstream of Nyalam. Results show that large (>20×106 m3) rock and/or ice avalanches could generate GLOF discharges at the border with Nepal that are more than 15 times larger than what has been observed previously or anticipated based on more gradual breach simulations. For all assessed lakes, warning times in Nyalam would be only 5–11 min and 30 min at the border. Recent remedial measures undertaken to lower the water level at Jialongco would have little influence on downstream impacts resulting from a very large-magnitude GLOF, particularly in Nyalam where there has been significant development of infrastructure directly within the high-intensity flood zone. Based on these findings, a comprehensive approach to disaster risk management is called for, combining early warning systems with effective land use zoning and programmes to build local response capacities. Such approaches would address the current drivers of GLOF risk in the basin while remaining robust in the face of worst-case, catastrophic outburst events that become more likely under a warming climate.

Hydropolitical System Archetypes: Feedback Structures, Physical Environments, Unintended Behaviors, and a Diagnostic Checklist

Hydropolitics is defined as the systematic study of conflict and cooperation in transboundary water basins, affecting around 40% of the world’s population. There has been great advancement in studies endeavoring to explore linkages between hydropolitical drivers and hydropolitical situations in transboundary basins. To add to this, we posit that hydropolitics would benefit from a system thinking approach that has remained less addressed in the literature. For this purpose, considering a transboundary basin as a system, this study is built on the main principle of system dynamics, which implies that a system’s structure determines its behavior. Incorporating system archetypes into hydropolitics can provide a framework for assessing hydropolitical behavior according to the potential structure of archetypes. In this paper, we discuss five hydropolitical system archetypes and their feedback loop structures, the required physical environments, and potential unintended behavior over time. Finally, an example of a diagnostic checklist is presented that will help riparian states recognize patterns of behavior they may face in the future. This paper lays the groundwork for gaining insight into using system archetypes in projecting plausible hydropolitical behaviors and understanding past behaviors in transboundary basins.

Detecting Connectivity and Spread Pathways of Land Use/Cover Change in a Transboundary Basin Based on the Circuit Theory

Understanding the spatial spread pathways and connectivity of Land Use/Cover (LULC) change within basins is critical to natural resources management. However, existing studies approach LULC change as distinct patches but ignore the connectivity between them. It is crucial to investigate approaches that can detect the spread pathways of LULC change to aid natural resource management and decision-making. This study aims to evaluate the utility of the Circuit Theory to detect the spread and connectivity of LULC change within the Okavango basin. Patches of LULC change sites that were derived from change detection of LULC based on the Deep Neural Network (DNN) for the period between 2004 and 2020 were used. The changed sites were categorized based on the nature of the change of the classes, namely Category A (natural classes to artificial classes), Category B (artificial classes to natural classes), and Category C (natural classes to natural classes). In order to generate the resistance layer; an ensemble of machine learning algorithms was first calibrated with social-ecological drivers of LULC change and centroids of LULC change patches to determine the susceptibility of the landscape to LULC change. An inverse function was then applied to the susceptibility layer to derive the resistance layer. In order to analyze the connectivity and potential spread pathways of LULC change, the Circuit Theory (CT) model was built for each LULC change category. The CT model was calibrated using the resistance layer and patches of LULC change in Circuitscape 4.0. The corridor validation index was used to evaluate the performance of CT modeling. The use of the CT model calibrated with a resistance layer (derived from susceptibility modeling) successfully established the spread pathways and connectivity of LULC change for all the categories (validation index > 0.60). Novel maps of LULC change spread pathways in the Okavango basin were generated. The spread pathways were found to be concentrated in the northwestern, central, and southern parts of the basin for Category A transitions. As for category B transitions, the spread pathways were mainly concentrated in the northeastern and southern parts of the basin and along the major rivers. While for Category C transitions were found to be spreading from the central towards the southern parts, mainly in areas associated with semi-arid climatic conditions. A total of 186 pinch points (Category A: 57, Category B: 71, Category C: 58) were detected. The pinch points can guide targeted management LULC change through the setting up of conservation areas, forest restoration projects, drought monitoring, and invasive species control programs. This study provides a new decision-making method for targeted LULC change management in transboundary basins. The findings of this study provide insights into underlying processes driving the spread of LULC change and enhanced indicators for the evaluation of LULC spread in complex environments. Such information is crucial to inform land use planning, monitoring, and sustainable natural resource management, particularly water resources.

Effects of upstream activities of Tigris-Euphrates River Basin on water and soil resources of Shatt al-Arab Border River

The Tigris-Euphrates River Basin (TERB) is one of the key transboundary basins among the developing countries in the Middle East which has been significantly damaged by mismanagement, exploitation for energy production and unsustainable water use. This study aimed to evaluate the water and soil resources in the lower parts of this basin. More specifically, how the area of the Shatt al-Arab River (SAR) formed at the confluence of the Tigris and Euphrates rivers is affected in terms of quality by upstream activities. Four mathematical models of hydrodynamics, advection-dispersion in the river, and convection-dispersion in soil were used in conjunction with assessment of soil salinization by irrigation water. The soil salinization based on direct saltwater infiltration from riverbanks and soil salinization by irrigation with river water were predicted after simulating the intrusion of saline seawater by considering the tidal conditions of the SAR. The results showed that by applying six optimistic and probable scenarios of freshwater inflows for the future, changes in the water and soil quality in downstream riparian countries (Iran and Iraq) reflect this basin's developments and water allocation upstream. Regarding the possible scenario of maximum inflow reduction in the future, the findings of this study can be used to create a comprehensive view of the current condition and development challenges. This emphasizes the need for participatory crisis mitigation strategies between the upstream and downstream countries.

A review of hydro-hegemony and transboundary water governance

Abstract This review paper is an attempt to analyze the existing literature on hydro-hegemony (HH) theory, which has emerged to explain transboundary water interactions. The literature highlights that the conventional water interaction literature inadequately deals with three important factors: (i) asymmetric power relations, (ii) varying intensities of conflict, and (iii) the importance of the geographical location of riparian states. Since its emergence, it has evolved both in theory development and in application to transboundary basins. Although an attempt has been made earlier for reviewing, organizing and evaluating the overall literature on HH, the review itself is somehow silent on the hegemonic approaches to assess its contribution to the transboundary water governance literature and to identify the existing and future research gaps. This paper, however, not just addresses these omissions to (i) review the scholarly literature on HH; (ii) explore the challenges associated with power, cooperation, and conflict; and (iii) identify and explore potential trends in HH theory, but it also gives special attention to the hegemonic approaches within states’ boundaries and the ingredients to enrich the theory and research agenda of HH.

Quantifying the influences of climate change and human activities on the grassland in the Southwest Transboundary Basin, China.

The Southwest Transboundary Basin (STB), which contains a part of the Tibetan Plateau and Southwest China, covers a large area of grassland that has been experiencing significant climate change (Cc) and human activities (Ha). However, variabilities of the grasslands and respective contributions of the drivers have not been fully understood. In this study, we quantitatively investigated the influences of Cc and Ha on the grasslands from 1982 to 2015 across the STB, using residual analysis, trend analysis, and partial correlation analysis. Particularly, vapor pressure deficit (VPD), which is increasingly paid attention to in current studies, was included in our analysis as a critical driver of alpine grasslands. Additionally, a new method, pure climate-induced grassland pixel, which combined the coefficient of variation, was proposed to significantly improve the pixel purity with higher coefficient correlation and lower error and bias. Results show that changes in the climate play an important role in the grassland coverage of STB during 1982-1999 and 2000-2015, while Ha only had a relatively weak negative impact on grassland during 2000-2015, mainly in the Lancang River Basin. Specifically, the grasslands showed an increasing trend in 1982-1999, dominated by climate change with a contribution rate of 80.87%. Temperature had the greatest contribution, followed by VPD and precipitation in this period. On the contrary, the grasslands showed a decreasing trend in 2000-2015, dominated by both Cc and Ha with the contributions of 53.16% and 46.84%, respectively. The findings of this study provide a valuable reference for future ecological restoration in other similar alpine regions.

Where and When Does Streamflow Regulation Significantly Affect Climate Change Outcomes in the Columbia River Basin?

AbstractThe Columbia River basin is a large transboundary basin located in the Pacific Northwest. The basin spans seven US states and one Canadian province, encompassing a diverse range of hydroclimates. Strong seasonality and complex topography are projected to give rise to spatially heterogeneous climate effects on unregulated streamflow. The basin's water resources are economically critical, and regulation across the domain is extensive. Many sensitivity studies have investigated climate impacts on the basin's naturalized hydrology; however, few have considered the large role of regulation. This study investigates where and when regulation affects projected changes in streamflow by comparing climate outcomes across 80‐member ensembles of unregulated and regulated streamflow projections at 75 sites across the basin. Unregulated streamflow projections are taken from an existing data set of climate projections derived from Coupled Model Intercomparison Project version 5 Global Climate Models. Regulated streamflow projections were modeled by the US Army Corps of Engineers and the US Bureau of Reclamation by using these unregulated flows as input to hydro‐regulation models that simulate operations based on current and historical water demands. Regulation dampens shifts in winter and summer streamflow volumes. Regulation generally attenuates changes in cool‐season high flow extremes but amplifies shifts in warm‐season and annual high flow extremes at historically snow‐dominant headwater reservoirs. Regulation reduces dry‐season low flow changes in headwater tributaries where regulation is large but elsewhere has little effect on changes in low flows. Results highlight the importance of accounting for water management in climate sensitivity analysis particularly in snow‐dominant basins.

Identification and Diagnosis of Transboundary River Basin Water Management in China and Neighboring Countries

Numerous studies have demonstrated that a complex distribution of water resources, regional development, and management mechanisms create significant management challenges for transboundary river basins. We utilized diagnostic thinking to examine the water management issues of the 14 main transboundary watersheds in three regions (Northeast, Northwest, and Southwest) of China. Our four diagnosis points were water quantity, water quality, ecological stability and human health, and cooperation among watershed stakeholders. We found that the watersheds faced varying water management issues. The Indus and Ganges basins have the worst problems, whereas the Tarim basin’s ecological environment is the most vulnerable and the Ob basin is the fittest. Therefore, depending on each basin’s results, we provide practical water management ideas for each. Furthermore, we summarized and classified the geographical settings of each basin and determined the water management issues in each major region in China. Our results provide direction for both new research on and cooperation with transboundary basin water management.

Sediment quality in the Polish part of the trans-boundary Vistula Lagoon: implications for deposition management

The Vistula Lagoon is located in Europe and is the second largest lagoon in the Baltic Sea, after Curonian Lagoon. It is a transboundary water basin shared by Poland and Russia. The entire Polish part is a NATURA 2000 area. The whole lagoon area requires economic rehabilitation comprising integrated management involving ecological, social and economic interactions and couplings. Currently most of the actions and investments are devoted to development of local tourism and stimulation of local economy by construction of new marinas and small harbors. In Polish part this is enhanced by the Vistula Spit cross-cut construction. Such activities result in a need for expansion of navigational channels leading to their dredging and necessity of safe management of the dredged deposit. Investigations of sediment quality thus became indispensable. To assess its quality, sediment samples were collected in the Polish and Russian part of the Vistula Lagoon to evaluate and compare soil strength parameters and the concentrations of harmful substances in both parts. Due to the current political situation and interruption of scientific contacts between the Russian and Polish researchers only the results obtained for the Polish part are reported herein. The analysis revealed that the studied sediments are generally very weak in terms of strength parameters but safe as regards the presence of dangerous substances according to EU regulations. This allows for deposition in the form of artificial islands that will ultimately fulfill important ecosystem services and provide long term solution for the excess sediment management.

Potential distribution prediction of Deyeuxia angustifolia in the Tumen River Basin and analysis of major impact factors

Deyeuxia angustifolia acts as an indicator of the changes in wetland ecosystems and plays an important ecological role in their functions. Previous studies have shown that the Tumen River Basin is of wide global interest as a transboundary basin area with abundant wetland ecological resources. Despite the implementation of wetland conservation measures in recent years, the distribution area of D. angustifolia in this basin has been reduced due to climate change and anthropogenic activities. Therefore, we used MaxEnt and geographic information system to model a suitable habitat for this species, simulated changes in the habitat, and applied Jackknife to assess the influencing environmental variables. The Jackknife tests showed that slope orientation, solar radiation in September, and total nitrogen were the dominant environmental factors affecting the potential distribution of D. angustifolia. Compared to the current distribution, the total area of land highly and moderately suitable for this species will decrease in the 2050’s and 2070’s, respectively, under two representative concentration paths (RCPs), shifting the centroid of its suitable area and direction of wetland degradation to the northeast. Our study of the projected potential distribution of D. angustifolia in the basin under future climate change could provide important information for its conservation, management, sustainable use, and early warning to prevent its extinction.

Data sharing in transboundary water management

Half the world's population resides within 310 transboundary lake and river basins shared among 151 riparian nations. Approximately 60% of these basins lack cooperative frameworks to share water. The complexities of sharing water necessitate identifying approaches for managing transboundary international freshwater resources. While much has been written about the histories, theory, and mechanisms of transboundary water management, conflict, and cooperation among riparian nations, we draw attention to scholarship written about what we believe is the central tool for cooperation: data and data sharing. The 1997 United Nations' Convention on the Law of the Non-Navigational Uses of International Watercourses (UN Watercourse Convention) recognizes sharing water resources data is vital to river basin cooperation. Data sharing builds trust between riparian states, aids in mitigating conflict, and improves environmental, economic, and social outcomes. Despite calls to increase data sharing in transboundary basins to support cooperative management, few papers review the role of data sharing in transboundary water management, including how often and what types of water resources data and information are shared. We synthesize the role of data in conflict and collaboration from peer-reviewed papers on transboundary water management from the year the UN Watercourse Convention went into force, 2014 to May 2022. We outline what scholars argue are the types of water-related data to be shared, the frequency of data sharing, and the mechanisms for sharing data for facilitating cooperation in transboundary waters.

Changes in the Stability Landscape of a River Basin by Anthropogenic Droughts

As water resources enter the era of the Anthropocene, the process of anthropogenic droughts arises as the interplay between climate cycles and human-centered water management in rivers. In their natural conditions, rivers exhibit a natural hydrologic variability, wet and dry cycles, that are a vital property for promoting ecological resilience. Human activities alter the temporal variability of streamflow, a resilience property of river systems. We argue that anthropogenic droughts in river basins can lead to changes in the resilience properties of the system depicted in stability landscapes. This study aims to analyze anthropogenic droughts and the changes provoked to the stability landscapes of the streamflow system of a river basin. We use 110 years of regulated and naturalized streamflow data to analyze the hydrologic variability (wet periods and droughts) of a river system. First, we determined the streamflow drought index (SDI), and the results were assessed using probability distribution functions to construct stability landscapes and explore the resilience properties of the system. The transboundary basin of the Rio Grande/Rio Bravo (RGB) is used as a case study. Our main findings include evidence of resilience erosion and alterations to the properties of the stability landscape by the human-induced megadrought in the RGB, which resulted from extensive anthropogenic alteration and fragmentation of the river system. The novelty of this research is to provide a baseline and move forward into quantifying ecological resilience attributes of river basins in water resources planning and management.

A comprehensive geospatial database of nearly 100 000 reservoirs in China

Abstract. With rapid population growth and socioeconomic development over the last century, a great number of dams/reservoirs have been constructed globally to meet various needs. China has strong economical and societal demands for constructing dams and reservoirs. The official statistics reported more than 98 000 dams/reservoirs in China, including nearly 40 % of the world's largest dams. Despite the availability of several global-scale dam/reservoir databases (e.g., the Global Reservoir and Dam database (GRanD), the GlObal geOreferenced Database of Dams (GOODD), and the Georeferenced global Dams And Reservoirs (GeoDAR)), these databases have insufficient coverage of the reservoirs in China, especially for small or newly constructed ones. The lack of reservoir information impedes the estimation of water budgets and the evaluation of dam impacts on hydrologic and nutrient fluxes for China and its downstream countries. Therefore, we presented the China Reservoir Dataset (CRD), which contains 97 435 reservoir polygons and fundamental attribute information (e.g., name and storage capacity) based on existing dam/reservoir products, national basic geographic datasets, multi-source open map data, and multi-level governmental yearbooks and databases. The reservoirs compiled in the CRD have a total maximum water inundation area of 50 085.21 km2 and a total storage capacity of about 979.62 km3 (924.96–1060.59 km3). The quantity of reservoirs decreases from the southeast to the northwest, and the density hotspots mainly occur in hilly regions and large plains, with the Yangtze River basin dominating in reservoir count, area, and storage capacity. We found that these spatial accumulations of reservoirs are closely related to China's socioeconomic development and the implementation of major policies. Finally, we presented the comparison of the CRD with GOODD, GeoDAR, and GRanD databases. The CRD has significantly increased the reservoir count, area, and storage capacity in China, especially for reservoirs smaller than 1 km2. The CRD database provides more comprehensive reservoir spatial and attribute information and is expected to benefit water resources managements and the understanding of ecological and environmental impacts of dams across China and its affected transboundary basins. The CRD database is publicly available at https://doi.org/10.5281/zenodo.6984619 (Song et al., 2022).

Identifying Thresholds, Regime Shifts, and Early Warning Signals Using Long-Term Streamflow Data in the Transboundary Rio Grande–Rio Bravo Basin

As the centerpiece of ecosystems and human societies, river basins are complex social–ecological systems (SESs) that depend on the natural flow regime and the hydrologic variability to adapt to changes and absorb disturbances. Anthropogenic and climate change disturbances destabilize river systems. Therefore, a resilience question arises: What is the carrying capacity of a river basin, i.e., how much disturbance can a river basin take until the system undergoes a regime shift? To answer this question, this study aims to identify regime shifts, thresholds, and the carrying capacity of the transboundary Rio Grande–Rio Bravo (RGB) basin using 110 years of monthly streamflow data. To address this research question, first, gauged (regulated) and naturalized streamflow data is collected; if naturalized flows are not available, they are calculated through streamflow naturalization. Second, streamflow standardization is estimated using the streamflow drought index. Third, a regime shift assessment is performed using Fisher Index, and fourth, the nonparametric Mann-Kendall test is used to assess the Sustainable Regime Hypothesis which evaluates regime shifts and alternative regimes. Results demonstrate that resilience thresholds are surpassed, and regime shifts, including early warning signals, occurred in multiple locations of a transboundary basin. The present study highlights the importance of assessing the carrying capacity of a river basin; hence, evaluating regime transitions, including identifying early warning signals and thresholds, is critical in managing for sustainability and ecological resilience of SESs. Looking ahead, the integration of ecological resilience theory into water management has the potential to recognize the sustainable carrying capacity of river basins at the local, regional, and international scale.

Seeing beyond negotiations: the impacts of the Belt and Road on Sino-Kazakh transboundary water management

ABSTRACT China’s Belt and Road Initiative (BRI) and infrastructural development has led to growing concerns regarding the future of Central Asia’s water resources. However, few attempts have been made to assess the impacts this will have on specific transboundary basins within the region. This article explores how the context of the BRI transcends its physical impacts within the Ili and Irtysh basins, creating a sanctioned discourse that forecloses the possibility of ‘successful’ negotiations at an official level. As such, pathways to transboundary water management that exist beyond the negotiations are shown to have greater plausibility and potential effectiveness.

Using the WEI+ index to evaluate water scarcity at highly regulated river basins with conjunctive uses of surface and groundwater resources.

This paper discusses the role and limitations of using WEI+ as a water resource management tool for highly regulated river basins, with a conjunctive use of surface and groundwater resources. By considering flow regulation by reservoirs and aquifer systems, seasonality of water availability and demand, returns from water uses and environmental flow requirements, WEI+ constitutes an improvement to existing quantitative water scarcity indexes. However, the computation of WEI+ in complex river basins systems requires detailed data on water availability and water allocation to various uses, which are hard to obtain from monitoring records. The paper describes how the combined use of hydrological and water allocation models can help to overcome data gaps in water accounting and contribute to an improved analysis of water scarcity in heterogeneous and intricate river basins. It also examines the information provided by WEI+ and by other widely used water scarcity indexes, such as the Water Stress Index and the Criticality Ratio, as well as discusses the ability of WEI+ to measure the performance of hydraulic systems, usually evaluated by parameters such as reliability, vulnerability, and resilience. The Tagus River transboundary basin was selected as case study due to massive flow regulation by multi-purpose reservoirs and significant seasonality of water availability and demand. Results show the benefits of using WEI+ to define levels of water scarcity, over other indexes. Within the Tagus River systems, high values of WEI+ are reached during the summer months in regions with intensive agriculture, denoting severe water stress conditions in most sub-basins. The analysis also reveals the strong dependence of Portugal, the downstream country, on flows from Spain, the upstream country.

Identifying Major Hydrologic Change Drivers in a Highly Managed Transboundary Endorheic Basin: Integrating Hydro‐Ecological Models and Time Series Data Mining Techniques

AbstractThe fragile balance of endorheic lakes in highly managed semiarid basins with transboundary water issues has been altered by the intertwined effects of global warming and long‐term water mismanagement to support agricultural and industrial demand. The alarming rate of global endorheic lakes' depletion in recent decades necessitates formulating mitigation strategies for ecosystem restoration. However, detecting and quantifying the relative contribution of causal factors (climate variability and anthropogenic stressors) is challenging. This study developed a diagnostic multivariate framework to identify major hydrologic drivers of lake depletion in a highly managed endorheic basin with a complex water distribution system. The framework integrates the Soil and Water Assessment Tool (SWAT) simulations with time series decomposition and clustering methods to identify the major drivers of change. This diagnostic framework was applied to the Salton Sea Transboundary Basin (SSTB), the host of the world's most impaired inland lake. The results showed signs of depletion across the SSTB since late 1998 with no significant changes in climate conditions. The time series data mining of the SSTB water balance components indicated that decreases in lake tributary inflows (−16.4 Mm3 yr−2) in response to decline in Colorado River inflows, associated with state water transfer agreements, are causing the Salton Sea to shrink, not changes in the irrigation operation as commonly believed. The developed multivariate detection and attribution framework is useful for identifying major drivers of change in coupled natural human systems.

A framework for drought adaption under deep uncertainties: Application of Portfolio theory (Markowitz 2.0)

Hydrological uncertainty, climate change, and water infrastructure development upstream transboundary basins may affect the safe access to water resources downstream, making socioeconomic and biophysical subsystems vulnerable. Therefore, it is vital to apply decision-making approaches to reduce vulnerability, especially in arid and semi-arid basins. This study evaluated an adaptation framework to reduce vulnerability through optimal water allocation in drought-prone areas. This framework was implemented in an area dependent on upstream transboundary water (Helmand River Basin). An integrated system dynamics model was developed using socioeconomic and biophysical factors identified by the Füssel Vulnerability Framework. The climatic variables of the basin were simulated and predicted by the output of AOGCM models. The trend of upstream annual precipitation and temperature changes during the 2021–2050 period based on the RCP4.5 emission scenario was −2% and +1.9 C compared to those in the historical period, respectively. The results indicated the drought intensification due to a 13% decrease in future runoff (2050) compared to the base period, leading to a reduction in value-added agriculture (8%) and the population (31%). Therefore, the latest version of portfolio optimization called Markowitz 2.0 was used. In order to decide on potential long-term growth versus short-term loss, an efficient frontier was formed between the expected return and the conditional value at risk (CVaR) based on the Markowitz 2.0 model. According to the model results, the development of the industrial sector as an approach with moderate (reasonable) risk could increase financial return by 43% and allocation to the environmental sector by 2.3 times. Finally, prioritizing the environmental sector was a high-risk approach with high returns that increased efficiency by 45%. The results showed that the proposed framework could help decision-makers, based on their risk-taking level, activate and develop decisions on water resource allocation and water-dependent productive sectors on the basis of efficient frontiers.