Indicators Of Hydrologic Alteration Research Articles

Assessing the effects of dam regulation on multiscale variations in river hydrological regime and ecological responses

ABSTRACT Using a combination of the long short-term memory model and hydrological change indicators, this study proposes an assessment framework at inter-annual and intra-annual scales to quantify the hydrological regime changes and ecological event responses caused by the regulation of the Three Gorges Dam (TGD) in the upper reaches of the Yangtze River. The results indicate that during the post-TGD period (2004–2019), 2 indicators of the natural flow regime undergo a high degree of alteration at the inter-annual scale, which increase to 12 when regulated flows are considered. Furthermore, we find that while climate and incoming water change significantly reduces the annual flow and monthly flow during the flood season, it increases the complexity (79%) and ecodeficit at the seasonal scale (94%). Among the 32 indicators of hydrologic alteration, TGD is the dominant factor influencing changes in 20 indicators, increasing the magnitude of low-flow events, decreasing the frequency of high-flow pulses, and advancing the timing of 1-day minimum flow (43 Julian date). From the hydrological perspective, the altered rising water conditions due to TGD regulation may cause an average decrease of 19.5% in the fry abundance for the Four Famous Major Carps.

How does the daily regulation hydropower station reduce the hydrological regime impact? A case study in upper Yellow River

ABSTRACT The regulation of hydropower stations has profoundly altered river flow patterns. While studies have extensively assessed the impact of large or multiyear regulated hydropower stations on hydrological regimes using indicators of hydrological alteration (IHA) and range of variability approach (RVA), the impact of daily regulation hydropower stations has received comparatively less attention. This study aims to evaluate the influence of daily regulation hydropower stations on hydrological regime changes. The analysis focuses on the upper Yellow River region in China, which houses cascade hydropower stations, utilizing daily runoff data from the Guide hydrological station spanning from 1954 to 2020. The Mann–Kendall test revealed 27 of 32 IHAs with a significant trend when considering the operation of the multiyear regulated hydropower station (Longyangxia). However, this number decreased to 18 IHAs when daily regulation hydropower stations (Laxiwa and Nina) were included. Evaluation using the RVA method indicated that only 46.87% of IHAs showed high alterations from the natural regime when considering the operation of daily regulation hydropower stations, a decrease from 75.00% when solely considering Longyangxia. Findings suggest that daily regulation hydropower stations can effectively mitigate the adverse effects of multiyear regulated hydropower stations, bringing the hydrological regime closer to a natural state.

Assessment of hydrological baseline condition and its alteration in Athabasca River Basin, Canada

Study regionAthabasca River Basin (ARB), Canada. Study focusThis study aimed to characterize the flow regime of the ARB, a basin with diverse hydroclimatic and geological characteristics. Forty-two different flow indicators from the Indicators of Hydrological Alteration (IHA) and Cold regions Hydrological Indicators of Change (CHIC) were employed. The natural range of these indicators was established for the baseline period (1961–1990), and subsequent alterations during the recent period (1991–2020) were systematically examined. Principal Component Analysis (PCA) was applied to identify pivotal indicators shaping the basin's flow regime. In addition, trends of key indicators were examined at eight distinct locations within the basin. New hydrological insights for the study regionThe findings indicate spatiotemporal variation between the basin's upper and lower parts. The upstream region exhibited an earlier peak flow (9 days), an earlier ice break-up (17 days), and a shorter ice cover duration (22 days) compared to the downstream region. Increased winter and spring flow have led to an augmentation of annual flow by 3.8 % in the upper region. In contrast, downstream flow experienced a decline throughout the year (11.38 %), which was found to be statistically significant at a rate of 3.24 m3/s/year. Alteration analysis revealed a shift toward the 'low category' (below their defined baseline range) for most indicators in the recent period, underscoring a transition towards a diminishing flow regime, with an overall alteration ranging at low to moderate levels (19–38 %). Late summer flow reduction (8–25 %) can have critical implications, given the rising water demand in the basin. The study identified eleven key indicators encapsulating the basin's flow regime variability range. It was found that ice cover, its break-up, and spring freshet significantly influence the flow regime of the basin. The findings from this study will assist decision-makers in making more informed decisions for the holistic management of water resources in the basin.

Unveiling hydrological dynamics in data-scarce regions: experiences from the Ethiopian Rift Valley Lakes Basin

Abstract. The hydrological system of the Rift Valley Lakes in Ethiopia has recently experienced changes over the past 2 decades. Potential causes for these changes include anthropogenic, hydro-climatic, and geological factors. The main objective of this study was to utilize an integrated methodology to gain a comprehensive understanding of the hydrological systems and potential driving factors within a complex and data-scarce region. To this end, we integrated a hydrologic model, change point analysis, indicators of hydrological alteration (IHA), and a bathymetry survey to investigate hydrological dynamics and potential causes. A hydrologic model (the Soil and Water Assessment Tool Plus, SWAT+) was parameterized for the gauged watersheds and extended to the ungauged watersheds using multi-site regionalization techniques. The SWAT+ model performed very well to satisfactorily for daily streamflow in all watersheds with respect to the objective functions of the Kling–Gupta efficiency (KGE), the Nash–Sutcliffe efficiency (NSE), and percent bias (PBIAS). The findings reveal notable changes in lake inflows and lake levels over the past 2 decades. Lake Chamo experienced an increase in area of 30.1 km2 (9.5 %), an increase in depth of 4.4 m (30.9 %), and an increase in volume of 7.8×108 m3 (27.2 %). In contrast, Lake Abijata witnessed an extraordinary 68 % decrease in area and a depth decrease of 1.6 m (37.2 %). During the impact period, the mean annual rainfall experienced a decrease of 6.5 % and 2.7 % over Lake Abijata and Lake Chamo, respectively. Actual evapotranspiration decreased by 2.9 % in Lake Abijata but increased by up to 4.5 % in Lake Chamo. Surface inflow to Lake Abijata decreased by 12.5 %, while Lake Chamo experienced an 80.5 % increase in surface inflow. Sediment depth in Lake Chamo also increased by 0.6 m (4.2 %). The results highlight that the changing hydrological regime in Lake Chamo is driven by increased surface runoff and sediment intrusion associated with anthropogenic influences. The hydrological regime of Lake Abijata is affected by water abstraction from feeding rivers and lakes for industrial and irrigation purposes. This integrated methodology provides a holistic understanding of complex data-scarce hydrological systems and potential driving factors in the Rift Valley Lakes in Ethiopia, which could have global applicability.

Assessment of land use/ land cover change derived catchment hydrologic response: An integrated parsimonious hydrological modeling and alteration analysis based approach

Land use/land cover (LULC) change, often a consequence of natural or anthropogenic drivers, plays a decisive role in governing global catchment dynamics, and subsequent impact on regional hydrology. Insight into the complex relationship between the drivers of LULC change and catchment hydrology is of utmost importance to decision makers. Contemplating the dynamic rainfall-runoff response of the Indian catchments, this study proposes an integrated modeling-based approach to identify the drivers and relative contribution to catchment hydrology. The proposed approach was evaluated in the tropical climate Nagavali River Basin (NRB) (9512 km2) of India. The Soil and Water Assessment Tool (SWAT) hydrological model, which uses daily-scale rainfall, temperature, wind speed, relative humidity, solar radiation, and streamflow information was integrated with the Indicators of Hydrologic Alteration (IHA) technique to characterize the plausible changes in the flow regime of the NRB. Subsequently, the Partial Least Squares Regression (PLSR) based modeling analysis was performed to quantify the relative contribution of individual LULC components on the catchment water balance. The outcomes of the study revealed that forest land has been significantly converted to agricultural land (45–59%) across the NRB resulting in mean annual streamflow increase of 3.57 m3/s during the monsoon season. The affinity between land use class and streamflow revealed that barren land (CN = 83–87) exhibits the maximum positive response to streamflow followed by the built-up land (CN = 89–91) and fallow land (CN = 88–93). The period 1985–1995 experienced an increased ET scenario (911–1050 mm), while the recent period (2005–2020) experienced reduced ET scenario owing to conversion of forest to agricultural land. Certainly, the study endorses adopting the developed methodology for understanding the complex land use and catchment-scale hydrologic interactions across global-scales for early watershed management planning.

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 holistic approach to projecting streamflow and analyzing changes in ecologically relevant hydrological indicators under climate and land use/cover change

Understanding streamflow change and its ecological impacts under climate change and land use/cover change (LUCC) makes possible the improvement of water and ecological governance decision-making. Gaining a comprehensive understanding of the drivers of historical streamflow changes can provide valuable insights for effective projections of future streamflow. Meanwhile, future changes in ecologically relevant hydrological indicators need more attention to maintain the ecological stability of rivers. This study has developed a holistic framework based on a physically based model (the Variable Infiltration Capacity model, or VIC) and the indicators of hydrological alteration (IHA) method to decouple the drivers of historical streamflow change and to project changes in future streamflow and ecologically relevant hydrologic indicators. The proposed framework was applied in the upper Han River basin (UHRB), which is the water source for the water diversion project in China. The results showed that climate change contributed 99.67 % of the streamflow decrease in the 1980–1990s and 108.21 % and 102.09 % of the streamflow increase in the 1990–2000s and 2000–2010s respectively. LUCC had a weak impact on streamflow in these three periods. Projected climate change will further exacerbate streamflow change. The projected monthly streamflow is expected to increase from October to December. The counts of streamflow pulses are expected to decrease, but the duration of each high pulse will increase. These changes will cause stress in floodplain vegetation, alterations to stream chemistry, reductions in fish diversity (decreased streamflow pulses), and alterations to river landscape and animal habitat (increased flood duration). The developed framework is expected to provide significant technical guidance for water resource management and river conservation.

Assessment of Climate Change Effects of Drought Conditions Using the Soil and Water Assessment Tool

A combination of annual peak water demand due to seasonal population spikes along with small and shallow aquifers has prompted an assessment of the region’s watersheds as operating at a net water deficit. This study uses the Soil and Water Assessment Tool (SWAT) to simulate historical drought conditions in the Chipuxet watershed in Rhode Island, USA. The calibrated and validated model uses the Soil Moisture Deficit Index (SMDI) and Evapotranspiration Deficit Index (ETDI) as well as an Indicators of Hydrological Alteration (IHA) calculation to determine the frequency and severity of historical droughts and to simulate climate change conditions developed through a downscaled climate model selection. The output data for the historical and climate change scenarios were analyzed for drought frequency and severity. Results indicate that water stress will increase in both low-emission (RCP4.5) and high-emission (RCP8.5) scenarios. Additionally, the SMDI and ETDI show that RCP8.5 climate scenarios will have more severe deficits. Finally, IHA data indicate that zero-flow days and low-flow durations increase under all climate scenarios.

Evaluation of extreme flow characteristics in the Casamance watershed upstream of Kolda using the IHA/RVA method

Understanding water availability is essential for the development and management of water resources, as well as for designing interventions for river health. Climate change/variability impacts the hydrology of a river system, which subsequently affects human and ecological health by altering the structure and function of the aquatic ecosystem. This study therefore aims to assess water availability and river health according to current and future climate scenarios in the Casamance watershed upstream of Kolda. Climate change is expected to increase hydrologic alterations from low (currently) to high (in the future), as revealed by the Indicators of Hydrologic Alteration (IHA) tool. Average annual water availability decreased, varying seasonally, and seasonal trends followed annual trends under Shared Socioeconomic Pathways (SSP) scenarios. In the basin, negative developments in minimum and maximum annual conditions are generally decreasing over the future period, compared to the reference period (1985-2014), with the exception of the minimum flow rate over 7 and 30 days on SSP 126 and the minimum flow rate over 30 days and the maximum flow rate 1, 3 and 7 days on SSP 585. In this SSP 585 scenario, the Mann Kendall test on the minimum flow rate and the flow rate maximum indicate the most significant downward trend with a risk of error of 0.05, with a Kendall tau varying from -0.45 m3/s/year to - 0.05 m3/s/year. For the minimum flow parameters, Kolda station shows negative Hydrological Alteration (HA) values for the high RVA category, which results in a decrease in low flow.

Evaluating indicators of hydrologic alteration to demonstrate the impact of open-pit lignite mining on the flow regimes of small and medium-sized rivers

Our study provides a retrospective evaluation of the perturbances of the opencast mining on the small river. Based on a standard 'before-after-control-impact' approach, we assess the impact of disturbances on aquatic ecosystems. For this purpose, we used IHA (Index of Hydrological Alteration) statistics to fully quantify the impact of open-pit mine on flow regimes of small-to-medium-size rivers. The analysis results in flow data captured in the 33 parameters of the range variability approach (RVA) and five ecological flow components (EFC). This approach helped us comprehensively evaluate the alteration in the flow regime in areas of open-pit mining on the example of the Noteć River, a typical lowland river. We conclude that the level integrated hydrologic alterations to this river under the influence of the groundwater depression cone and water from the mine dewatering are high, as assessed by the RVA and EFC methods. Specifically, this work uses the IHA framework to verify the necessity of including a specific group of indicators. Our analysis shows that for the post-impact period on the investigated river, the functioning of the river ecosystem was degraded. One of the EFC components completely disappeared at both water gauge stations. There were also profound hydrologic alterations, such as increased frequency or duration of “extreme low flows” at one station; at the second station, “high flow pulses” occurred more frequently. More than 65 % of the altered parameters in five IHA groups were modified drastically. In the river section affected by the groundwater depression cone, both the minimum and maximum flows decreased by 20 % to 55 %. In the section where water from the mine dewatering is fed in, the minimum flows changed by + 170 to + 230 %. The use of the IHA tool provides an opportunity for environmental flow restoration of water conditions in degraded post-mining areas.

Separating climate change and human activities' effects on flow regime with hydrological model error correction

Climate change and human activities have markedly altered flow regimes, leading to deleterious consequences for riverine ecosystems. The widely employed hydrological modeling restoration method for conducting flow regime attribution often tends to underemphasize the impact of simulation errors on attribution outcomes. Moreover, the issue of ambiguous attribution targets in flow regime attribution remains a critical concern. This study presented a flow regime attribution framework integrated the hydrological model error correction. Indicators of hydrologic alteration (IHA) simulated by the XAJ and GR4J hydrological models and corrected using the quantile-mapping (QM) and convolutional neural network-long short term memory (CNN-LSTM) error correction methods, were employed to create 6 scenarios for assessing the impacts of climate change and human activities on flow regime changes. A case study was conducted in the Xitiaoxi basin, located in the upper reaches of Lake Tai in China. The results demonstrated that CNN-LSTM's superior performance over QM in correcting IHA metrics simulated by both XAJ and GR4J. The mean flow regime attribution results obtained from XAJ and GR4J simulations following the application of CNN-LSTM correction, mitigated the underestimation of contributions from the primary driving factors, in contrast to uncorrected or QM-corrected IHA metrics attribution results. Additionally, the regime attribution findings revealed all 33 IHA metrics experienced changes, with 73 % of them attributing human activities as the predominant driving forces. Substantial variations in IHA metrics exerted a certain degree of pressure on riverine habitats, particularly impacting the spawning and reproductive activities of piscine species.

Evaluating Effects of Terraces on Flow Regimes in a Hilly and Mountainous Basin

Terraces play a crucial role in regulating the water cycle. The management and restoration of, and the conservation strategies and plans for basins rely heavily on the assessment of alterations in hydrological characteristics, whether natural or man-made, within these basin systems. This study centers on evaluating the impact of terraces on temporal variations in the hydrological regime within the Laixi River basin, within the context of climate variability. To achieve this, we employed a hydrological model and applied the Indicators of Hydrologic Alteration and Range of Variability Approach (IHA–RVA). The results show that, under the influence of terraces, the annual flow exhibited an overall decreasing trend. There was a noticeable decrease in streamflow from March to July, while from October to December, there was a clear upward trend, with increases ranging from 4.76% to 8.10% at the Guanshenxindi (GSXD) and Watershed outlet (WO) cross-sections. The indicators related to the minimum flow showed an overall increasing trend, whereas all indicators related to the maximum flow exhibited a clear decreasing trend. Both high and low flow pulse counts decreased, while high and low pulse durations increased overall. The overall trend of flow reversal counts also showed a decrease. All hydrological indicators exhibited low levels of alteration, with hydrologic alteration values lower than 33.33%. However, the influence of terraces on the upstream hydrological conditions was more pronounced than their downstream effect. The terraces in the study area have played a beneficial role in the flood regulation, drought mitigation, and water resource conservation of the Laixi River. They have contributed to stabilizing the daily average flow during high flow periods and have had a positive impact on the ecological base flow during low flow periods, thereby improving the aquatic ecological environment. This study provides theoretical support for river regulation within the framework of soil and water conservation measures.

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.

Climate change potentially induces ecological change in the Ethiopian Rift Valley Lakes Basin

Streamflow regime management is critical for preserving species in riverine and riparian habitats. Quantifying flow-ecology relationships can help to characterize the effect of flow regime change on species; however, dealing with this in ungauged catchments is challenging. By regionalizing simulation of streamflow to ungauged catchments, the Indicators of Hydrological Alterations (IHA) are calculated and used as a proxy for quantifying ecological impacts. High-resolution Regional Climate Models are used to derive the future streamflow in both gauged and ungauged catchments of the Ethiopian Rift Valley Lakes Basin (RVLB). Consequently, 32 IHAs representing the magnitude, duration, frequency, rate, and timing of streamflow events during their historical and future periods are calculated. The number of cases for future IHAs deviating from their historical range is calculated, which is called the non-attainment rate of future IHAs. A threshold value for the non-attainment rate is set to classify the impact as no-impact, low, medium, or high. The non-attainment rate for the future period indicates that, high ecological impact resulted in October, which is the local high flow month. Spatially, a shift towards a later date of the Julian date indicating the maximum flow resulted in a high ecological impact. This approach can be adapted to other regions with reliable regionalization results and suitable future climate models, which would be useful for the quantification and management of ecological impacts in ungauged regions.

Evolution of Hydrological Conditions and Driving Factors Analysis of the Yongding River in a Changing Environment: A Case Study of the Xiangshuipu Section

Hydrological conditions are key factors in the evaluation of water resources and ecosystems. The Yongding River Basin has many irrigated areas, and excessive agricultural water consumption has led to serious water shortages and ecosystem damage. To investigate the evolution of ecohydrological conditions and their driving factors in the Yongding River basin in a changing environment, this study combines indicators of hydrologic alteration with the range of variability approach (IHA-RVA) to identify the most ecologically relevant hydrological indicators (ERHIs) and to determine the periods of hydrological variability in the basin, using the Xiangshuipu section on the Yang River as the study area. By calculating the degree of hydrological alteration, the evolutionary pattern of ecohydrological conditions in the basin was analyzed, and the WetSpa model was used to quantitatively identify the contributions of climate change, reservoir storage, and irrigation water withdrawal to the alteration of hydrological conditions. The results showed that the rise and fall rate; maximum and minimum 1 day flows; dates of maximum flow; and July flows were the most ecologically relevant hydrological indicators for the Xiangshuipu section. Variability of this section occurred between 1982 and 1988; except for the annual maximum 1 day flows and fall rate, which underwent moderate changes; all other indicators exhibited small changes and the overall hydrological alteration of the Xiangshuipu section was low. The most influential change in the hydrological conditions was irrigation water withdrawal (from specific irrigation); followed by climate change and reservoir storage. The results of this study provide an important basis for water resources utilization and ecological management in the Yongding River basin.

Projected flow regimes and biodiversity changes under climate change in the planning western route source areas of the South-to-North Water Diversion Project

Scientific evaluation of the eco-hydrological regimes is of great significance for water resource management and aquatic ecosystem protection. The paper took the western route source areas (WRSA) of the South-to-North Water Diversion Project (SNWDP) as the research region. In order to quantify climate-induced eco-hydrological effects, a general framework was proposed to predict changes in flow regimes and fluvial biodiversity under climate change: The coupling of Global Climate Models (GCMs) and the Distributed Time Variant Gain Model (DTVGM) was used to simulate discharge under different climate conditions. Based on Indicators of Hydrologic Alteration (IHA), changes in eco-hydrological regimes were evaluated by using the Range of Variability Approach (RVA), assessment of overall hydrological change degree (D0), and Shannon index (SI). Changes in discharge, flow regimes, and fluvial biodiversity of WRSA were analyzed during the projected period (2041–2100) compared to the base period (1960–2014). According to the projections, under four SSPs-RCPs scenarios, the future discharge of WRSA increases significantly compared to the base period. D0 of WRSA is moderately or severely changed, and hydrological changes are mainly reflected in high flows such as monthly median flows during flood season, maximum flows, and high pulse duration. While flow regimes are disturbed, SI values of WRSA keep rising and the biodiversity is improved. The increase of discharge and SI becomes progressively greater with elevated radiation intensity, and the quantity of severely altered indicators of IHA increases. In conclusion, future hydrological alterations in SNWDP are expected to further intensify with higher levels of climate change, and these changes are generally conducive to the improvement of fish biodiversity.

Multi-scale flow regimes and driving forces analysis based on different models: a case study of the Wu River basin

Abstract Quantitatively separating the influence of climate change and human activities on runoff is crucial to achieving sustainable water resource management in watersheds. This study presents a framework for quantitative assessment by integrating the indicators of hydrologic alteration, the whale optimization algorithm and random forest (WOA-RF), and the water erosion prediction (WEP-L) models. This framework quantifies the differences in hydrological conditions and their driving forces at multi-timescales (annual, seasonal, and monthly). The results indicate that the runoff of the Wu River has decreased since 2005. Climate factors were found to influence the interannual variation of runoff mainly. Meanwhile, human activities had a more significant impact in autumn, with a relative contribution rate of 59.0% (WOA-RF model) and 70.8% (WEP-L model). Monthly, the picture is more complex, with the results of the WOA-RF model indicating that climate change has a significant impact in July, August, and September (88.8%, 92.7%, and 79.3%, respectively). However, the WEP-L model results showed that the relative contribution of land use is significant in April, May, June, October, and November (51.24%, 64.23%, 63.63%, 53.16%, and 50.63%, respectively). The results of the study can be helpful for regional water allocation.

Disaggregated monthly SWAT+ model versus daily SWAT+ model for estimating environmental flows in Peninsular Spain

The Water Framework Directive requires all water bodies in EU countries to ensure the ecological integrity of freshwater ecosystems in all water bodies. A “good” status in water bodies leads to their biological elements to reproduce reference conditions, so quantity and timing should be considered in describing environmental flows. However, the availability of daily natural flow data is one of the major drawbacks, especially in highly water-regulated countries, such as Spain, and hydrological models, such as the Soil and Water Assessment Tool (SWAT+) model, can be used to generate them. This work evaluated three different approaches for obtaining daily flows used to characterise the natural regime and to estimate environmental flows in the Piloña River (northern Spain) and Tagus River (centre Spain) basins: Scenario 1) daily flows simulated by the SWAT+ model calibrated on a monthly scale; Scenario 2) daily flows estimated by applying monthly-to-daily disaggregation techniques from the monthly series obtained from the SWAT+ model calibrated on a monthly scale using Water Rights Analysis Package (WRAP) software; and Scenario 3) daily flows simulated by the SWAT+ model calibrated on a daily scale. The Kling–Gupta efficiency (KGE), percent bias (PBIAS), Nash–Sutcliffe efficiency (NSE), root mean square error (RMSE) and standard deviation ratio (RSR) were used to evaluate the model’s performance. Furthermore, the indicators of hydrologic alteration in rivers (IAHRIS) and the basic flow methods were assessed and compared with those obtained directly using the real data observed at the gauging station. Our results indicated that Scenario 2 outperformed the rest of the approaches for all the statistics used. KGE and NSE varied between 0.78 and 0.92 for both basins in Scenario 2 while these values decreased to 0.50–0.60 for KGE and 0.20–0.40 for NSE in Scenarios 1 and 3. Moreover, PBIAS ranged between 3.24 and 4.47% in validation periods in Scenario 2, while it decreased to −14.64% in Scenario 3. Likewise, Scenario 2 was also observed to show better performance related to both the patterns of the natural regime and the basic flow values, which were generally underestimated by the other scenarios. The methodology proposed provides a valuable tool for evaluating and managing the hydrological and environmental status of river basins.

Assessment of hydrological trends and changes in hydroclimatic and land use parameters in a river basin in northeast Brazil

The hydrological effects of land use change are difficult to differentiate when changes are slow and hard to isolate when climate variability is also present. The study aims to evaluate the effects of climate variability and human activity on the flow in the Cachoeira River Basin. For this purpose, classical tests were used to identify trends and measure the strength of association between two variables, as well as the Rainfall Anomaly Index (RAI) and the Budyko Curve Decomposition were applied to the study so that it could verify the behavior of precipitation and the quantification of anthropic impacts and climate variation in the basin. In addition, the Indicators of Hydrologic Alteration (IHA) software was used to identify hydrological changes in the basin as a function of time. The results show a significantly decreasing trend for the forest and a significantly positive trend for pasture class and temperature. Correlation analysis indicated that changes in flow rate are correlated with precipitation, however, anthropic factors must be potentiating the impacts of climate variations as shown in the period 1991–1995 and 2011–2015. Finally, the hydrological indicators of the Cachoeira River Basin showed significant changes, which may compromise the flows in the long term if anthropic factors continue to enhance the climatological factors.

Optimizing environmental flow based on a new optimization model in balancing objectives among river ecology, water supply and power generation in a high-latitude river

Environmental flow plays an important role in maintaining the health of river ecosystems and aquatic habitats. Although ecological regulation of environmental flow has attracted the attention of scientists, managing the world's reservoir-regulated rivers to better meet the needs of human being and ecosystems is a complex social challenge. To address the above issues, we constructed a model for optimizing reservoir operation based on a balance in achieving multi objectives among environmental flow, water supply and power generation (EWP). The model was solved using an intelligent multi-objective optimization algorithm (ARNSGA-III). The developed model was demonstrated in a large reservoir, Laolongkou Reservoir in the Tumen River. The results showed that the reservoir altered environmental flows mainly in terms of flow magnitude, peak, times, duration and frequency, which result in a sharp decrease in spawning fish, and degradation and replacement of vegetation along the channels. In addition, the mutual feedback relationship between the objectives of environmental flows, water supply and power generation is not static, but varies over time and space. The constructed model based on Indicators of Hydrologic Alteration (IHAs) can effectively guarantee the environmental flow at daily scale. In detail, the river ecological benefit increased by 64% in wet year, 68% in normal year, 68% in dry year after optimizing regulation of reservoir, respectively. This study will provide a scientific reference for the optimizing of the management in other rivers affected by dams.