Altered Flow Regimes Research Articles

Evaluation of Gangetic dolphin habitat suitability under hydroclimatic changes using a coupled hydrological-hydrodynamic approach

The aquatic ecosystems are an integral part of the global environment and play a critical role in hydrogeological processes in the rivers. In recent decades, the external stressors on the aquatic species have significantly increased due to hydrologic alterations, human activities, and anthropogenic changes to their natural habitat. Global climate change has led to rivers' hydrological flow regime shifts, leading to unsuitable habitat conditions. It is, therefore, crucial to assess the potential implications of climate change on habitat suitability to ensure the long-term sustainability of freshwater species. In this direction, we investigated the association between endangered Gangetic dolphin populations and climate-driven hydrologic flow regime alterations in the Kulsi river, India. We developed a coupled eco-hydraulic framework comprising hydrological and hydrodynamic modeling to study the impact of past and projected climate change scenarios on the habitat suitability of target species. The framework was tested on a 15-km stretch of the Kulsi River, where the dolphin population has significantly declined in recent years. The temporal changes in the Weighted Usable Area (WUA) were analyzed using flow parameters and habitat suitability curves. Our findings suggest that the dolphin population decline coincided with a decrease in WUA, indicating a strong association between flow regimes and habitat suitability. Under climate change scenarios, multi-model climate projections and hydrological-hydrodynamic simulations show a rising trend in precipitation and streamflow in the basin, with substantial uncertainty. Higher flow depth and velocity would enhance WUA (habitat suitability). Still, the proposed river development projects in upstream regions could pose a serious threat to fragile dolphin communities by changing the seasonal flow patterns. The findings of this study can be included in conservation action plans and flow regulations strategies in upstream projects to ensure the long-term survival of endangered species.

Range-wide persistence of the endangered arroyo toad (Anaxyrus californicus) for 20+ years following a prolonged drought.

Prolonged drought due to climate change has negatively impacted amphibians in southern California, U.S.A. Due to the severity and length of the current drought, agencies and researchers had growing concern for the persistence of the arroyo toad (Anaxyrus californicus), an endangered endemic amphibian in this region. Range‐wide surveys for this species had not been conducted for at least 20 years. In 2017–2020, we conducted collaborative surveys for arroyo toads at historical locations. We surveyed 88 of the 115 total sites having historical records and confirmed that the arroyo toad is currently extant in at least 61 of 88 sites and 20 of 25 historically occupied watersheds. We did not detect toads at almost a third of the surveyed sites but did detect toads at 18 of 19 specific sites delineated in the 1999 Recovery Plan to meet one of four downlisting criteria. Arroyo toads are estimated to live 7–8 years, making populations susceptible to prolonged drought. Drought is estimated to increase in frequency and duration with climate change. Mitigation strategies for drought impacts, invasive aquatic species, altered flow regimes, and other anthropogenic effects could be the most beneficial strategies for toad conservation and may also provide simultaneous benefits to several other native species that share the same habitat.

Assessment of impacts of altered environmental flow on fishing in lower Damodar river basin, India

Rivers are one of the prime sources of freshwater and act as the arteries of the Earth. While the growing pressure of meeting freshwater demands through extensive large and small-scale water infrastructures is indispensable, maintaining the river's natural flow is vital in sustaining the aquatic ecosystem harbored within it. Hence, it is essential to regulate the environmental flow for the sustainability of the rivers and their ecosystem management. This paper focused on analyzing the importance of maintaining the environmental flow by computing the degree of deviation in the river flow regime from the natural flow conditions. It used the Range of Variability Approach (RVA) to calculate the degree of deviation while also lending a special focus on the implications of altered river flow regime on the socio-economic activities especially fishing as a livelihood for the communities residing along the flanks of river Damodar in the downstream region. The daily discharge data measured during pre-and post-dam construction at the Durgapur barrage site of the lower Damodar river basin were used to compute the degree of alteration. It applied the convergent parallel mixed methodology to simultaneously analyse the qualitative responses and the quantitative data to effectively interpret the impact of altered environmental flow on the fishing livelihood of the communities. Thus, the analysis emphasized the importance of maintaining the environmental flow for ensuring the well-being of humans reliant on river systems. This shall also accentuate and contribute to the idea of balancing between development and sustainability.

Identifying hydrologic reference stations to understand changes in water resources across Vietnam - a data-driven approach

Among the impacts of climate change and variabilities, change in the terrestrial water cycle has been investigated extensively due to the importance of water resources to the Earth System. The detection and attribution of changes in river flows, however, are usually complicated by the impacts of on-ground human activities such as urbanization or dam construction that have altered flow regimes. As a result, hydrological reference stations – gauges measuring river flows of catchments that are unregulated - have been identified in many countries to provide streamflow records that are suitable for climate studies. Such a network, to the best of our knowledge, has not been promoted widely in Vietnam, making it difficult to determine the actual impact of climate change and variability to river flow regimes at the national scale. To address this limitation, this study uses a data-driven approach to identify stations that have not been influenced substantially by human activities for Vietnam. Specifically, we have carefully assessed streamflow records at 68 locations that are not influenced by tidal regime to identify stations with relatively good data quality. The drainage area associated with each of these stations was then delineated following international standards, and then used to identify catchments that were not associated with large dams. The catchment boundary was also used to extract land surface information, available through an ensemble of different satellite-based data products, to further identify catchments that are not featured by large urban areas, or experienced a substantial change in land cover during the 2000-2019 period. Using these criteria, this study suggested two subsets of stations distributed across the countries, providing a good starting point for future investigations into the impacts of climate change on water resources in Vietnam. The investigation also suggests that more investments are required to maintain and expand the hydrologic reference network for Vietnam.

Assessing Hydrological Alteration Caused by Climate Change and Reservoir Operations in the San Joaquin River Basin, California

Freshwater aquatic ecosystems are highly sensitive to flow regime alteration caused by anthropogenic activities, including river regulation and atmospheric warming-induced climate change. Either climate change or reservoir operations are among the main drivers of changes in the flow regime of rivers globally. Using modeled unregulated and simulated regulated streamflow under historical and future climate scenarios, this study evaluated potential changes to the flow regime due to climate change and reservoir operations for the major tributaries of the San Joaquin River Basin, California United States. We selected a set of Indicators of Hydrologic Alteration (IHA) to evaluate historical and projected future trends of streamflow dynamics: rise and fall rates, durations and counts of low and high pulses, and the magnitude of extremes. Results show that most indicators have pronounced departures from baseline conditions under anticipated future climate conditions given existing reservoir operations. For example, the high pulse count decreases during regulated flow conditions compared to increased frequency under unregulated flow conditions. Finally, we observed a higher degree of flow regime alteration due to reservoir operations than climate change. The degree of alteration ranges from 1.0 to 9.0% across the basin among all future climate scenarios, while reservoir operations alter the flow regime with a degree of alteration from 8.0 to 25%. This study extends multi-dimensional hydrologic alteration analysis to inform climate adaptation strategies in managed river systems.

Distribution and diversity of benthic macroinvertebrates in the Mohlapitsi River, South Africa

Freshwater ecosystems are facing degradation from human activities in the form of alterations of flow regimes, changes in land-use, and intensive water abstraction, in turn generating adverse effects on biodiversity and ecological functionality. Efficient assessment of river/stream ecosystem response to such anthropogenic changes is urgently needed. Many human activities that have an effect on water quality and river health are increasing along the Mohlapitsi River, which used to be one of the rivers with good water quality in South Africa. The aim of the study was to assess spatial variation in macroinvertebrate assemblages in relation to water quality of the Mohlapitsi River. A combination of canonical correspondence analysis and univariate analyses were used to examine the macroinvertebrate assemblages at six different sites of the Mohlapitsi River. The spatial difference in macroinvertebrate abundance was mostly related to changes in water quality. The number of taxa and the diversity of macroinvertebrates remained relatively high across the river as compared to other rivers in the Olifants River System. The midstream and downstream sites were mostly dominated by macroinvertebrates tolerant to disturbance/pollution. The most abundant family was the Thiaridae (about 60%) and mainly occurred in the midstream and downstream sites of the river (more disturbed sites). The study showed a higher evenness index in the upstream than the midstream and downstream sites which is an indication of good water quality at the upstream sites of the river. The results suggest that the river is being subjected to a moderate environmental pollution, which requires continuous assessment and monitoring to determine causes and initiate remedial measures.

Biological assessment of western USA sandy bottom rivers based on modeling historical and current fish and macroinvertebrate data.

Biological monitoring is important for assessing the ecological condition of surface waters. However, there are challenges in determining what constitutes reference conditions, what assemblages should be used as indicators, and how assemblage data should be converted into quantitative indicator scores. In this study, we developed and applied biological condition gradient (BCG) modeling to fish and macroinvertebrate data previously collected from large, sandy bottom southwestern USA rivers. Such rivers are particularly vulnerable to altered flow regimes resulting from dams, water withdrawals and climate change. We found that sensitive ubiquitous taxa for both fish and macroinvertebrates had been replaced by more tolerant taxa, but that the condition assessment ratings based on fish and macroinvertebrate assemblages differed. We conclude that the BCG models based on both macroinvertebrate and fish assemblage condition were useful for classifying the condition of southwestern USA sandy bottom rivers. However, our fish BCG model was slightly more sensitive than the macroinvertebrate model to anthropogenic disturbance, presumably because we had historical fish data, and because fish may be more sensitive to dams and altered flow regimes than are macroinvertebrates.

Basal resources of river food webs largely affect the fatty acid composition of freshwater fish

1.Overfishing, altered flow regimes, loss of connectivity, pollution and other direct human disturbances have had a significant impact on freshwater fish biodiversity. While direct effects of these disturbances are well documented, some can also lead to changes in the nutritional composition at the base of freshwater food webs and may affect fish growth and reproduction. Thus far, little is known about how changes in the nutritional composition at the base of freshwater food webs are reflected in fish production and fatty acid composition.2.We conducted a field study in subalpine rivers in Austria to examine how variations in the food quality of basal food sources affect the biochemical composition of freshwater fish. Basal food sources (terrestrial leaves and periphyton), the abundant fish taxa brown trout (Salmo trutta) and European bullhead (Cottus gobio) and their macroinvertebrate prey were collected and their stable carbon isotopes (δ13C) and fatty acid (FA) compositions were measured.3.Our results show that periphyton was the major source of dietary carbon for fish and most invertebrates, except shredders, and a high-quality food for all consumers that provides long-chain polyunsaturated FA (LC-PUFA). In contrast, submerged leaves contained very low content of LC-PUFA and were low-quality food for consumers.4.Changes in periphyton FA across these river ecosystems were tracked in macroinvertebrate FA profiles and in the FA composition of muscle tissues in both fish species. In contrast, the FA composition of fish brain remained unaltered across the study streams.5.The docosahexaenoic acid (DHA, 22:6ω3) content in muscle tissues of S. trutta remained stable and did not correspond to changes of periphyton FA, indicating strong regulation of DHA in this species which is independent of aquatic food sources. In contrast, muscle DHA and eicosapentaenoic acid (EPA, 20:5ω3) content of C. gobio significantly declined when periphyton quality decreased, reflecting the strong impact of the nutritional quality of periphyton on the FA composition of this bottom-dwelling fish.6.Reduced nutritional quality of periphyton led to reduced LC-PUFA in muscle tissues of bottom-dwelling bullhead and even piscivorous brown trout, suggesting that changes of FA composition at the base of river food webs cannot be compensated by intermediate consumers, such as benthic invertebrates, that also convey dietary FA to fishes. This study highlights how subtle human disturbance to streams can affect freshwater fish species through changes to the nutritional quality of their basal food sources.

Relationship between Thermal Variance and Hatchery Estimates of Fertility in a Multispecies Assemblage of Anadromous Salmonids in Response to Managed Flows

Our study sought to identify a regional explanation for declining fertility in stocks of co-occurring salmonids in the upper Trinity River, northern California, USA. We focused on evaluating the relationship between thermal variance in river water and hatchery-measured estimates of female fertility as a function of highly managed annual flow regimes. We evaluated annual and seasonal variation in volume of flow and water temperature in response to managed flows associated with annual in-river restoration actions. We assessed the relationship between flow-mediated thermal variance in river water and estimates of fertility in hatchery parental bloodstock in a multi-species assemblage of co-occurring anadromous salmonids. Results of our study found: 1) significant differences between flow-types in flow volume and the thermal variance evaluated with reference to the historical run-time schedule of each taxon; 2) significant differences among species-specific flow-types for each environmental variable measured; 3) significant declines in the averaged daily number of total eggs harvested in all species except steelhead; 4) significant differences in the estimates of fertility for all species-specific flow-types, in which 83.3% of planned pairwise comparisons differed between flow-types for each taxon; 5) significant declines in the annual estimates of fertility in all species; and 6) significant negative correlations between species-specific estimates of fertility and thermal variance in water temperature. Overall, our findings suggest that increased temperature variation from managed flows may reduce estimates of fertility in hatchery-spawned salmonids; and that concordant patterns in response to thermal variance in species with divergent life histories may in part be a function of anthropogenic altered flow regimes on ecosystem processes and the fisheries resources they support.

Effects of experimental multi-season drought on abundance, richness, and beta diversity patterns in perennially flowing stream insect communities

Freshwater systems are projected to experience increased hydrologic extremes under climate change. To determine how small streams may be impacted by shifts in flow regimes, we experimentally simulated flow loss over the span of three summers in nine 50 m naturally fed stream channels. The aquatic insect community of these streams was sampled before, during, and after experimental drought treatments as well as following one unforeseen flood event. Abundance, richness, and beta diversity were measured as indicators of biotic effects of altered flow regimes. Abundance declined in proportion to flow loss. In contrast, we observed a threshold response in richness where richness did not decrease except in channels where losses of surface flow occurred and disconnected pools remained. The flood reset this pattern, but communities continued their prior trajectories shortly thereafter. Beta diversity partitions suggested no strong compositional shifts, and that the effect of drought was largely experienced uniformly across taxa until flow cessation. Pools served as a refuge, maintaining stable abundance gradients and higher richness longer than riffles. Upon flow resumption, abundance and richness returned to pre-treatment levels within one year. Our results suggest that many taxa present were resistant to drought conditions until loss in surface flow occurred.

Upstream migration of anadromous and potamodromous brown trout: patterns and triggers in a 25-year overview

River fragmentation and alterations in flow and thermal regimes are the main stressors affecting migrating fish, which could be aggravated by climate change and increasing water demand. To assess these impacts and define mitigation measures, it is vital to understand fish movement patterns and the environmental variables affecting them. This study presents a long-term (1995–2019) analysis of upstream migration patterns of anadromous and potamodromous brown trout in the lower River Bidasoa (Spain). For this, captures in a monitoring station were analyzed using Survival Analysis and Random Forest techniques. Results showed that most upstream movements of potamodromous trout occurred in October–December, whereas in June–July for anadromous trout, although with differences regarding sex and size. Both, fish numbers and dates varied over time and were related to the environmental conditions, with different influence on each ecotype. The information provided from comparative studies can be used as a basis to develop adaptive management strategies to ensure freshwater species conservation. Moreover, studies in the southern distribution range can be crucial under climate warming scenarios, where species are expected to shift coldwards.

Linking flow alteration with fish assemblage structure in a river regulated by a small hydropower project in the Western Ghats of Karnataka, India

AbstractSmall hydropower projects (SHPs) are promoted as low‐impact alternatives for large hydropower. SHPs are generally commissioned on small‐ to medium‐sized mountainous rivers, often in biodiverse regions, with backing in the form of subsidies, facultative policies and exemption from impact assessments as they are considered ‘green’. However, the ecological impacts of SHPs are understudied especially in highly seasonal tropical streams of Western Ghats of India, a global biodiversity hotspot and a distinct freshwater fish eco‐region. We compared SHP‐affected segments of a dammed and an undammed river in the Western Ghats of Karnataka, to assess how altered flow regime affects seasonal variability in habitat and water quality, and influences fish assemblage structure. We found that flow alteration by the SHP varied between different segments of the dammed river and with season. Furthermore, the nature of flow alteration influenced habitat variability, water quality and fish assemblage response in the dammed river. We observed that the dewatered segment of the dammed river experienced a lotic to lentic shift in habitat and water quality, which favoured fish species with eurytopic affinities. Fluctuating flows in the downstream segment subdued natural variability in flow regime and created novel habitats and water‐quality conditions, affecting fish assemblages. The upstream segment of the dammed river retained natural variability in habitat and water quality, but did not mimic the undammed river in terms of fish composition. We also observed potential constraints on recruitment for migratory species of fish in the dammed river. Based on our results, we suggest how the placement of dewatered segment, and timing the closure of SHP operation in dry season based on ecological thresholds are potential solutions to mitigate the impacts of the SHPs. Furthermore, we recommend effective impact assessments, and adaptive management with active interventions to maintain genetic and ecological connectivity, as key to enhance the sustainability of the SHPs.

Do we prioritize floodplains for development and farming? Mapping global dependence and exposure to inundation

Global wetlands and floodplains offer benefits and perils alike for human society. For example, humans rely on natural flood cycles for fisheries and agriculture, yet flooding also caused nearly one trillion USD in damage in the past 30 years and impacts millions of people every year. Looking forward, altered flow regimes or increased drought conditions are expected to affect the natural inundation cycle and its ecosystem services. The current and potential future impacts of flooding and drying events warrant increasing efforts to quantify our dependence and exposure within flooded areas, since any change from current inundation patterns is expected to have consequences for those who rely on regular flood occurrences. This paper provides a baseline global assessment of the dependence and exposure of human populations, urban areas, roads, and agriculture on current inundation patterns. The analysis uses a spatially explicit inundation map at ∼500 m resolution (GIEMS-D15) derived from satellite remote sensing to represent flooding extents and overlays it with current population and land use maps. We find that 35% of the analyzed population, or 2.0 billion people, live inside areas that are prone to inland flooding, which comprise only 12% of the land surface area (excluding marine coastal areas), confirming that population densities within inundation zones are about three-times above global average. Likewise, 35% of urban areas potentially experience regular, seasonal, or infrequent flooding. Agriculture shows a similar pattern with 24% of the world’s cropland in areas of recurring inundation. Finally, we estimate that 18% of the global road network is exposed to inundation during high water periods. These global estimates demonstrate a preferential tendency of human populations, infrastructure, and agriculture to be co-located within inundation areas, making related anthropogenic activities highly susceptible to future changes in flood regimes. The results are intended to offer a suite of first-order estimates as partial input to more holistic risk and vulnerability assessments and to ultimately improve environmental planning and policy at large scales.

A new strategy for environmental flow management by using the remote sensing method

Implementing environmental flow (e-flow) is a key measure for restoring and managing river ecosystems. However, illegal competition for water resources or alterations of the natural flow regimes can result in the shortage of e-flow and degradation of river ecosystems. Monitoring and managing e-flow is increasingly critical and necessary in some regions. In this study, a monitoring method and guarantee rate evaluation system for e-flow was developed using remote sensing and hydrological data of the Jiulongjiang and Taizi rivers, China. The results indicated that the monthly e-flow varied with the water demand, ranging from 12.60 m3/s to 189.50 m3/s and 3.50 m3/s to 57.70 m3/s at Punan station, Jiulongjiang River and Tangmazhai station, Taizi River, respectively. Moreover, e-flow accounted for 24% of the average annual runoff for both rivers, which indicated that the ecological environment was in a fair or degrading state. Moreover, the guarantee rate of e-flow at Tangmazhai station is 100%, which indicates that the e-flow meets the requirements and is consistent with the results of the e-flow guarantee rate calculated by the actual measured flow. The guarantee rate of e-flow at Punan station is 0%, and exhibits a certain error with the actual measurement results; this is because a rectangular section exists between the maximum and minimum ecological water levels, which corresponds to a small change in the ecological water surface width of 0.9 m. The low-resolution remote sensing used in this study cannot capture this change, thus causing a large error in the measured result; however, this issue can be addressed by improving the remote sensing technique. The results showed that the monitoring method and guarantee rate evaluation of e-flow can be adopted for several basins, including larger scale river basins, and can improve e-flow management for mitigating the degradation of river ecosystems.

Effects of antecedent drying events on structure, composition and functional traits of invertebrate assemblages and leaf‐litter breakdown in a former perennial river of Central Apennines (Aterno River, Abruzzo, Central Italy)

AbstractBecause of global change and increasing anthropogenic pressures, non‐perennial rivers and streams are predicted to drastically increase in the European‐Mediterranean region. Some river basins already subject to reduced levels of available superficial flow may present a further reduction, with a significant increase in intermittence phenomena and complete drought of former perennial rivers. In this context, a sound knowledge of the ecological effects of increasing drying events on these watercourses may help to better predict impacts of the altered flow regime on structure and functions of freshwater ecosystems. In this paper, we assessed the long‐term response of invertebrate assemblages and ecosystems processes to antecedent drying events (drying memory) in a Central Apennine river (Italy). We demonstrated that compared to the perennial reach, the 7‐km downstream intermittent site, after more than 1 year from a complete superficial flow resumption, still conserved the ‘memory’ of past disturbance with marked differences in structure, composition and functional traits of assemblages which, in turn, negatively influenced the leaf‐litter breakdown process. Despite total abundance and taxa richness were on average higher at the intermittent site, antecedent droughts determined a decline of shredders and scrapers and an increase of collectors. In addition, some more sensible, semivoltine and rheophile taxa were replaced by generalist, multivoltine and more resistant taxa. Our findings confirm and extend the ‘drying memory’ hypothesis and suggest that irregular drying events in former perennial Apennine rivers may have dramatic long‐term effects on both structure and functions of lotic ecosystems.

The effect of altered flow regimes on aquatic primary producer communities: Diatoms and macrophytes

AbstractRivers are intensively managed worldwide through unprecedented flow regime alterations on a global scale. This has led to an increasing interest in the development of quantitative tools to assess the ecological response of organisms to flow alteration. To date, studies reflect a large diversity of responses that make the intensity and prevalence of effects difficult to generalize. The present study analysed how flow alterations caused by dams affect the structure, composition and traits of diatoms and macrophytes in three Spanish river basins (Cantabric, Ebro and Duero). By using a control‐impact design based mainly in hydrological similarity, our results showed consistent patterns of change in diatom and macrophyte communities. Our study showed a shift from resistant traits such as non‐colonial diatom forms and crust‐forming algae, which are adapted to the extreme events and natural dynamism of unregulated rivers, towards planktonic diatoms, free‐floating algae and the mass development of aquatic plants in hydrological altered sites. Both communities shared common thresholds of response to altered hydrological attributes that could be considered in a flow management context. The hydrological indices that impacted diatom and macrophyte communities the most were related with the magnitude and duration of minimum flows. However, our results also show that it is important to consider the interrelationships between the different hydrological attributes such as the seasonal variability of monthly flows, the magnitude of maximum annual extremes, the timing of flow events, and the frequency and rate of flow changes.

Uncertainty analysis for evaluating flow regime alteration of Jinsha River based on Indicators of Hydrologic Alteration

ABSTRACT The uncertain relationship between data length and evaluation of hydrological alteration has perplexed researchers. In this study, the length of record (LOR) method is applied to analyse the uncertainty in the impact of different data lengths on the Indicators of Hydrologic Alteration (IHA) evaluation in the Jinsha River. The results indicate: (1) For the pre-impact period, a daily streamflow data length of 20 years should be required to meet all the indicators, but 5–10 years of data could be sufficient when analysing some specific indicators. (2) A logarithmic correlation was found between the LOR results and the coefficient of variation (CV) of the IHA statistics, which can be considered reference factors to reduce the computational complexity when we expect to obtain LOR results from other nearby hydrological stations. (3) For the post-impact period, using a data length of 10 years is sufficient to evaluate the impact of large reservoirs on the river hydrological regime, and the actual alteration of hydrological regime would be overestimated by using a shorter data length.

Hydrologic flow regimes in humid tropics river basin.

The study is carried out to understand the impact of the land-use change in terms of alteration in flow regimes, which are understood to be a leading cause of ecological and environmental deterioration in riverine systems. Meenachil river in the humid tropical region of Kerala, India, is one of a kind river with human settlement along the banks for all its 78 kms of flow through the Kottayam District. The analysis of streamflow from four stream gauge stations was done using Range Variability Approach. The analysis was down as a two-time period analysis with the parametric approach with the period separation taken according to prior studies on land-use change. The analysis shows a high degree of alteration, which can be attributed to the land-use change and can be understood as the root cause for the deterioration of water quality and also the ecological distress, which is well documented in the downstream and watershed regions of the river.

Combining split-sample testing and hidden Markov modelling to assess the robustness of hydrological models

Abstract. The impacts of climate and land-use changes make the stationary assumption in hydrology obsolete. Moreover, there is still considerable uncertainty regarding the future evolution of the Earth’s climate and the extent of the alteration of flow regimes. Climate change impact assessment in the water sector typically involves a modelling chain in which a hydrological model is needed to generate hydrologic projections from climate forcings. Considering the inherent uncertainty of the future climate, it is crucial to assess the performance of the hydrologic model over a wide range of climates and their corresponding hydrologic conditions. In this paper, numerous, contrasted, climate sequences identified by a hidden Markov model (HMM) are used in a differential split-sample testing framework to assess the robustness of a hydrologic model. The differential split-sample test based on a HMM classification is implemented on the time series of monthly river discharges in the upper Senegal River basin in West Africa, a region characterized by the presence of low-frequency climate signals. A comparison with the results obtained using classical rupture tests shows that the diversity of hydrologic sequences identified using the HMM can help with assessing the robustness of the hydrologic model.

Evaluation of instream ecological flow with consideration of ecological responses to hydrological variations in the downstream Hongshui River Basin, China

Due to increasing anthropogenic activities, especially with cascade reservoirs having been constructed, the hydrological regimes of the Hongshui River (HSR) Basin which were mainly shaped by precipitation in the undisturbed period, have inevitably changed, making further impacts on riverine ecological environment. Although previous researches to analyze hydrological alterations of flow regimes are numerous, insightful investigation into ecological impacts behind them is needed for watershed management and riverine ecosystem protection. Employing two generalized eco-flow indicators (ecodeficit, ecosurplus), fluvial biodiversity Shannon Index (SI), and multiple hydrological indicators: Indicators of Hydrologic Alteration (IHA), integrated degree of hydrological variation (D0) and Dundee Hydrological Regime Alteration Method (DHRAM), this study focuses on the evaluation of temporal variations of ecological flow in multiple time scales while considering ecological responses to evolutionary characteristics of flow regimes which were chronologically subject to rainfall and reservoirs-disturbances; in addition, an effective method that combines eco-flow indicators and ecologically-relevant hydrological indicators (ERHIs) to evaluate eco-hydrological regime was proposed. The results indicate that: (1) dam-disturbance has broken the close relationships between ecological flow and precipitation in the near-natural period, causing high level of ecodeficit (0.53 the largest) in flood season and astonishing ecosurplus (1.99 the maximum) in dry season; (2) flow regimes have greatly altered and the degree of integrated hydrological variations reaches 60.22%, with an ecological hazard class at level 3, indicating the riverine ecological environment is at risk of facing moderate damage; (3) contributions of seasonal deficit or surplus of ecological flow have been greatly influenced by reservoirs operations, although with astonishing increment of total seasonal ecosurplus, SI has been abnormally decreasing after 1992 when major reservoir came to operate, indicating the degradation of fluvial biodiversity in the HSR Basin due to dam regulation; (4) the combination of eco-flow indicators and ERHIs, which is capable of mirroring the key hydrological information and related ecological connotation, is prove to be an effective method to evaluate the eco-hydrological regimes. The findings of the study could be instructive to relative researches in other cases and provide scientific guidance for local watershed management.