Altered Hydrologic Regime Research Articles

Multi-Objective Ecological Long-Term Operation of Cascade Reservoirs Considering Hydrological Regime Alteration

Multi-Objective Ecological Long-Term Operation of Cascade Reservoirs Considering Hydrological Regime Alteration

Evaluating the hydrological regime alteration under extreme climate scenarios in Southeast China

Study regionThe Shanmei Reservoir Watershed (SRW), Southeast China. Study focusThis study investigated the climate and hydrological regimes alterations in a subtropical coastal watershed (SRW) during the 21st century in extreme scenarios. The extreme scenarios, i.e., warm-wet and cold-dry climates, were constructed using 18 global climate models (GCMs) from CMIP6 under shared socioeconomic pathways (SSP1–2.6, SSP2–4.5, SSP3–7.0 and SSP5–8.5). The Soil and Water Assessment Tool (SWAT) model and Indicators of Hydrologic Alteration (IHA) were applied to quantify the impacts of climate change on the eco-hydrological regimes during the projected period (2041–2100) compared to the base period (1980–2014). New hydrological insights for the regionThe results show that the average temperature rises by 0.6–3.8 ℃, and the average annual precipitation changes by −21.4 % - 32.4 % by the end of the 21st century under extreme scenarios. Contrasting hydrological regimes are expected in the SRW under extreme scenarios. Under the extreme warm-wet scenarios, the monthly runoff is lower during spring and higher during summer, the minimum flows are significantly higher, and the maximum and minimum flows occurs earlier. Water resource utilization and ecosystem health are expected to improve. However, the opposite holds true in the cold-dry scenarios. The hydrologic regime alteration under future extreme climate scenarios can guide local water planning and ecological restoration strategies.

Physically based vs. data-driven models for streamflow and reservoir volume prediction at a data-scarce semi-arid basin

Physically based or data-driven models can be used for understanding basinwide hydrological processes and creating predictions for future conditions. Physically based models use physical laws and principles to represent hydrological processes. In contrast, data-driven models focus on input–output relationships. Although both approaches have found applications in hydrology, studies that compare these approaches are still limited for data-scarce, semi-arid basins with altered hydrological regimes. This study aims to compare the performances of a physically based model (Soil and Water Assessment Tool (SWAT)) and a data-driven model (Nonlinear AutoRegressive eXogenous model (NARX)) for reservoir volume and streamflow prediction in a data-scarce semi-arid region. The study was conducted in the Tersakan Basin, a semi-arid agricultural basin in Türkiye, where the basin hydrology was significantly altered due to reservoirs (Ladik and Yedikir Reservoir) constructed for irrigation purposes. The models were calibrated and validated for streamflow and reservoir volumes. The results show that (1) NARX performed better in the prediction of water volumes of Ladik and Yedikir Reservoirs and streamflow at the basin outlet than SWAT (2). The SWAT and NARX models both provided the best performance when predicting water volumes at the Ladik reservoir. Both models provided the second best performance during the prediction of water volumes at the Yedikir reservoir. The model performances were the lowest for prediction of streamflow at the basin outlet (3). Comparison of physically based and data-driven models is challenging due to their different characteristics and input data requirements. In this study, the data-driven model provided higher performance than the physically based model. However, input data used for establishing the physically based model had several uncertainties, which may be responsible for the lower performance. Data-driven models can provide alternatives to physically-based models under data-scarce conditions.

Evaluation of instream ecological flows based on hydrological alteration in the Upper Huai River, China

Abstract Natural flow regime (instream ecological flow) is a vital element of ecological hydrology, serving a crucial role in the fundamental functions of river ecosystems. Intense human activities, especially reservoir operation, have unavoidably altered the flow regime of the Upper Huai River, leading to further impacts on river ecosystems. It is essential to quantify hydrological alterations in flow regimes and their associated impacts on river ecosystems for effective river water management. Ecological flow indicators, namely ecological deficit and surplus, were analyzed to assess instream ecological flow. The overall degree of alteration (Do) and the Dundee Hydrological Regime Alteration Method (DHRAM) were utilized to evaluate the degree of hydrological alteration. Additionally, the Shannon Index (SI) was employed to estimate the impact of hydrological alterations on ecological diversity in this study. The results reveal that the streamflow series underwent mutation in 1987, leading to a decrease in ecological surplus and an increase in ecological deficit. The overall alteration degree is 32%, with a DHRAM level of 3, signifying low hydrological alteration and moderate ecological risk in the region. Furthermore, the biodiversity of the river has markedly declined due to human activities following the alteration.

Evaluation of hydrological regime alteration and ecological flow processes in the changing environment of the Jialing River, China

Abstract Ecological flow is a key element in maintaining the biodiversity of a basin's aquatic ecosystem. This study quantifies the degree of hydrological regime alteration in the Jialing River and the contributions of various driving factors using the indicators of hydrologic alteration and range of variability approach (IHA-RVA), the river impact method (RI), and the elasticity coefficient method based on long-term hydro-meteorological data. Cross-wavelet analysis is used to reveal the periodicity and coherence of runoff and driving factors. Additionally, the improved Q90 method presents a more effective annual ecological flow process. The results show that the overall hydrological regime in the Jialing River has undergone a moderate change, with RVA and RI values of 45.02% and 0.66. Human activities contribute 54.68% to the changes in streamflow. Streamflow has an extremely significant correlation with precipitation and aridity index (Φ). Approximately 85% of the wavelet cone of influence (COI) area, tested at a 95% confidence level, falls within the region. The study also found that the ecological flow obtained through the improved Q90 method is more conducive to the healthy development of the river ecosystem in the Jialing River. These findings can provide some assistance for aquatic ecosystem restoration in the Jialing River.

A novel Joint Probability Density Difference Approach for assessing the alteration of hydrologic regime

AbstractThe construction and operation of upstream reservoirs have significantly altered downstream hydrologic regime. Appropriate and quantifiable assessment method for the alteration of hydrologic regime is considerably vital and emergent for ecological protection and restoration. The Range of Variability Approach (RVA) and modified RVA methods have been widely used in practice to assess the hydrological alteration. However, these methods have failed to concurrently describe the distribution of indicator and morphological features in detail, which might inevitably lead to the misjudgment of alteration. This paper proposes a Joint Probability Density Difference Approach (JPDDA) method to address the major drawbacks of these previous methods with the introduction of Gaussian Kernel Density Estimation (KDE) and copula function. The annual average flow is selected as the reference variable to construct a proper joint probability density function between itself and other hydrological alteration indicators. The JPDDA method could describe the marginal distribution in detail through Gaussian KDE and also link the morphological features with copula function. Along with pervious methods, the hydrological alterations at Yichang hydrological station, Yangtze River are estimated based on the measured flow from 1949 to 2022. It is shown that the hydrologic regime has suffered from a moderate or even heavy alteration under the influence of massive upstream cascade reservoirs, and the JPDDA outperforms the other methods in terms of rationality and stability for practical assessments. Thus, the proposed JPDDA method is strongly advised to handle the hydrological alteration and could provide a reasonable reference for ecological operation.

Evaluation of Subdaily Hydrological Regime Alteration Characteristics for Hydro–Photovoltaic Complementary Operation in the Upper Yellow River

The complementary operation of hydropower and photovoltaic power, aimed at meeting real-time demand, has led to frequent adjustments in power generation, causing significant fluctuations in hydrological systems and adversely affecting fish reproduction. The traditional hydrological regime alteration assessment index is based on index of hydrologic alternation (IHA) and mostly focuses on annual and daily runoff alterations. This study proposes a new set of indicators considering the characteristics of subdaily hydrological regime alterations, including magnitude, rate of change, duration, frequency, and timing. Using the hourly outflow from Longyangxia, an analysis of indicator redundancy was conducted. The alteration of the indicators before and after hydropower and photovoltaic operation was then analyzed using the cumulative probability distribution curve. Additionally, a concentration index was introduced to analyze the variations in hydrological impacts during different months. The results show that the hydro–photovoltaic complementary operation changed the subdaily natural flow regime, significantly increasing the rate of flow increase or decrease and the duration, with most indexes increasing by more than 100% compared with the natural flow regime. Furthermore, the concentration values of the indexes for the hydro–photovoltaic complementary operation were less than 10, indicating a more significant impact on the subdaily flow regime throughout the year. This research provides crucial data for mitigating ecological impacts under multi-source complementary scheduling.

Hydrological Regime Alteration Assessment in the Context of WFD 2000/60: A European and Global Review

Although the impact of hydrology on the ecological status of surface water bodies has been highly recognised, the hydrological regime alteration assessment has proven to be a challenging task. In this context, an extensive structured review analysis was used as a research method to investigate the strength and limitations of the hydrological regime alteration assessment methods as adopted by each member of the European Environment Agency and the cooperating countries, according to the Water Framework Directive 2000/60, as well as to propose future directions. The review was also widened to include the methods currently used worldwide in the hydrological alteration studies and the supporting software tools developed. The implementation of a common methodology on a European scale is not applicable, since a single approach would not be able to cope with the regional needs and conditions. The main limitation in almost all the methods developed by European countries and worldwide is the need for a flow time series of high temporal resolution, so as to also capture the systems’ extreme high and low flows. Automatic monitoring systems for rivers can provide a solution. Additionally, hydrological modelling may provide the necessary data for the definition of the reference conditions. Nevertheless, the main limitations of the methodologies reviewed and the challenge for future development are the incorporation of the groundwater contribution to the hydrological regime and the development of quantitative relationships between flow alteration and ecological response.

Comprehensive evaluation of watershed ecohydrological risk and ecohydrological satisfaction characteristics from the perspective of hydrological variability

Abstract This study quantifies the degree of hydrological regime alteration in the middle and lower reaches of the Yangtze River (MLYR) by incorporating the indicators of hydrologic alteration (IHA) along with six additional indicators. The ecohydrological risks are analyzed using the eco-surplus and eco-deficit indicators. Furthermore, the ecohydrological satisfaction index (ESI) is proposed to characterize the degree to which hydrological conditions meet the eco-water demand of rivers. The results indicate that the concentration period is delayed, and the complexity of hydrological processes is increased in the MLYR. Regarding the variability of hydrological conditions, except for Datong station with a change degree below 0.5, the other stations have experienced high changes. At the annual scale, the eco-surplus and eco-deficit of the MLYR basin have changed with the alteration degree of 0.41 and 0.37, respectively, and the eco-deficit of the mainstream exceeds the eco-surplus, indicating high ecohydrological risks. The ESI at Yichang station has significantly decreased, with the most pronounced decrease occurring in February (−0.35). The ESI of tributaries in the MLYR remains stable, with periods when the ESI at Huangzhuang station exceeds 0.8 accounting for more than 80% of the period from 2004 to 2021.

Современное состояние гидролесомелиоративных систем в лесном фонде Беларуси в условиях изменяющегося климата

The paper presents the results of inventory of drained peatlands and survey of hydroforest-reclamation systems that were transferred to the forest fund after the termination of agricultural and industrial enterprises. It has been established that currently the majority of hydro-forest-reclamation systems in the forest fund of the Republic of Belarus are inoperative and represent swampy and naturally overgrown territory with trees and shrub vegetation. The problem is indicated in reduction of volumes or complete cessation of economic activity on the territory of the entire forest ameliorative fund of Belarus on maintenance of hydromeliorative objects. It is shown that for the period of 2008–2018, 1550,7 ha of peat areas withdrawn from agricultural turnover and 4444,5 ha of depleted peat areas from industrial enterprises were transferred. The Strategy and Scheme of sustainable use of lands with altered hydrological regime within the forest fund of the Ministry of Forestry of the Republic of Belarus were developed.

Reservoir operation impacts on streamflow and sediment dynamics in the transboundary river basin, Vietnam

AbstractHuman interventions activities around the world, particularly reservoir operation, have dramatically altered hydrological and sediment regimes in most of the major river basins. In the Mekong River, specifically the Upper Srepok River Basin (USRB) which is a main tributary of the river basin connected to the Mekong Delta's rice bowl and the Tonle Sap Lake's top inland fisheries, there are increasing concerns about the impacts of cascade reservoir operations on downstream streamflow and sediment budgets. Previous studies estimating impacts either relied solely on observed data or did not verify simulations of regulated streamflow. Using a process‐based hydrological model calibrated and validated for both natural and regulated streamflow in the USRB, it was found that the monthly hydrological changes were up to ±20% compared to pre‐dam periods at the most downstream station bordering between Vietnam and Cambodia (i.e., Ban Don station). The basin also experienced a slight decrease (less than 2%) in annual streamflow. Additionally, average and peak suspended sediment concentration decreased significantly in both of the annual and seasonal periods. At the Ban Don station, sediment loads were reduced 140 thousand tons/year (i.e., 15%) compared to pre‐dam period. Most of the changes in streamflow and sediment budgets in the basin were driven by the Buon Tua Srah reservoir, which had the highest degree of regulation in the basin. Therefore, integrated and transboundary water and sediment management, particularly at Buon Tua Srah reservoir, needs to be developed for the sustainability of the river basin.

Evaluation of reservoir-induced ecological flow with consideration of ecological responses to multiple hydrological alterations: A case study in the Feiyun River Basin, China

With rapid economic and social development, human activities, such as the construction of reservoirs, have satisfied many needs. However, these activities have also caused changes in the hydrological ecosystem of the basin, impacting river biodiversity. The establishment of the Shanxi Reservoir within the Feiyun River Basin has inevitably altered the hydrological system, which was previously shaped primarily by precipitation. This study comprehensively evaluates the impact of Shanxi Reservoir on the hydrological alteration of the basin. Two ecological flow indicators, ecosurplus and ecodeficit, were used based on flow duration curves, along with the Shannon Index of river biodiversity (SI) and several hydrological indicators: the Indicator of Hydrological Alteration (IHA), the Degree of Integrated Hydrological Alteration (D0), and the Dundee Hydrological Regime Alteration Method (DHRAM). The results of the study show that: (1) the previously observed correlation between ecological flow and precipitation was disrupted following the construction of the reservoir. As a result, there was a notable ecological deficit in the spring season, with a maximum of 0.43, and a considerable increase in ecological surplus during winter, reaching a maximum of 4.80. (2) The flow regime of the river has undergone significant changes, resulting in a combined hydrological variability of 66. 44% and an ecological hazard level of 4. This indicates a high risk to the river’s ecological environment. (3) The total seasonal ecological surplus has increased and remained consistently high, which has contributed to a decline in the SI of river biodiversity, the river's biology has degraded over time (4) The use of ecological flow indicators is closely tied to IHA32 indicators. Combining ecological flow indicators with ERHIs has shown to be a successful approach for assessing ecohydrological regimes. These findings have significant implications for future studies in similar cases and offer valuable guidance for managing water resources.

Strategic siting and design of dams minimizes impacts on seasonal floodplain inundation

Dams and reservoirs aid economic development but also create significant negative impacts. Dams fragment rivers and reduce longitudinal connectivity on a network scale. However, dams may also alter discharge regimes and flood peaks, consequently reducing floodplain inundation and lateral channel floodplain connectivity, which impacts floodplain associated ecosystems. Strategic planning has emerged as a promising approach to find a balance between dam impacts and benefits. Yet, strategic planning has predominantly focused on longitudinal connectivity due to the difficulty of including the complex interactions between dam design and operations, hydrologic regime alteration, and the hydrodynamic processes controlling downstream flood extent. Here, we present how to reduce conflicts between hydropower development and loss of floodplain inundation extent by jointly optimizing siting and design of many dams in a data scarce basin. We deploy a coupled hydrological—hydraulic simulation model linked to a multiobjective optimization framework to find development options with the least trade-offs between power generation and downstream impacts on floodplains. Our results for the Pungwe Basin in Mozambique indicate that whilst portfolios of many small storage and run-of-river diversion hydropower plants might create less impacts on the downstream floodplains, installation of some large storage dams would be necessary to attain higher levels of hydropower generation.

Accelerating environmental flow implementation to bend the curve of global freshwater biodiversity loss

Environmental flows (e-flows) aim to mitigate the threat of altered hydrological regimes in river systems and connected waterbodies and are an important component of integrated strategies to address multiple threats to freshwater biodiversity. Expanding and accelerating implementation of e-flows can support river conservation and help to restore the biodiversity and resilience of hydrologically altered and water-stressed rivers and connected freshwater ecosystems. While there have been significant developments in e-flow science, assessment, and societal acceptance, implementation of e-flows within water resource management has been slower than required and geographically uneven. This review explores critical factors that enable successful e-flow implementation and biodiversity outcomes in particular, drawing on 13 case studies and the literature. It presents e-flow implementation as an adaptive management cycle enabled by 10 factors: legislation and governance, financial and human resourcing, stakeholder engagement and co-production of knowledge, collaborative monitoring of ecological and social-economic outcomes, capacity training and research, exploration of trade-offs among water users, removing or retrofitting water infrastructure to facilitate e-flows and connectivity, and adaptation to climate change. Recognising that there may be barriers and limitations to the full and effective enablement of each factor, the authors have identified corresponding options and generalizable recommendations for actions to overcome prominent constraints, drawing on the case studies and wider literature. The urgency of addressing flow-related freshwater biodiversity loss demands collaborative networks to train and empower a new generation of e-flow practitioners equipped with the latest tools and insights to lead adaptive environmental water management globally. Mainstreaming e-flows within conservation planning, integrated water resource management, river restoration strategies, and adaptations to climate change is imperative. The policy drivers and associated funding commitments of the Kunming–Montreal Global Biodiversity Framework offer crucial opportunities to achieve the human benefits contributed by e-flows as nature-based solutions, such as flood risk management, floodplain fisheries restoration, and increased river resilience to climate change.

Identification of Abandoned Logging Roads in Point Reyes National Seashore

Temporary roads are often placed in mountainous regions for logging purposes but then never decommissioned and removed. These abandoned forest roads often have unwanted environmental consequences. They can lead to altered hydrological regimes, excess erosion, and mass wasting events. These events can affect sediment budgets in streams, with negative consequences for anadromous fish populations. Maps of these roads are frequently non-existent; therefore, methods need to be created to identify and locate these roads for decommissioning. Abandoned logging roads in the Point Reyes National Seashore in California, an area partially under heavy forest canopy, were mapped using object-based image processing in concert with machine learning. High-resolution Q1 LiDAR point clouds from 2019 were used to create a bare earth model of the region, from which a slope model was derived. This slope model was then subjected to segmentation algorithms to identify and isolate regions of differing slopes. Regions of differing slopes were then used in a convolutional neural network (CNN), and a maximum likelihood classifier was used to delineate the historic road network. The accuracy assessment was conducted using historic aerial photos of the state of the region post-logging, along with ground surveys to verify the presence of logging roads in areas of question. This method was successfully able to identify road networks with a precision of 0.991 and an accuracy of 0.992. It was also found that the CNN was able to identify areas of highest disturbance to the slope gradient. This methodology is a valuable tool for decision makers who need to identify areas of high disturbance in order to mitigate adverse effects.

Secretive marsh bird occupancy across a spectrum of hydroelectric reservoir management in western montane Canada

AbstractDam construction projects have created opportunities for water security, targeted flood protection, and energy production but at the cost of increasing anthropogenic pressure on affected aquatic ecosystems. Wetland ecosystems are often among the most vulnerable, as underlying hydrological regimes influence overall wetland structure and function. Marsh bird species are wetland and riparian habitat specialists, many of which are experiencing population declines across North America. We examined how the alteration of hydrological regimes for generating hydroelectric power affected the occurrence of secretive marsh bird species in the western montane region of British Columbia, Canada. We established survey stations in wetlands across 2 regions, the West Kootenay and the Columbia Wetlands, sampling across a spectrum of hydrological regimes and other potentially relevant factors. At each station, we assessed wetland occupancy during the breeding season using broadcast‐callback surveys focused on 5 secretive marsh bird species: American bittern (Botaurus lentiginosus), American coot (Fulica americana), pied‐billed grebe (Podilymbus podiceps), sora (Porzana carolina), and Virginia rail (Rallus limicola). Additionally, we measured vegetation structure and the proximity and size of nearby water bodies for each survey station. We then used occupancy models to assess important correlates behind wetland occupancy for these marsh bird species, considering water management operations, regional differences, and local‐ and landscape‐level wetland characteristics. Secretive marsh bird species were more likely to occupy wetlands in areas with less frequently altered hydrological regimes. Occupancy models highlighted local‐ and landscape‐level characteristics as important correlates for wetland occupancy by marsh birds. Wetlands with frequently altered hydrological regimes had more open water cover and less tall vegetation present, conditions that were negatively associated with occupancy. Altered wetlands in this study were farther from the next nearest wetland, which was also negatively associated with occupancy. We suggest reservoir management is altering vegetation communities within these wetlands, indirectly promoting lower occupancy of secretive marsh bird species.

Are flood events really increasing? A case study of Krishna River Basin, India

There is a heightened sensitivity about the risks posed by the prospect of climate change as deduced from the results of the global-regional climate models. Notwithstanding the moderating, albeit feebly articulated, acknowledgement of variability as being an intrinsic attribute of climate, it is often claimed that intensification of large hydrological extremes such as floods is indeed emerging as a new looming reality. This has aptly given rise to fears of prospective exacerbated socio-economic vulnerability. In an attempt to investigate the veracity of whether the hydrological flood events are really intensifying across the Krishna River Basin, the present study has examined the historical floods in Krishna River Basin (KRB) using available streamflow and precipitation records along with published reports and featured news articles. The approach followed is based on quantitative and qualitative analysis of floods in KRB at the subsystem scale (K1 to K12). The quantitative analysis involved i) Development of unregulated flow series through hydrological modelling, ii) Frequency analysis of unregulated flows and precipitation, iii) Threshold selection for defining the small, medium, and large floods, iv) Identification of flood events in observed streamflow series and v) Identification of causal rainfall and its relationship with flood peak. The qualitative analysis focused on published reports and news articles to attempt a multivariate characterization of flood flow attributes and the accompanying losses. The study concludes that the hypothesis that flood events are intensifying is untenable for most subsystems of KRB except K7 (Lower Krishna Basin) being the sole exception where, in sharp contrast, flood events show signs of moderation. Interestingly, cyclic patterns analogous to Noah and Joseph Effect are seen in the case of small floods for all the subsystems except K7. Non-recurrent, standalone extremes that bear the classical signature of Erratic Noah and Joseph elements have also been observed in medium and large floods in all the subsystems except the K12 subbasin (Munneru Basin). The study confirms that qualitative analysis alone cannot lead to an incontrovertible determination of trend like features in flood records as every event in the historical record bears a unique multi-dimensional footprint arising from a mix flood characteristics, associated losses and perceived short and long-term impacts. This study can provide a guideline to identify changes in flood typology especially in basins with altered hydrologic regimes and serve as an aid in planning and formulating policies for ameliorative flood management strategies as well as in policy restructuring when deemed to be necessary.

Settlement suitability analysis of a riverine floodplain in the perspective of GIS-based multicriteria decision analysis

Riverine floodplains are highly dynamic and the most vulnerable space on Earth particularly in flat alluvial plains of major river systems. Suitable site selection for sustainable human settlements in active floodplain areas is a critical task for decision-makers in terms of quality of lithology, ecologically fragile landmass, climate-induced hazards, immense population pressure, and environmental conservation issues. This research introduces a methodology for settlement suitability zone (SSZ) that employs GIS-based multi-criteria decision-making (MCDM) techniques. As a case study, an altered hydrological regime of the lower Ganga riparian zone was chosen to identify the SSZ as these areas are the most susceptible to riverine hazards. Twelve significant variables reflecting on topography, climate, landscape, and environment have been selected in the multi-criteria evaluation platform. The CRiteria Importance Through Intercriteria Correlation (CRITIC) method is adopted to specify the weights of the criteria and utilize an inverse distance-weighted (IDW) spatial interpolation technique to generate an SSZ map in a GIS environment. The study zone is spatially quantified into five categories, from unsuitable to high-suitable with a natural breaks (Jenks) classification method. Subsequently, the final results are validated through a receiver operating characteristics (ROC) curve using randomly selected 56 hazard-exposed location points. The outcome revealed that 8.45% of the riparian area falls under unsuitable, 21.87% under low-suitable, and 33.27% under moderate-suitable for locating human settlements. The generally suitable and high-suitable categories account for 36.40% of the total study zone. A spatial sensitivity analysis is also applied to gauge the influence of each parameter on the MCDM outcomes. The SSZ mapping results from this study can help local authorities to plan for sustainable settlement development in environmentally fragile areas.

Evaluation of hydrological regime alteration and ecological effects in the upper reaches of the Yangtze River, China

Abstract The state of water flow is recognized as a key driver of the structure and function of river ecosystems. We selected streamflow data (1960–2020) from three key hydrological stations in the upper Yangtze River: Pingshan, Cuntan, and Yichang. We analyzed the characteristics and changes of the hydrologic regimes of the Yangtze River using the Mann–Kendall method, wavelet analysis, and the IHA-RVA method, and explored the response mechanisms of fish to changes in the hydrological regimes. The results show that (1) the average annual discharge of the upper reaches of the Yangtze River is decreasing, and the abrupt changes in Pingshan, Cuntan, and Yichang stations occurred in 1985, 1998, and 2002, respectively, with the main period of 24–32 years. (2) The overall degree of hydrological changes at Pingshan, Cuntan, and Yichang stations is 45%, 50%, and 61%, respectively, all of which are moderate changes. (3) Dams in the upper reaches of the Yangtze River have caused changes in the flow regime of the Yangtze River. Among them, the changes in the alternating frequency of flow and the annual extreme flow have affected the habitat of aquatic organisms and seriously affected the reproduction of important fishes in the Yangtze River.

Assessment of future eco-hydrological regime and uncertainty under climate changes over an alpine region

The source region of the Yellow River Basin (SYRB) is an alpine region sensitive to climate changes. As global climate change intensifies, it is essential to explore the future hydrological regime alteration and its ecological effects on the basin to provide evidence for water resources management and ecological restoration in the area. This study offers a framework for assessing the future multi-dimensional hydrological regime alteration and its ecological effects. Selected from Global Climate Models (GCMs) that performed well in the Sixth Coupled Model Intercomparison Project (CMIP6), the VIC model was forced by the GCMs after downscaling and bias-correction. Then the hydrological regime alteration and potential ecological effects in the region under SSP126, SSP245, SSP585 future scenarios were systematically assessed by the IHA-RVA system, and the contribution of different uncertainty sources was quantified through the two-way ANOVA. The results indicated that: (1) The temperature and precipitation will increase in the future under all scenarios, while the runoff tends to show a downward trend. By 2015–2100, the flow under SSP126, SSP245 and SSP585 scenarios may vary from −44.7 to 13.0 %, −48.7 to 2.43 %, −53.7 to 4.0 %, respectively, when compared to the reference period (1961–1990). (2) Moderate alterations with RVA = 33 % will be observed in the hydrological regime in the basin under SSP245 and SSP585 scenarios, and low alterations with RVA = 26.7 % under the SSP126 scenario. The spring discharge of the basin will decrease significantly, and the annual extreme flow is projected to decrease, but the frequency of drought and flood events will tend to increase. (3) There are multiple sources of uncertainty in predicting the future hydrological regime in the SYRB. The uncertainty due to the climate model is the dominant factor, followed by the interaction between emission scenarios and the climate model, and the average contribution to uncertainty of them is 69.5 % and 20.8 % respectively. The uncertainty of emission scenarios is mainly reflected in winter flow, while the climate model mainly affects the summer flow and annual maximum flow, and the uncertainty of interaction between them varies in different periods.