Indicators Of Hydrologic Alteration Research Articles

Nonstationary Ecological Instream Flow and Relevant Causes in the Huai River Basin, China

Based on the daily precipitation data during 1960–2016 at 72 stations and the daily streamflow data during 1956–2016 at 7 hydrological stations in the Huai River Basin (HRB), China, eco-surplus and eco-deficit under influences of abrupt streamflow behaviors were analyzed using Flow Duration Curve (FDC). The relations between indicators of hydrological alteration (IHA) and ecological indicators (Shannon Index, SI) were quantified, investigating impacts of altered hydrological processes on the evaluations of the ecological instream flow. Besides, we also quantified fractional contributions of climatic indices to nonstationary ecological instream flow using the Generalized Additive Models for Location Scale and Shape (GAMLSS) framework. While the possible impact of human activities on ecological instream flow will be revealed based on land use changes data. The results indicated that: (1) FDC is subject to general decrease due to hydrological alterations, and most streamflow components are lower than 25% FDC. We found increased eco-deficit and decreased eco-surplus due to altered hydrological processes. The FDC of the streamflow in the main stream of the HRB is lower than that along the tributaries of the HRB. Eco-surplus (eco-deficit) changes are in good line with precipitation anomaly changes during the Spring, Autumn and Winter periods. However, the hydrological alterations due to hydrological regulations by the reservoirs are the primary cause behind the mismatch between ecological instream flow and precipitation anomalies during summer; (2) Annual and seasonal eco-surplus (eco-deficit) is decreasing (increasing) and that during winter season is an exception. Although higher eco-surplus in winter than in other seasons, the eco-surplus is decreasing persistently and the 21st century witnessed the lowest eco-surplus along the main stream of the HRB. Meanwhile, the Shannon index indicated decreased ecological diversity across the HRB; (3) The ecological instream flow is highly sensitive to The Pacific Decadal Oscillation (PDO), North Atlantic Oscillation (NAO) and Niño 3.4 Sea Surface Temperature Index (Nino3.4). Meanwhile, the ecological instream flow along the mainstream of the HRB is highly sensitive to climate indices. While the ecological instream flow by GAMLSS model has better fitting performance in describing the extreme values and local trends.

Modeling alterations in flow regimes under changing climate in a Mediterranean watershed: An analysis of ecologically-relevant hydrological indicators

The potential response of flow regimes to future climate has crucial importance for a variety of practical applications, such as sustainable water management and ecological asset preservation. For this study, multi-site investigations of alterations in flow regimes under projected climate change were performed for one of the largest watersheds in Morocco, the Bouregreg Watershed (BW). Future daily streamflow was simulated using the eco-hydrological model Soil and Water Assessment Tool (SWAT) forced by climatic data from CMIP5 model outputs. Simulations were carried out for two periods: 2035–2050 (2040s), and 2085–2100 (2090s) under two emissions scenarios: RCP4.5 and RCP8.5. Future streamflow regimes were examined in accordance with an Indicators of Hydrologic Alteration (IHA) analysis, while being confronted with baseline flow data. Mean temperature has been predicted to increase by up to 2.79 °C in the 2090s (RCP8.5), and a higher variability in rainfall regime is expected. The results indicate that, under future changes in climate patterns, flow regimes in BW will be altered. However, the extent of alteration will be reflected unevenly among the four streams of the study watershed. The IHA analysis revealed that most of the river network will experience both a decrease in monthly flow magnitude (mostly in November and December), and an increase (dominantly in February and March) when compared to baseline. The frequency of flash pulses, and the number of zero-flow days are also expected to increase. Most of the projected alterations were estimated to become very significant in the 2090s under the RCP8.5 scenario. The potential ecological implications were also analysed, and the most sensitive streams of BW were identified to guide local water planning and ecological preservation strategies.

Impacts of streamflow alteration on benthic macroinvertebrates by mini-hydro diversion in Sri Lanka

Our study focused on quantifying the alterations of streamflow at a weir site due to the construction of a mini-hydropower plant in the Gurugoda Oya (Sri Lanka), and evaluating the spatial responses of benthic macroinvertebrates to altered flow regime. The HEC–HMS 3.5 model was applied to the Gurugoda Oya sub-catchment to generate streamflows for the time period 1991–2013. Pre-weir flows were compared to post-weir flows with 32 Indicators of Hydrologic Alteration using the range of variability approach (RVA). Concurrently, six study sites were established upstream and downstream of the weir, and benthic macroinvertebrates were sampled monthly from May to November 2013 (during the wet season). The key water physico-chemical parameters were also determined. RVA analysis showed that environmental flow was not maintained below the weir. The mean rate of non-attainment was ~ 45% suggesting a moderate level of hydrologic alteration. Benthic macroinvertebrate communities significantly differed between the study sites located above and below the weir, with a richness reduction due to water diversion. The spatial distribution of zoobenthic fauna was governed by water depth, dissolved oxygen content and volume flow rate. Our work provides first evidence on the effects of small hydropower on river ecosystem in a largely understudied region. Studies like this are important to setting-up adequate e-flows.

Environmental demand effects on the energy generation of Karkheh reservoir: Base and climate change conditions

Reservoir is a hydraulic structure that regulates river water to supply different sectors’ demands such as municipal, agricultural, and hydropower generation. Sometimes, special attention to meet aforementioned demands causes neglect of the demand and utilities of the river itself as the first main stakeholder. Thus, determination of the environmental demand is one of the effective methods that can provide appropriate potential to achieve river utilities. In this study, two hydrology-based methods, the Tennant method and the range of variability approach (RVA), are used for assessing the environmental demand to maintain the indicators of hydrologic alteration (IHA) within their ranges of natural variations. The Karkheh reservoir was selected for supplying water for downstream demands and hydropower energy generation while considering the environmental demand under the base and climate change conditions. Results showed that the inflow of the Karkheh reservoir increased under the climate change condition, the annual average hydropower energy generated increased, and the average reliabilities of municipal, environmental, and agricultural water supplies determined by the Tennant method for RCPs 2.6, 4.5, and 8.5 increased 2, 12, and 21 percent, respectively, compared to those under the base condition. Thus, there is a good potential to allocate more water to the river as a stakeholder. In addition, the RVA with adaptation to the aquatic ecosystem under the climate change condition was used to determine the environmental demand time series for representative concentration pathways (RCPs). The results demonstrated that although the RVA effectively balanced water usage for the river, the generated hydropower energy for RCPs 2.6, 4.5, and 8.5 decreased 39, 48, and 40 percent, respectively, compare to the correspondence values by the Tennant method. According to the obtained results, the Karkheh reservoir can be operated with consideration of different stakeholders such as environmental organization, hydropower energy consumers, farmers, and drinking water consumers, even under climate change conditions which need more adaptation techniques.

РЕАКЦІЯ БАГАТОРУКАВНИХ РІЧКОВИХ СИСТЕМ НА ФУНКЦІОНУВАННЯ ГІДРОЕЛЕКТРОСТАНЦІЙ

The operation of the hydroelectric power plant is one of the main reasons for the transformation of river runoff. The change in the hydrological regime affects several other processes taking place in the river channel, including the transformation of its geomorphological features. The article presents the impact of the Kaniv and Włocławek dams on the hydrological regime of the middle Dnieper River and the lower Vistula River. The nature and magnitude of changes in the Dnieper and The Vistula rivers flow regime caused by the functioning of the dams were determined using IHA (Indicators of Hydrologic Alteration) and the RVA (The Range of Variability Approach) method. It was demonstrated that the operation of the hydroelectric power plant especially in the hydropeaking system is the cause of a large flow alteration in respect of the frequency and duration of low- and high-flow pulses and the rate and frequency of change in the flow. It was assessed how the change in flow conditions in connection with the deficit of sediments affected the transformation of the Vistula and Dnieper river channels downstream of the dams. Based on our results, the reaction of the fluvial system to changes in the flow regime caused by the operation of the Kaniv and Włocławek hydroelectric power plants consisted in: 1) changing the width and depth of channels; 2) changing the size of the forms separating channels; 3) fixation of the anastomosing fluvial system. More dynamic water flows due to the operation of hydroelectric power plants modify and dynamize the natural process of evolution of a fluvial system into an anastomosing system by causing the incision and narrowing of the main channels, because of which the side channels occupy a higher position above them. On the other hand, the equalization of the water flow in the channels causes a decrease in the water level and the disappearance of the flow in the side channels. As a result, the islands separated by these channels merge and inter-channel areas are formed.

Dam-Induced Hydrologic Alterations in the Rivers Feeding the Pantanal

Tropical river basins have experienced dramatically increased hydropower development over the last 20 years. These alterations have the potential to cause changes in hydrologic and ecologic systems. One heavily impacted system is the Upper Paraguay River Basin, which feeds the Pantanal wetland. The Pantanal is a Ramsar Heritage site and is one of the world's largest freshwater wetlands. Over the past 20 years, the number of hydropower facilities in the Upper Paraguay River Basin has more than doubled. This paper uses the Indicators of Hydrologic Alteration (IHA) method to assess the impact of 24 of these dams on the hydrologic regime over 20 years (10 years before and 10 years after dam installation) and proposes a method to disentangle the effects of dams from other drivers of hydrologic change using undammed “control” rivers. While most of these dams are small, run-of-the-river systems, each dam significantly altered at least one of the 33 hydrologic indicators assessed. Across all studied dams, 88 of the 256 calculated indicators changed significantly, causing changes of 5–40%, compared to undammed reaches. These changes were most common in indicators that quantify the frequency and duration of high and low pulses, along with those for the rate and frequency of hydrologic changes. Importantly, the flow regime in several undammed reaches also showed significant alterations, likely due to climate and land-use changes, supporting the need for measurements in representative control systems when attributing causes to observed change. Basin-wide hydrologic changes (in both dammed and undammed rivers) have the potential to fundamentally alter the hydrology, sediment patterns, and ecosystem of the Pantanal wetland. The proposed refinement of the IHA methods reveals crucial differences between dam-induced alteration and those assigned to other drivers of change; these need to be better understood for more efficient management of current hydropower plants or the implementation of future dams.

A biodiversity evaluation framework for restoration of aquatic macrophyte communities in shallow lakes driven by hydrological process management

AbstractMacrophyte community diversity and composition respond to ecosystem conservation and local environmental factors. In this study, we developed a multidimensional diversity framework for macrophyte communities, including the taxonomic and functional alpha and beta diversity. We used the framework to explore the relationships among water level regimes and these diversity parameters in a case study of China's Baiyangdian Lake. Analysis of indicators of hydrologic alteration divided the water level from 1959 to 2019 into four regimes (dry, <6.42 m; low, 6.42–7.23 m; medium, 7.23–8.19 m; high, >8.19 m). Alpha and beta diversity were significantly higher in the medium regime than in the low and high regimes. Redundancy analysis indicated that the maximum water depth significantly affected taxonomic alpha diversity, and total nitrogen (TN) and chemical oxygen demand (COD) concentration significantly affected functional alpha diversity, respectively. Mantel tests showed that TN, Secchi depth (SD), and water depth in the high water level regime significantly increased the total beta diversity and turnover components. TN was the main factor that increased total taxonomic beta diversity. Water level regime mainly influenced interspecific relationships by changing the TN and COD concentration. The water level should be maintained between the medium and high water level regimes to promote restoration of the macrophyte community and improve ecosystem stability. The biodiversity evaluation framework would provide a deeper insight into the hydrological process management for restoration of aquatic macrophyte communities in shallow lakes.

Anthropogenic and Climate Effects on a Free Dam Tropical River: Measuring the Contributions on Flow Regime

The demand for freshwater resources and climate change pose a simultaneous threat to rivers. Those impacts are often analyzed separately, and some human impacts are widely evaluated in river dynamics—especially in downstream areas rather than the consequences of land cover changes in headwater reaches. The distinction between anthropogenic and climate on the components of the flow regime is proposed here for an upstream free dam reach whose watershed is responsible for the water supply in Rio de Janeiro. Indicators of hydrologic alteration (IHA) and the range of variability approach (RVA) combined with statistical analyses of anthropogenic and climate parameters indicated that (1) four river flow components (magnitude, frequency, duration, and rate of change) were greatly altered from the previous period (1947 to 1967) and the actual (1994 to 2014); (2) shifts in the sea surface temperature of the Atlantic correlated with flow magnitude; (3) the cattle activity effects on the flow regime of the studied area decreased 42.6% of superficial discharge; global climate change led to a 10.8% reduction in the same river component. This research indicated that climate change will impact the intensification of human actions on rivers in the southeast Brazilian headwaters.

Modeling Long-Term Water Allocation and Analysis of Alternative Strategic Scenarios in the Catchment Area of Bilate River, Rift Valley Lakes Basin, Ethiopia

A water shortage stress might have resulted from the extensive water resources development plan in the Bilate catchment owing to the rapidly growing population, irrigation development expansion, climatic variability, and socioeconomic development. Furthermore, the lack of sufficient knowledge about available water resources and lack of coordination in water resources management skills in the basin often aggravates the competition of fixed waterresources among the users. Therefore, modeling long-term water allocation should be implemented to determine the optimal allocation of water resources, maximize the overall benefits without compromising ecological requirements, and propose mitigation measures that may alleviate the problem of water scarcity during peak demand periods. The Water Evaluation and Planning (WEAP) model is generally used in the formulation and evaluation of alternative plansfor responding to water-related problems and water resources developments. To assist in the assessment of spatialtemporal streamflow simulations within watersheds, the Soil and Water Assessment Tool (SWAT) employed in the Bilate River and its sub-catchments. The Indicators of Hydrologic Alteration (IHA) and CROPWAT 8.0 software programs were used to estimate streamflow requirement (IFR) and the crop water requirement, respectively. Three development scenarios include the agricultural and socio-economic development effect, climatic change, and alternatives that were built in the long-term planning horizons (2013-2050). The modeling water allocation for each sub-catchment was done by considering the Ethiopian water allocation and apportionment criteria and water act priority order. The result revealed that agriculture growth (increasing irrigation projects) and socio-economic development caused a significant increase in water demand. Hence unmet water demands in different parts of the catchments were increased. Similarly, the effect of climatic variation scenarios has been increased unmet demands in the middle year of the planning horizon(2030-2050). Therefore, developing adaptation strategies scenarios helps to mitigate water scarcity and improve water availability for productive use.

Alterations in the Water-Level Regime of Tonle Sap Lake

The Tonle Sap Lake (TSL), located in southwestern Mekong Basin, is the largest freshwater lake in Southeast Asia. The water-level regime of the TSL has been changing over the last few decades due to the rapid development of water infrastructures and climate change in the Mekong Basin. This paper makes efforts to quantify the water-level regime alterations of the TSL by analyzing the pre- and post-1991 historical data of daily water levels from Kompong Luong Station. The method of modified indicators of hydrologic alteration was utilized, and the TSL’s hydrological behavior was explored further by focusing on the redistribution of hydrology and unfavorable disturbances. The results reveal that the coefficients of variation of most indicators in recent years increase compared with the preimpact years from 1960 to 1990. This demonstrates that the Mekong Basin and TSL are experiencing an increasingly unstable and varied hydrological cycle, which is more susceptible to interference with increased frequency and degree. Moreover, the system may have suffered more unfavorable human interference in dry years and in the dry season. It is expected that the findings in this paper will contribute to the protective development and adaptive management of the Mekong Basin and the TSL in the future.

Quantifying the impacts of climate change and land use on hydrological processes: A comparison between mountain and lowland agricultural watersheds

AbstractMountain and lowland watersheds are two distinct geographical units with considerably different hydrological processes. Understanding their hydrological processes in the context of future climate change and land use scenarios is important for water resource management. This study investigated hydrological processes and their driving factors and eco‐hydrological impacts for these two geographical units in the Xitiaoxi watershed, East China, and quantified their differences through hydrological modelling. Hydrological processes in 24 mountain watersheds and 143 lowland watersheds were simulated based on a raster‐based Xin'anjiang model and a Nitrogen Dynamic Polder (NDP) model, respectively. These two models were calibrated and validated with an acceptable performance (Nash‐Sutcliffe efficiency coefficients of 0.81 and 0.50, respectively) for simulating discharge for mountain watersheds and water level for lowland watersheds. Then, an Indicators of Hydrological Alteration (IHA) model was used to help quantify the alterations to the hydrological process and their resulting eco‐hydrological impacts. Based on the validated models, scenario analysis was conducted to evaluate the impacts of climate and land use changes on the hydrological processes. The simulation results revealed that (a) climate change would cause a larger increase in annual runoff than that under land use scenario in the mountain watersheds, with variations of 19.9 and 10.5% for the 2050s, respectively. (b) Land use change was more responsible for the streamflow increment than climate change in the lowland watersheds, causing an annual runoff to increase by 27.4 and 16.2% for the 2050s, respectively. (c) Land use can enhance the response of streamflow to the climatic variation. (d) The above‐mentioned hydrological variations were notable in flood and dry season in the mountain watersheds, and they were significant in rice season in the lowland watersheds. (e) Their resulting degradation of ecological diversity was more susceptible to future climate change in the two watersheds. This study demonstrated that mountain and lowland watersheds showed distinct differences in hydrological processes and their responses to climate and land use changes.

Multiple drivers of hydrological alteration in the transboundary Srepok River Basin of the Lower Mekong Region

Human-induced changes in land and water resources adversely affect global hydrological regimes. Hydrological alteration of the natural flow regime is considered to have a significant damaging and widespread impact on river ecosystems and livelihoods. Therefore, understanding the hydrological alteration of rivers and the potential driving factors affecting such alterations are crucial to effective water resources management. This study analyses the impact of changes in land use, climate, and hydropower development on the hydrological regime of the Srepok River Basin in the Lower Mekong Region. The Lower Mekong Basin (LMB) in Southeast Asia is known for its agriculture, forests, fisheries, wildlife, and diverse natural ecosystems. Historical land use and climate change are quantified (utilising European Space Agency land cover and observed meteorological data) and correlated with the hydrological indicators using the Indicators of Hydrologic Alteration (IHA) software. Moreover, pre and post impacts on the hydrological regime by hydropower development are quantified using the Range of Variability Approach (RAV) in IHA software. The results reveal that land use, rainfall, and temperature affect different aspects of the hydrological regime, with corroborating evidence to support variation among the most correlated IHA and environmental flow component (EFC) parameters with the three drivers. The highest and lowest correlations among the IHA and EFC parameters under each driver are against land use (0.85, −0.83), rainfall (0.78, −0.54), and minimum and max temperatures (0.42, −0.47). Among the parameters, the fall rate has the most significant effect on hydrological alteration of all drivers. Hydropower development in the basin mostly affects the fall rate and reversal. Identifying the connection between these multiple drivers and hydrological alteration could help decision-makers to design more efficient and sustainable water management policies.

Environmental Flows Assessment in Nepal: The Case of Kaligandaki River

Environmental flow assessments (e-flows) are relatively new practices, especially in developing countries such as Nepal. This study presents a comprehensive analysis of the influence of hydrologically based e-flow methods in the natural flow regime. The study used different hydrological-based methods, namely, the Global Environmental Flow Calculator, the Tennant method, the flow duration curve method, the dynamic method, the mean annual flow method, and the annual distribution method to allocate e-flows in the Kaligandaki River. The most common practice for setting e-flows consists of allocating a specific percentage of mean annual flow or portion of flow derived from specific percentiles of the flow duration curve. However, e-flow releases should mimic the river’s intra-annual variability to meet the specific ecological function at different river trophic levels and in different periods over a year covering biotas life stages. The suitability of the methods was analyzed using the Indicators of Hydrological Alterations and e-flows components. The annual distribution method and the 30%Q-D (30% of daily discharge) methods showed a low alteration at the five global indexes for each group of Indicators of Hydrological Alterations and e-flows components, which allowed us to conclude that these methods are superior to the other methods. Hence, the study results concluded that 30%Q-D and annual distribution methods are more suitable for the e-flows implementation to meet the riverine ecosystem’s annual dynamic demand to maintain the river’s health. This case study can be used as a guideline to allocate e-flows in the Kaligandaki River, particularly for small hydropower plants.

Development of a revised method for indicators of hydrologic alteration for analyzing the cumulative impacts of cascading reservoirs on flow regime

Abstract. The impacts of reservoirs, especially multiple reservoirs, on the flow regimes and ecosystems of rivers have received increasing attention. The most widely used metrics to quantify the characteristics of flow regime alterations are the indicators of hydrologic alteration (IHAs) which include 33 parameters. Due to the difference in the degree of alteration and the intercorrelation among IHA parameters, the conventional method of evaluating IHA parameters that assigns the same weight to each indicator is obviously inadequate. A revised IHA method is proposed by utilizing the projection pursuit (PP) and real-coded accelerated genetic algorithm (RAGA). Data reliability is analyzed by using the length of record (LOR) method. The projection values reflecting the comprehensive characteristics of the evaluation parameters are calculated. Based on these methods, a scientific and reliable evaluation of the cumulative impacts of cascading reservoirs on the flow regime was made by examining the Jinsha River. The results showed that with the increase in the number of reservoirs, the alteration degrees of IHA parameters gradually increased in groups 1, 2, 3 and 4 but decreased in group 5 (each group addresses the magnitude, timing, frequency, duration and rate of change in turn), and the flow duration curves showed a declining trend at the high-flow part and an increasing trend at the low-flow part. The flow regime alteration of the outlet section was more stable than before. This change had a negative impact on downstream fish reproduction and ecological protection. An attempt at ecological regulation was made to simulate the natural rising process of water, and four major Chinese carps have a positive response to the flood peak process caused by manual regulation.

Hydrologic impacts of cascade dams in a small headwater watershed under climate variability

Cascade damming poses a threat to watershed health; however, little is known about the hydrologic impacts of cascade dams in the context of simultaneous disturbance from climate variability. A comparison modeling approach that integrates Soil and Water Assessment Tool (SWAT) and Indicators of Hydrologic Alteration (IHA) was proposed in this study to evaluate the hydrologic impacts of cascade dams under climate variability in a small headwater watershed in Southeast China. The results showed that the verified SWAT with the reservoir module had higher Nash-Sutcliffe Efficiency values than those derived without the reservoir module. Cascade dams significantly regulated water in small flood events and reduced streamflow by enhancing evapotranspiration. Climate variability influenced the dam operation on streamflow regime. It was found that dams might cushion the pulses in wet years or fragment the pulses in dry years. Dams amplified the effects of climate variability, represented by increasing baseflow index in wet years. This research demonstrated that the comparison modeling approach proposed could provide useful insights into the hydrologic impacts of cascade dams under climate variability.

The Impact of Multi-Projects on the Alteration of the Flow Regime in the Middle and Lower Course of the Hanjiang River, China

A large number of water resources development projects have significantly changed the natural flow regime of the middle and lower reaches of the Hanjiang River, especially the Danjiangkou Reservoir, cascade reservoirs, the South-to-North Water Diversion Middle Line Project and their compensation projects, completed in 1973, 2000, and 2014, respectively. The daily streamflow data of three stations in the middle and lower mainstream of the Hanjiang River are divided into four periods corresponding to pre-impact (1954–1973), interim (1974–1999), transition (2000–2013) and post-impact (2014–2018). Eco-flow metrics and indicators of hydrologic alteration (IHA) were used to study the change of natural flow regime. The annual streamflow decreased gradually during the four periods. The construction of the Danjiangkou Reservoir increased streamflow, minimum flow value, and the number of reversals in the dry season along the middle and lower course of the Hanjiang River. Moreover, the dam reduced streamflow, maximum flow value, low pulse duration, and the rise and fall rates in the wet season. Additionally, the streamflow reduced corresponding to the completion of cascade reservoirs and the Middle Route of South-to-North Water Diversion Project. In particular, the streamflow decreased drastically from July to September, affected by the Middle Route of the South-to-North Water Diversion Project. Furthermore, the compensation projects, such as the Yangtze-Hanjiang Water Diversion Project, mitigate the reduction of streamflow from July to September in the downstream. The study provides insights into the ecological and economic benefits associated with water resources development and use in the mainstream of the middle and lower course of the Hanjiang River for the achievement of sustainable development in the region.

Which Aspects of Hydrological Regime in Mid-Latitude Montane Basins Are Affected by Climate Change?

This study analyzed the long-term alterations in runoff regime, seasonality and variability in headwater montane basins in Central Europe in response to the manifestations of climate change. We tested the common hypotheses on climate change effects on surface runoff dynamics in the Central Europe region, assuming that (i) recent climate warming will result in shifts in the seasonality of runoff, (ii) the runoff balance will remain without significant changes and (iii) that higher variability in runoff can be expected. The analyses were done on eight montane catchments in four mid-latitude mountain ranges in Central Europe, based on the uninterrupted time series of daily discharge observations from 1952 to 2018. We used 33 indicators of hydrologic alteration (IHA), 34 indicators of environmental flow components, the baseflow index, the calculation of surplus and deficit volumes and the frequency of peak and low flows. Homogeneity testing using Buishand, Pettitt and SNHT tests was applied to test the response of the hydrological alteration indicators to climate warming. We have proved the significant shifts in runoff seasonality, coinciding with the timing of the air temperature rise, marked by earlier snowmelt, followed by a decline in spring flows and a prolonged period of low flows. There was detected a rise in the baseflow index across the mountain ranges. Unlike the common hypotheses, the expected rise of runoff variability and frequency of peak flows was not demonstrated. However, we have identified a significant change of the flood hydrographs, tending to steeper shape with shorter recessing limbs as a sign of rising inner dynamics of flood events in montane catchments.

Development of a comprehensive framework for assessing the impacts of climate change and dam construction on flow regimes

The undeniable fact of climate change and dam construction alters the hydrological systems and threatens aquatic ecosystems of rivers around the world. Quantifying the impact of climate change and dam construction on flow regime is essential for water resources management and environmental protection. However, previous studies have rarely separated the effects of two factors on flow regimes, and the individual impact of each remains insufficient to date. Moreover, the existing methods have not fully captured the characteristics and temporal changes of flow regimes. In this study, we propose a new framework that integrates a streamflow reconstruction technique, indicators of hydrologic alteration (IHA), indicators of intra-annual flow variations, a revised range of variability approach to assessing the climate change and dam-induced impacts on the flow regime. The Upper Yellow River Basin (UYRB) was selected as the study area. The results show that climate change significantly reduces the monthly flow, extreme water conditions and the intra-annual indicators, and advances the Julian date of annual maximum flow. Dam construction delays the Julian date of annual maximum flow that opposes climate change impact, reduces the monthly flow in the flood season and the annual maximum flow, but increases the monthly flow in the dry season and annual minimum flow. Changes in flow regimes in the UYRB are found to be mainly due to climate change albeit there exists a cascade of dams. Based on the range of variability approach (RVA), fifteen of forty indicators are moderately changed. While the number increases to thirty-seven when considering the temporal order alteration of flow regime. The case study demonstrates that the developed framework can serve as a useful tool to evaluate the impact of climate change and dam construction on flow regimes.

Evaluation of river hydrological regime changes under the influence of Gangkouwan Reservoir

The construction of the reservoir has met human needs to a certain extent, but it has caused serious threats to river ecosystems, especially for the hydrological regime. In order to deepen the understanding of the impact of the reservoir, this paper introduces the Indicators of Hydrologic Alteration (IHA) method, constructs an indicator system that describes the changes in hydrological regime, and uses the Range of Variability Approach (RVA) to quantitatively evaluate the changes of 5 groups of 33 indexes after the construction of Gangkouwan Reservoir, thus realizing the quantitative change of the river hydrological regime. The results show that the Gangkouwan Reservoir affects the frequency and duration of high and low pulses highly, as well as in rate and frequency of water condition changes, and the integral change degree of hydrological regime is moderate.

Gradients of flow regulation shape community structures of stream fishes and insects within a catchment subject to typhoon events

Alterations in natural flow regimes caused by dams can significantly alter the aquatic habitats of stream organisms. However, few studies have characterized flow regulation to assess its impacts on stream fauna in the context of interannually variable extreme floods. This study aims to understand the variation in stream animals along flow regulation gradients due to hydropower dams in a catchment experiencing typhoons. We observed freshwater fishes and stream insects at fully regulated sites (receiving residual flow), moderately regulated sites (receiving hydropower outflow), and nonregulated site (tributary) in the Mimi River catchment in southern Japan, in summer and winter from 2010 to 2018. We computed indicators of hydrologic alteration (IHA) in each calendar/water (July to June) year from 2007 to 2017 and selected subsets of IHA based on principal component analysis (PCA) and variance inflation factor. The largest variance was mainly explained by minimum discharge levels (e.g., 30-day annual minimum) and flow variability among IHAs, distinguishing the moderately regulated and nonregulated sites from fully regulated sites because of residual flow and suppressed high pulses in the fully regulated sites. Generalized additive models revealed that annual maxima of specific discharge were most significant predictors of fish and insect metrics while its effects were generally inconsistent between summer and winter. Non-metric multidimensional scaling revealed that insect communities were clustered into the regulation extents in both seasons. The differences in winter fauna between the regulated and nonregulated sites, characterized by Ephemeroptera-Plecoptera-Trichoptera abundance, were associated with maximum discharge and high pulse numbers. Fish community variation did not correspond to flow regime gradients. Our findings on mechanistic ecohydrological consequences of various flow regulations, supported by long-term observations, will be useful for river managers attempting to compensate for alterations in flow regime and ecological integrity.