Instream Flow Requirements Research Articles

Evaluation of water shortage and instream flows of shared rivers in South Korea according to the dam operations in North Korea

Abstract The Korean Peninsula's mountainous terrain poses challenges to effective water resource management. Notably, two significant river basins, North Han River and Imjin River basins, are essentially shared rivers originating in North Korea. After the construction of various dams in North Korea, billions of tons per year of water annually decreased from the upper reaches of these rivers of North Korea to South Korea. This study conducted an impact analysis on two major river basins affected by dam operations in North Korea. Both before and after the Imnam Dam operation, significant reduction (27.7%) in the average monthly inflow was observed, and the total release of the Hwacheon Dam in South Korea decreased by 40.2%. The analysis of instream flow indicated that the operation of dams in North Korea had a substantial impact on fulfilling instream flow requirements for dams located in North Han River and Imjin River basins. To ensure instream flow, this study proposed two plans. The first plan involved the utilization of existing dams in the North Han River basin, while the second plan suggested connecting the dams in North Korea, taking into account the shared rivers.

Detection and Analysis of the Variation in the Minimum Ecological Instream Flow Requirement in the Chinese Northwestern Inland Arid Region by Using a New Remote Sensing Method

With the development of human society, the balance between the minimum ecological instream flow requirement (MEIFR), which is an essential part of the ecological water demand in arid areas, and anthropogenic water depletion has received increasing attention. However, due to the lack of hydrological station data and river information on arid basins, previous researchers usually considered only the individual ecological water demand of rivers, lakes, or oases. To address this issue, a new method that combines river hydraulic parameters and the wet circumference obtained by an unmanned aerial vehicle (UAV) and remote sensing hydrological station (RSHS) technologies was applied to obtain the MEIFR and, then, systematically and quantitatively explore the balance from the perspective of the entire basin of Aiding Lake from 1990 to 2022, which is the lowest point of Chinese terrestrial territory. The results showed the following: (1) since 1990, the discharge of the seven rivers in the study area increased by 1–6%, and the MEIFR of these rivers increased by 15–100%; both quantities decreased by 3–5% from the upper to the lower reaches of the basin; (2) the surface area and water level of Aiding Lake decreased by 5% and 14%, respectively, but the MEIFR first decreased by 25% from 1990 to 2013 and, then, increased by 66.7% from 2013 to 2022; and (3) from 2011 to 2022, the MEIFR and anthropogenic water depletion exhibited a balance. Against the background of climate change, this research revealed that the MEIFR of the rivers in the Aiding Lake Basin have shown an upward trend over the past 30 years and quantitatively determined the above balance relationship and the period of its occurrence. This study supplied a method that could provide guidance for water resource management by decision-makers at a global level, thus helping achieve the sustainable development goals (SDGs).

Unveiling an Environmental Drought Index and its applicability in the perspective of drought recognition amidst climate change

As a complex natural disaster, drought encompasses significant and wide-ranging impacts on various environmental aspects. While meteorological, hydrological, agricultural, and socioeconomic droughts have been extensively studied, the scientific understanding of environmental droughts (the proposed fifth classification) remains relatively limited, hampering practical assessment efforts. To address this gap, the present study, for the first time, conducted a rigorous assessment of the applicability of a novel method, namely the heuristic method, in conjunction with a newly developed Environmental Drought Index (EDI). The present study thoroughly analyzed environmental drought events in India's Brahmani River basin, specifically focusing on the Jaraikela catchment. Firstly, the Minimum in-stream Flow Requirement (MFR) was determined using Tennant’s method to synthetically estimate discharge rates to maintain the optimum flow range during the historical period (1980–2014). Secondly, Drought Duration Length (DDL) was calculated by counting consecutive water deficit months with negative monthly Streamflow Rate (SFR) and MFR differences. Three General Circulation Models (GCMs) output ensembles, namely EC-Earth3, MPI-ESM1-2-HR, and MRI-ESM2-0, participating in CMIP-6, were used for past (1980–2014) and future periods (FP-1: 2015–2022, FP-2: 2023–2045) under emission scenarios SSP245 and SSP585. The HydroClimatic Conceptual Streamflow (HCCS) model was employed to simulate the historical and future SFR. Thirdly, the largest water deficit magnitude during DDL was used to estimate the Water Shortage Level (WSL). Finally, integrating DDL and WSL provided the EDI for each environmental drought event. Results demonstrated a strong correspondence between the simulated EDI obtained using MPI-ESM1-2-HR under SSP585 and the observed EDI values, thereby indicating the credibility of the EDI in assessing environmental droughts. Furthermore, the study found severe droughts (i.e., EDI-3) dominating (71–73% of all droughts; occurring during non-monsoonal months) during FP-2 under SSP585 across all three GCMs, differing from moderate droughts in SSP245 of FP-2, both scenarios of FP-1, and the historical period. Based on the findings, the study finally proposed several adaptive measures to mitigate the impacts of increasing environmental drought events in the catchment.

Augmenting environmental flow information with water temperature: case study in Eastern Canada

The increasing global water demand and climate change put freshwater resources and riverine ecosystems at risk of increasing scarcity and conflict in water usage. Stream biota may be confronted with increasing stressful aquatic habitat conditions due in part to increasing water temperatures. In response to these issues, environmental flows play a crucial role in flow assessment, water resource management and the protection of aquatic biota. Environmental flows (eflows), also known as instream flow requirements, refer to the amount of water needed in rivers to maintain a balanced aquatic ecosystem. Recently, the inclusion of river temperature in the assessment of eflows has raised interest, especially in the context of climate change and dam operations, which are altering the river thermal regimes and affecting aquatic habitat. This study focuses on hydrological metrics that can be used to prescribe eflows in Atlantic Canada and Quebec (Eastern Canada). Eflow analyses were conducted jointly with the analyses of river temperatures at 61 sites. The results show that summer environmental flow metrics can be associated with relatively high water temperatures during a period when water withdrawals may be important. Classifying rivers according to their thermal regime during summer low flow periods prior to prescribing an eflow target is therefore recommended.

Chinook salmon rearing habitat–discharge relationships change as a result of morphodynamic processes

AbstractRelationships between fluvial aquatic habitat availability and discharge are often assumed to remain static when used with hydrologic datasets to analyze changes in habitat availability over time. Despite this assumption, studies have observed significant changes in aquatic habitat availability before and after restoration projects, dam removals, and extreme flood events. However, research is lacking on how aquatic habitat changes as a result of morphodynamic processes during more commonly occurring hydrologic conditions. This study compared Chinook salmon (Oncorhynchus tshawytscha) rearing habitat availability at 19 discharges before and after a relatively mild 8‐year hydrologic period punctuated with modest floods on the lower Yuba River in California, USA. During this time, the total area of rearing habitat remained relatively consistent at discharges <2× bankfull but decreased by up to 25% at discharges >2× bankfull. Significant decreases in rearing habitat area appeared to be the result of widespread erosion on floodplains, terraces, and lateral bars, even after only modest floods. As a result, spatially delineated areas of lost habitat tended to increase in water depth and velocity at baseflow, bankfull, and floodplain‐filling discharges, while areas of gained habitat decreased in depth and velocity. Although these specific results may not apply to all rivers around the world, the finding that habitat–discharge relationships change as a result of morphodynamic processes likely does transfer globally and should be considered when making long‐term regulatory and management decisions, such as instream flow requirements and habitat restoration plans.

Assessment of environmental flow requirements using a coupled surface water-groundwater model and a flow health tool: A case study of Son river in the Ganga basin

Rapidly increasing population, industrialisation, and unsustainable consumption have resulted in deterioration of water quantity and quality, thus affecting the health of the river. One of the essential components for ensuring river health is environmental flow. Nevertheless, the environmental flow is neglected or not appropriately accounted in most of the water management assessments. The objective of this study was to better quantify and assess the environmental flow requirements and developing management practices for ensuring the ecological health of the river. Soil and Water Assessment Tool (SWAT) coupled with a finite element groundwater model, was used for hydrological modelling. The environmental flow regime was evaluated using an index 'Flow Health Score' (FHS), based on a Flow Health Tool. The model was simulated for three conditions – Virgin condition, Managed condition, and Modified condition for Upper and Lower Son separately. Virgin condition assumed no hydraulic interventions, while managed condition incorporated the existing management practices, and modified condition corresponded to the management practices modified in this study for ensuring environmental flow. This approach was demonstrated for the Son River in the Ganga basin. The modelled streamflow agreed with the observed discharge data (R2 = 0.78–0.85). Further, SWAT-FEM coupled model better estimated the low flows than the SWAT model, thus demonstrating the importance of accounting for surface water – groundwater interaction in such environmental flow assessments. Flow health assessment indicated that reservoirs and irrigation diversions have severely affected the high flows in the Upper Son (high flow and highest monthly flow index less than 0.2), and low flows in the Lower Son (low flow index less than 0.2). The model simulation with the modified management practices increased the Flow Health Score (FHS) from 0.4 to 0.6 in Upper Son, and 0.4 to 0.7 in Lower Son. This study showed that coupled SWAT-FEM model, along with the flow health tool, could be effectively used for assessing the in-stream flow requirements and for designing alternative management plans to meet the in-stream flow requirements.

Case Study: Reconstructing the 2015 Dulcepamba River Flood Disaster

ABSTRACT In March 2015, the village of San Pablo de Amalí on the Dulcepamba River in Ecuador was hit by a flood that killed three residents, destroyed five homes, and eroded several hectares of farmland. Residents asserted that the recent construction of a run-of-the-river hydroelectric facility built in the river channel directed flood flows toward the village, causing the associated damage and fatalities. We conducted a forensic hydrologic and hydraulic analysis of the catchment to assess potential causal mechanisms affecting flooding, including the construction of the hydroelectric facility. Hydrologic analysis demonstrated that the river flows produced by the March 2015 storm were equivalent to a 6-year return interval event, with a discharge of 58.6 cms, not the much more extreme 33-year return interval, 400-cms event that had been suggested in a report produced by the hydroelectric company. Hydraulic modeling determined an ∼2-m elevation surcharge of water attributable to the hydroelectric facility, suggesting that damage to the village would not have occurred without the obstruction created by debris blockage of the hydroelectric plant intake. Hydrologic modeling also quantified monthly totals of water availability in the Dulcepamba watershed, including average dry-season flow volumes. When compared to flow volumes allocated to the hydroelectric operator, the modeling indicated that the seasonal water availability in the Dulcepamba watershed is not sufficient to collectively meet the minimum in-stream environmental flow requirements, the agriculture demands from local subsistence irrigators, and the flow volumes allocated to the hydroelectric operator.

Impact of climate change on adaptive management decisions in the face of water scarcity

Reoccurring drought through the early 2000s has caused a serious water scarcity issue in the Colorado River Basin. Previous modeling studies have focused on the impact of climate change without considering the adaptive behaviors of farmers and under-utilized Indian water rights. In this paper, we use a coupled agent-based water resource model (ABM) to investigate how the adaptive decisions of farmers can affect water resource management under both climate change impacts and fully utilized Indian water right conditions. We used five General Circulation Model projections with RCP8.5 scenarios for the study. The results of farm-level decision-making showed different responses in irrigated areas that were changing due to climate change impact. While winter precipitation changes might partially explain the behavior changes, no specific pattern could be concluded based on their location. Also, farmers’ responses about annual water diversion showed more significant inter-year variation compared to irrigated areas. Basin-level metrics showed that climate change impacts will generally worsen water scarcity issues as measured in Navajo Reservoir storage, flow to Lake Powell, and instream flow requirement. But these basin-level water scarcity metrics cannot reflect individual farm-level impacts under climate change, which is why modeling the bottom-up management actions is necessary. When the under-utilized Indian water rights are fully used, it is more likely to trigger the shortage sharing agreement due to the higher tribal water depletion. Evaluation of model uncertainty and a more realistic setup for adaptive actions under drought contingency plans are suggested for future research.

Systems modeling to improve river, riparian, and wetland habitat quality and area

Systems models to improve ecosystems often identify flows to meet minimum instream flow requirements or minimize deviations from a predefined flow regime. Here, we present a new systems optimization model that determines when, where, and how much to allocate scarce water, financial resources, and revegetation efforts to improve aquatic, floodplain, and wetland habitat areas and quality. This optimization is subject to constraints on water mass balance, vegetation growth, infrastructure capacities, and meeting existing agricultural and urban water demands. We followed a participatory approach to apply and validate our model in the Lower Bear River watershed, UT. Results show that increasing winter reservoir releases, minimizing spring spills, and planting native floodplain vegetation early in the growing season can increase suitable habitat area beyond managing water alone. Additional flow on the Little Bear River between August and December will most increase habitat area and quality compared to other locations.

Exploitation of Velocity Gradients by Sympatric Stream Salmonids: Basic Insights and Implications for Instream Flow Management

AbstractHydraulic heterogeneity can strongly influence habitat selection by stream fishes. Velocity gradients created by channel roughness and flow obstructions may be particularly important for species that feed on drifting invertebrates, where maintaining focal points in low‐velocity microhabitats adjacent to faster water allows fish to scan a larger water volume for prey while minimizing swimming costs. However, these velocity gradients are rarely integrated into habitat suitability criteria used for defining instream flow requirements, which are generally based on mean column velocity measurements at the focal point location. It is also unclear how velocity gradient exploitation differs among sympatric drift‐feeding species. We measured the use of velocity gradients by two sympatric juvenile salmonids, Coho Salmon Oncorhynchus kisutch and steelhead O. mykiss, in a midorder cobble–boulder‐dominated river. We compared focal point velocities of fish to adjacent velocities within their foraging area and compared the magnitude of velocity and kinetic energy gradients between species. We then explored how lateral velocity gradients may bias instream flow assessments by deriving two sets of velocity habitat suitability curves (HSCs): conventional HSCs using average water column velocities measured at focal point locations and spatially averaged HSCs incorporating adjacent velocities (four body lengths from focal points). These contrasting HSCs were then used as input into the physical habitat simulation model to predict the influence of flow on habitat availability. Both species often used focal velocities that were lower than adjacent points, but the magnitude of these velocity gradients was higher for steelhead, consistent with known differences in foraging behavior, habitat selection, and physiology. Incorporating adjacent velocities into HSCs resulted in a ~40% (steelhead) and ~10% (Coho Salmon) increase in flows predicted to optimize habitat availability. Thus, small‐scale heterogeneity in velocity used by drift‐feeding fish can lead to large biases in flow assessments.

Hydrological assessment for the availability of water for off-stream uses of Karatoa-Atrai River in Bangladesh

AbstractExplicit consideration of in-stream flow requirement (IFR) has now become almost mandatory in many rivers before irrigation withdrawal is made. Thereby, the primary objective was to evaluate the IFR through hydrological approaches and compare the condition with current flow variability and trends. Flow records were collected from five discharge stations for IFR estimation. Performance of the river was also judged with respect to nine hydraulic cross-sectional data and stage data of ten water-level monitoring stations of Bangladesh Water Development Board (BWDB). Results show that since 2000, the upper Karatoa was able to meet IFR, but the lowest part of the river experienced severe deterioration in addressing its dry season functionality. Also, the decreasing trend in off-stream availability is recognized as a threat to the Singra site resulting from severe aggradations of the river beds. Attention to the less off-stream availability at Singra raises concerns over sustaining the river from drying out. It is now evident that a hydrological approach of IFR is more than just an initial rough estimate. Such a precautionary method works well to provide quick technical support and decision reference for a complex system, in particular, to find specific drying out parts of a river of concern.

Assessing the environmental benefits of multi-purpose water uses of hydropower reservoirs on the Han River in South Korea

The South Korean Government is trying to implement multi-purpose water uses of six hydropower reservoirs on the Han River to strengthen the linkage between water and energy. The expected environmental improvements are an improvement in flood control, an increase in the water supply for environmental improvement, an increase in the water supply for the instream flow requirement, and the abatement of air pollutants and greenhouse gas emissions. This article aims to value the four improvements by applying a choice experiment. For the purpose of reflecting the preference heterogeneity, by investigating the choice experiment data gathered from a survey of 1000 people, a Bayesian estimation of a mixed logit model is employed. The environmental benefits of a 1% improvement in flood control, a 1% increase in the water supply for environmental improvement, a 1% increase in the water supply for the instream flow requirement, and a 1% abatement of air pollutants and greenhouse gas emissions are estimated to be KRW 71 (USD 0.06), 51 (0.05), 28 (0.03), and 77 (0.07), respectively, per household per year. The expected improvements for the four attributes are 25.2%, 17.7%, 17.7%, and 1.0%, respectively. Thus, the expected environmental benefits are worth KRW 3265 (USD 2.96) per household per year and the national value amounts to KRW 63.74 billion (USD 57.77 million).

Agricultural Water Policy during Drought: A Strategy for Including Groundwater Permits in Future Irrigation Buyout Auctions in the Flint River Basin

Georgia’s Flint River Basin has water management challenges from extensive groundwater pumping for agriculture and in-stream flow requirements. The state has experimented with buying out irrigation permits through auctions. Past auctions were relegated to surface water permits. Recently, the state has allowed groundwater permit holders to participate in future auctions. The Flow-Impact Offer (FIO) developed in this paper provides a way to reconcile the disparate impacts of groundwater and surface water withdrawals on in-stream flows when comparing offers in a buyout auction. The techniques suggested here to operationalize the FIO are applicable to other regions of the world as well.

Model-Based Evaluation of the Effects of River Discharge Modulations on Physical Fish Habitat Quality

The increase in minimum flows has rarely been considered to mitigate the ecological impact of hydroelectric power plants because it requires a site-specific design and expensive long-term monitoring procedure to identify the most beneficial scenario. This study presents a model-based method to estimate, within the model constraints, the most sustainable scenario of water resource sharing between nature and human needs. We studied physical habitat suitability of the Isar River in Munich (Germany) for three protected fish species: Thymallus thymallus L., Hucho hucho L., and Chondostroma nasus L. The analysis combined a high-resolution two-dimensional (2D) hydromorphological model with expert-based procedures using Computer Aided Simulation Model for Instream Flow Requirements (CASiMIR). We simulated a range of minimum discharges from 5 to 68.5 m³/s and four scenarios: (A) maximum use of the resource for humans; (B) slight increase in the minimum water flow; (C) medium increase in the minimum water flow; and, (D) without diversion for hydroelectric production. Under the current hydromorphological conditions, model outputs showed that different life stages of the fish species showed preferences for different scenarios, and that none of the four scenarios provided permanently suitable habitat conditions for the three species. We suggest that discharge management should be combined with hydromorphological restoration actions to re-establish parts of the modified channel slope and/or parts of the previously lost floodplain habitat in order to implement a solution that favors all species at the same time. The modeling procedure that is presented may be helpful to identify the discharge scenario that is most efficient for maintaining target fish species under realistic usage conditions.

Ecological Drought: Accounting for the Non-Human Impacts of Water Shortage in the Upper Missouri Headwaters Basin, Montana, USA

Water laws and drought plans are used to prioritize and allocate scarce water resources. Both have historically been human-centric, failing to account for non-human water needs. In this paper, we examine the development of instream flow legislation and the evolution of drought planning to highlight the growing concern for the non-human impacts of water scarcity. Utilizing a new framework for ecological drought, we analyzed five watershed-scale drought plans in southwestern Montana, USA to understand if, and how, the ecological impacts of drought are currently being assessed. We found that while these plans do account for some ecological impacts, it is primarily through the narrow lens of impacts to fish as measured by water temperature and streamflow. The latter is typically based on the same ecological principles used to determine instream flow requirements. We also found that other resource plans in the same watersheds (e.g., Watershed Restoration Plans, Bureau of Land Management (BLM) Watershed Assessments or United States Forest Service (USFS) Forest Plans) identify a broader range of ecological drought risks. Given limited resources and the potential for mutual benefits and synergies, we suggest greater integration between various planning processes could result in a more holistic consideration of water needs and uses across the landscape.

Water Resource Planning Under Future Climate and Socioeconomic Uncertainty in the Cauvery River Basin in Karnataka, India.

Decision‐Making Under Uncertainty (DMUU) approaches have been less utilized in developing countries than developed countries for water resources contexts. High climate vulnerability and rapid socioeconomic change often characterize developing country contexts, making DMUU approaches relevant. We develop an iterative multi‐method DMUU approach, including scenario generation, coproduction with stakeholders and water resources modeling. We apply this approach to explore the robustness of adaptation options and pathways against future climate and socioeconomic uncertainties in the Cauvery River Basin in Karnataka, India. A water resources model is calibrated and validated satisfactorily using observed streamflow. Plausible future changes in Indian Summer Monsoon (ISM) precipitation and water demand are used to drive simulations of water resources from 2021 to 2055. Two stakeholder‐identified decision‐critical metrics are examined: a basin‐wide metric comprising legal instream flow requirements for the downstream state of Tamil Nadu, and a local metric comprising water supply reliability to Bangalore city. In model simulations, the ability to satisfy these performance metrics without adaptation is reduced under almost all scenarios. Implementing adaptation options can partially offset the negative impacts of change. Sequencing of options according to stakeholder priorities into Adaptation Pathways affects metric satisfaction. Early focus on agricultural demand management improves the robustness of pathways but trade‐offs emerge between intrabasin and basin‐wide water availability. We demonstrate that the fine balance between water availability and demand is vulnerable to future changes and uncertainty. Despite current and long‐term planning challenges, stakeholders in developing countries may engage meaningfully in coproduction approaches for adaptation decision‐making under deep uncertainty.

Uncertainty in minimum instream flow requirements for streams in semi-arid environments

Uncertainty in minimum instream flow requirements for streams in semi-arid environments

The Irrigation Effect: How River Regulation Can Promote Some Riparian Vegetation

River regulation impacts riparian ecosystems by altering the hydrogeomorphic conditions that support streamside vegetation. Obligate riparian plants are often negatively impacted since they are ecological specialists with particular instream flow requirements. Conversely, facultative riparian plants are generalists and may be less vulnerable to river regulation, and could benefit from augmented flows that reduce drought stress during hot and dry periods. To consider this 'irrigation effect' we studied the facultative shrub, netleaf hackberry (Celtis reticulata), the predominant riparian plant along the Hells Canyon corridor of the Snake River, Idaho, USA, where dams produce hydropeaking, diurnal flow variation. Inventories of 235 cross-sectional transects revealed that hackberry was uncommon upstream from the reservoirs, sparse along the reservoir with seasonal draw-down and common along two reservoirs with stabilized water levels. Along the Snake River downstream, hackberry occurred in fairly continuous, dense bands along the high water line. In contrast, hackberry was sparsely scattered along the free-flowing Salmon River, where sandbar willow (Salix exigua), an obligate riparian shrub, was abundant. Below the confluence of the Snake and Salmon rivers, the abundance and distribution of hackberry were intermediate between the two upstream reaches. Thus, river regulation apparently benefited hackberry along the Snake River through Hells Canyon, probably due to diurnal pulsing that wets the riparian margin. We predict similar benefits for some other facultative riparian plants along other regulated rivers with hydropeaking during warm and dry intervals. To analyze the ecological impacts of hydropeaking we recommend assessing daily maxima, as well as daily mean river flows.

Proposing environmental flows based on physical habitat simulation for five fish species in the Lower Duero River Basin, Mexico

Background. The concept of “environmental flow” is defined as hydrologic regimes that are required to sustain ecosystem health and functions in rivers. In Mexico, it has become an important topic, not least because a 2012 legal standard (NMX-AA-159-SCFI-2012), establishes procedures for determining instream flow requirements. Goals. The aim of this paper is to propose an acceptable environmental flow requirement for a regulated river segment in the Duero River Basin in, Michoacan, Mexico. Methods. Of the many methods of establishing environmental flows in rivers, this article is concerned with the habitat simulation method. This is based on the IFIM theoretical framework and the PHABSIM mathematical model, by which the WUA-Q curves were obtained for five species of fish. Results . From these curves, we determined that the Goodea atripinnis species has the greater habitat area and reached a maximum of 4338 m2/km for a flow of 5 m3/s; Alloophorus robustus maintained a constant habitat of 2000 m2/km between flow rates of 5 to 15 m3/s. With smaller area, Menidia jordani had a maximum habitat of 1323 m2/km for 4.5 m3/s; and with WUA less than 500 m2/km the curves of the species Algansea tincella and Aztecula sallaei were obtained. Conclusions. The average regulation in March and April was 3.61 and 3.44 m3/s and with the EFR proposal it was 5.11 and 5.00 m3/s for March and April, respectively. In general, the monthly environmental regime is to maintain 80% of the natural flow regime, generating an increase in habitat during the dry season of 24% for A. robustus and 23% for A. sallaei.

Assessment of ecological instream flow requirements under climate change Pseudorasbora parva

Climate change alters ecohydrological processes on different temporal and spatial scales. The aim of this study was to estimate ecological instream flow requirements (EIFR) under climate change impacts and to ascertain optimum flow magnitude to maintain the health of river ecosystems. We used the Mann–Kendall test, the River2D Hydrodynamic model, and the frequency-weighted usable area (FWUA) model on an annual scale in the Juma River to investigate changes in EIFRs caused by climate change. Findings indicated that: (1) between 1956 and 2005, annual instream flow in the Juma River exhibited an abrupt downward trend (in 1981); (2) variation in instream flow governed the area of available fish habitat, and degrees of change for low flow threshold values and low and high FWUA threshold almost exclusively occurred in descending sequential order from winter, spring, autumn, and summer; (3) changes in hydrological regimes influenced both the quantity and quality of physical habitat area, contributing greater to quality than to the distribution of area of physical habitat for Pseudorasbora parva. Climate change, reflected in the changes in EIFR and the area of optimum physical habitat, has dramatically influenced ecological structure and function, even in the small river system investigated for this study. Findings indicated that more rational measures should be put into practice to help address climate change.