Annual Flow Regime Research Articles

The effect of the Almalyk-Akhangaran industrial zone on changes in the groundwater level of the Ahangaran river basin

This article describes the state of groundwater and surface waters in the Akhangaran River basin, around the Almalyk Mining and Metallurgical Combine (AMMC), the amount of water consumed by the population of the city of Almalyk, the amount of precipitation in the region, and the annual flow regime of existing canals in the region. Comprehensive research methods, include the analysis of scientific and technical information on the geographical, hydrogeological, geomechanical and mineralogical compositions of the Almalyk-Akhangaran industrial zone, underground and surface waters, as well as the study of all valuable components by chemical, and X-ray structural methods, and atomic emission spectroscopy. Integration and point methods are used for measuring current velocity. Basic, detailed, abbreviated and graphical methods for measuring water flow are perfomed by electric metrs. Experimental filtration studies are carried out and systems of observation wells are organized. Additionally water temperature is measured with thermocouples and water density, salt concentration and water pH are measured using ionomers.

Streamflow responses to forest and climate change in the boreal Da Hinggan Mountains, Northeastern China

AbstractBoreal forests cover vast stretches of land across all continents and represent a principal source area of clean water in the northern hemisphere. Increasingly, studies are conducted on the impact of changes in boreal forest cover on water yield; however, much remains unknown concerning the effects of forest structure changes on stream discharge over the course of multi‐decadal forest harvest cycles. In this study, we analysed long‐term hydrometeorological and forest dynamics data spanning from 1990 to 2016 from a typical boreal forest watershed in the Da Hinggan Mountains in northern China. Our objective was to quantify how changes in forest age and tree species composition affect mean annual streamflow and flow regimes in the context of a changing climate. To distinguish the effects of forest and climate changes on annual streamflow from one another, we employed a combination of a sensitivity‐based method and a temporal trend analysis. Further, we evaluated the impact of forest changes on flow regimes using four indicators: magnitude, duration, frequency, and variability. The results indicated that mean annual streamflow increased by 55.8 mm, with forest changes contributing +61.4 mm compared to −5.6 mm due to climate change (negative effect). This increase occurred when approximately 20% of mature coniferous forests transitioned to mid‐age broad‐leaved forests, accompanied by a 10% increase in total stock volume during the later period. Finally, the effect of changes in forest structure on flow regime were not significant. Our results underscore that variations in forest structure affect streamflow differently depending on stand age and species proportions. Therefore, dynamic forest structure management can benefit not only carbon sequestration but also water supply capacity in boreal forested watersheds.

Assessment of upbasin dam impacts on streamflow at Chiang Saen gauging station during the period 1960–2020 in the context of statistical studies

The Langcang-Mekong River Basin is the most important transboundary river basin in Asia. However, over the recent decades, dam construction has had increasingly profound effects on hydrological processes and aquatic, particularly riparian, ecosystems. Understanding these impacts is critical for the foundation of sustainable runoff surface management. In this study, different methods, based on both graphical and statistical techniques, were applied to assess the effects of the dams on annual, seasonal and monthly runoff and to detect hydroclimatic trends in the Upper Mekong Basin during the period 1960–2020. The results reveal two change points with respect to seasonal and annual flow regimes; that is, 2003 for the flood season and annual flows and 2013 for the dry season flow. The duration of the flood season and the volume of annual discharges have both significantly decreased since 2003 and the dry season discharge has significantly increased since 2013 (with both p-values <.05). The quantitative assessment suggests that, due to the effect of dams, the monthly discharges increased by 10–450 m3/s during the dry season (December–May), while the flood season's monthly flows decreased significantly, by 1,028–2,150 m3/s, from July to October at Chiang Saen station. The study of hydrological changes in the Mekong watershed is expected to be a significant contribution towards a better understanding of large watersheds in which the hydrological effects are influenced not only by climate change at large spatial and temporal scales but also by changes in the physical environment due to the construction of dams.

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.

Reservoir fertilisation and fishery response in a highly managed reservoir with uncertain flows: Ecosystem‐based management using decision analysis

AbstractInland fisheries managers must account for multiple competing uses for aquatic resources; using methods such as ecosystem‐based management allows for different priorities for aquatic ecosystems to be accounted for. Declining abundance of kokanee salmon Oncorhynchus nerka (Walbaum) in Arrow Lakes Reservoir in the 1990s led to the use of large‐scale nutrient addition to improve productivity of kokanee and large piscivores. However, it is unclear what effect these measures had on the system given high discharge and highly variable annual flow regime throughout the watershed. An Ecopath with Ecosim model of the ecosystem was fitted to the available data and used to predict ecosystem structure and reservoir objectives under different nutrient addition strategies and varying annual flow regimes. Results from the model indicate that nutrient addition is an important driver in the system, with lower flows resulting in higher biomass for higher trophic levels. Decision analysis demonstrated the importance of maintaining nutrient additions to achieve management objectives despite losses in some high‐flow years.

Bed Particle Displacements and Morphological Development in a Wandering Gravel‐Bed River

AbstractBed particles were tracked using passive integrated transponder tags in a wandering reach of the San Juan River, British Columbia, Canada, to assess particle movement around three major bars in the river. In‐channel topographic changes were monitored through repeat LiDAR surveys during this period and used in concert with the tracer data set to assess the relationship between particle displacements and changes in channel morphology, specifically, the development and re‐working of bars. This has direct implications for virtual velocity and morphologic based estimates of bedload flux, which rely on accurate estimates of the variability and magnitude of particle path lengths over time. Tracers were deployed in the river at three separate locations in the Fall of 2015, 2016, 2017, and 2018, with recovery surveys conducted during the summer low‐flow season the year after tracer deployment and multiple mobilizing events. Tracers exhibited path length distributions reflective of both morphologic controls and year to year differences related to the annual flow regime. Annual tracer transport was restricted primarily to less than one riffle‐pool‐bar unit, even during years with a greater number of peak floods and duration of competent flow. Tracer deposition and burial was focused along bar margins, particularly at or downstream of the bar apex, reflecting the downstream migration and lateral bar accretion observed on Digital Elevation Models of difference. This highlights the fundamental importance of bar development and re‐working underpinning bedload transport processes in bar‐dominated channels.

A hydrologic feature detection algorithm to quantify seasonal components of flow regimes

Seasonal flow transitions between wet and dry conditions are a primary control on river conditions, including biogeochemical processes and aquatic life-history strategies. In regions like California with highly seasonal flow patterns and immense interannual variability, a rigorous approach is needed to accurately identify and quantify seasonal flow transitions from the annual flow regime. Drawing on signal processing theory, this study develops a transferable approach to detect the timing of seasonal flow transitions from daily streamflow time series using an iterative smoothing, feature detection, and windowing methodology. The approach is shown to accurately identify and characterize seasonal flows across highly variable natural flow regimes in California. A quantitative error assessment validated the accuracy of the approach, finding that inaccuracies in seasonal timing identification did not exceed 10%, with infrequent exceptions. Results for seasonal timing were also used to highlight the statistically distinct timing found across streams with varying climatic drivers in California. The proposed approach improves understanding of spatial and temporal trends in hydrologic processes and climate conditions across complex landscapes and informs environmental water management efforts by delineating timing of seasonal flows.

Stay with the flow: How macroinvertebrate communities recover during the rewetting phase in Alpine streams affected by an exceptional drought

AbstractDroughts are affecting an increasing number of lotic ecosystems worldwide due to the combined effects of climatic and anthropogenic pressures. Unlike naturally intermittent rivers, where the drying phase is a part of the annual flow regime, water scarcity in Alpine rivers represents a relatively recent phenomenon and, therefore, a major threat for the biodiversity of these lotic ecosystems. However, Alpine stream community response to drought is still poorly investigated. Here, we assess the recovery of macroinvertebrates in two Alpine streams after a supraseasonal drought. As water returned, a total of 10 sampling sessions were carried out, and temporal patterns in diversity, density, and taxonomic composition of benthic communities, as well as in the percentage of functional feeding groups, were investigated.We found that the resistance of invertebrate communities in Alpine streams is generally low: drought markedly reduced the diversity and density of macroinvertebrates. Conversely, our results suggest that the passive dispersal by drift from the upstream river sections seems the most probable mechanism promoting the post‐drought recovery. Nevertheless, this resilience ability appears to be stream specific and influenced by intrinsic stream characteristics, including the flow permanence and distance from the nearest upstream perennial reach. This work sheds light on the ecological consequences of droughts on macroinvertebrate communities. As flow intermittency in Alpine areas is expected to intensify under current global change scenarios, results of this study provide important information to predict changes in the taxonomic composition and diversity of macroinvertebrate communities.

A power market-based operation support model for sub-daily hydropower regulation practices

With increasing power production from renewable energy sources, sub-daily variations in energy demand need to be balanced. Today, hydropower is commonly used as balancing power. In this study, we quantified the impact of capacity constraints, in terms of reservoir volume and hydropower capacity, on the potential to comply with instant energy demand. To evaluate the impact, we developed two new metrics, power market impact and system efficiency ratio, which are based on two threshold flow regimes derived from natural flow as lower threshold release and regulated flow (based on hourly energy prices) as upper threshold release. The operation support model comprises 96 different regulation scenarios based on varying combinations of hydropower and reservoir capacities. For each scenario, an hourly water balance was simulated, to obtain the highest complying with upper threshold release based on actual energy demand. We tested the framework on the Kemijoki river with defined thresholds based on the natural flow regime (tributary river Ounasjoki) and the hourly energy price in Finland in 2017, and estimated the impact of regulation on hourly flow regime at the Taivalkoski hydropower station. The annual flow regime impact in 2013, 2014 and 2015 was estimated to be 74%, 84% and 61%, respectively, while the monthly impact varied from 27% to 100%. Our framework for evaluating interactions between the power market and sub-daily regulation practices is a useful novel tool for sustainable river management and can be easily applied to different rivers and regions and evaluated for different timescales.

Dynamic contributions of intermittent and perennial streams to fish beta diversity in dryland rivers

AbstractAimTo determine the role of flow intermittence and species origin in shaping freshwater fish beta diversity across dryland riverscapes.LocationVerde and Little Colorado River basins, United States.MethodsFish beta diversity was investigated in two large rivers with marked differences in basin‐wide flow intermittence. Local site (continually flowing perennial vs. periodically flowing intermittent) and species (native vs. non‐native) contributions to beta diversity were compared within each basin and over multiple decades (1987–2013) in relation to changing hydrologic conditions. Metacommunity dynamics were quantified using changes in alpha‐ (local), beta‐ and gamma‐ (regional) diversity through time.ResultsBeta‐diversity patterns varied in relation to basin‐wide intermittence. Intermittent sites were most influential to beta diversity where basin‐wide intermittence was lower (Verde River), whereas perennial sites were most influential where basin‐wide intermittence was higher (Little Colorado River). In intermittent sites, native fish species contributions to beta diversity tended to be higher than non‐native species contributions. The relative contributions of perennial and intermittent sites to β‐diversity within each basin were invariant to annual flow regimes, whether atypically lower or higher than average flows, but somewhat related to intra‐annual flow variation. Native species contributions to β‐diversity increased in years with high flow conditions in the Verde River. Over time, beta diversity decreased in the lower intermittence Verde River, indicating taxonomic homogenization, but remained relatively unchanged in the Little Colorado River.Main ConclusionsInvestigations of beta‐diversity components over time are considered pivotal for conservation prioritization and planning. We found that both intermittent and perennial streams play complementary roles in supporting fish beta diversity, and that their relative contributions increase as basin wide availability of the habitat type decreases. Moreover, contributions of intermittent streams to overall beta diversity were relatively consistent through time and supported native fish diversity. Despite weakening policy protections of intermittent streams, these habitats are critical for supporting local species persistence and regional biodiversity.

Water Yield Responses to Gradual Changes in Forest Structure and Species Composition in a Subboreal Watershed in Northeastern China

Relationships between forest cover and streamflow have been studied worldwide, but only a few studies have examined how gradual changes in forest structure and species composition due to logging and climate change affect watershed water yield (Q) and flow regimes. In this study, we analyzed long-term (45 years) hydrologic, climate and forest dynamics data from the subboreal Tahe watershed in northeastern China. Our purpose was to evaluate the effects of forest logging and regeneration on changes in forest biomass and species and to quantify the subsequent impact on mean annual streamflow and flow regime under a changing climate. The study watershed was dominated by old-growth larch (Larix gmelinii Rupr.) during the 1970s, but gradually transformed into young deciduous larch mixed with deciduous broad-leaved birch (Betula platyphylla Sukaczev) during the 2010s. During the same period, the watershed experienced climate change with a significant increase in air temperature of 0.028 ℃/year. We applied eight sensitivity-based techniques to separate the effects of climate change on water yield from those due to forest changes. We used flow duration curves (FDCs) to characterize flow regimes by dividing the study into four key periods based on the proportional change of larch and birch trees. We found that the mean annual streamflow decreased by 10 mm (−16 mm attributed to forest change and +6 mm to climate change) between the 1984–1994 period and the 2006–2016 period when the proportion of birch increased by 20% with a similar total forest volume in the later period. The mean annual streamflow increased from 216 mm to 270 mm (+35.5 mm due to forest change vs +17.7 mm due to climate change) when forest volume decreased by 18.7% (17 m3/ha) between the 1970s and 1984–1994. Water yield changed only slightly (3.5 mm) when forest volume increased by 8.7% (6 m3/ha) from 2000 to 2011. In addition, the magnitude of high flow and low flow increased following deforestation and a shift in species composition from a period (1984–1994) with 70% larch with 30% birch to a later period (2006–2016) with 50% larch with 50% birch. Both high flow and low flow decreased coinciding with a reforestation period (2006–2016). Our results highlight complex interactions among climate, forest structure, total biomass, and plant diversity (trees species composition) in influencing watershed hydrology. Further study is needed to examine the effects of ecohydrological processes such as evapotranspiration in larch and birch forests on hydrologic changes across multiple scales.

Assessment of Climate Driven Changes in Flow Series of Alpine Basin: A Case Study of Danube River Basin

This study was carried out in order to analyze the climate change driven influence on mean monthly flow series of Danube River and its tributaries during the last century. The study confirms some signs of climate driven alterations in monthly river flow series along with change in flow seasonality during the last century. In spite of this, man-made interference in the basin like i.e. groundwater extraction, irrigation, river regulation, land use alteration and urbanization, has significantly changed Danube flow regime in most areas of the catchment. The analysis of Achleiten station demonstrates that average annual flow regime is a little bit increased. Major increase is observed in winter and autumn months and decrease in summer months. These seasonal alterations clearly signal a future glimpse of reduced water availability in alpine basins. This will mainly occur due to the change in the form of precipitation in winter, from snow to rain and the consequent less snow accumulation, and the early melt of snow storage, less precipitation and high evaporation rate in summer.

Trend analysis of nutrient loadings in a large prairie catchment

ABSTRACTNutrient loadings in many river catchments continue to increase due to rapid expansion of agriculture, urban and industrial development, and population growth. Nutrient enrichment of water bodies has intensified eutrophication which degrades water quality and ecosystem health. In this study, we carried out a trend analysis of total phosphorus and total nitrogen loads in the South Saskatchewan River (SSR) catchment using a novel approach to analyse nutrient time series. Seasonal analysis of trends at each of the water quality stations was performed to determine the relationships between annual flow regimes and nutrient loads in the catchment, in particular, the influence of the high spring runoff on nutrient export. Decadal analysis was also performed to determine the long-term relationships of nutrients with anthropogenic changes in the catchment. Although it was found that seasonal and historical variability of nutrient load trends is mainly determined by streamflow regime changes, there is evidence that increases in nitrogen concentration can also be attributed to anthropogenic changes.

Trend analysis of nutrient loadings in a large prairie catchment

ABSTRACTNutrient loadings in many river catchments continue to increase due to rapid expansion of agriculture, urban and industrial development, and population growth. Nutrient enrichment of water bodies has intensified eutrophication which degrades water quality and ecosystem health. In this study, we carried out a trend analysis of total phosphorus and total nitrogen loads in the South Saskatchewan River (SSR) catchment using a novel approach to analyse nutrient time series. Seasonal analysis of trends at each of the water quality stations was performed to determine the relationships between annual flow regimes and nutrient loads in the catchment, in particular, the influence of the high spring runoff on nutrient export. Decadal analysis was also performed to determine the long-term relationships of nutrients with anthropogenic changes in the catchment. Although it was found that seasonal and historical variability of nutrient load trends is mainly determined by streamflow regime changes, there is evide...

Biogeophysical properties of an expansive Antarctic supraglacial stream

AbstractSupraglacial streams are important hydrologic features in glaciated environments as they are conduits for the transport of aeolian debris, meltwater, solutes and microbial communities. We characterized the basic geomorphology, hydrology and biogeochemistry of the Cotton Glacier supraglacial stream located in the McMurdo Dry Valleys of Antarctica. The distinctive geomorphology of the stream is driven by accumulated aeolian sediment from the Transantarctic Mountains, while solar radiation and summer temperatures govern melt in the system. The hydrologic functioning of the Cotton Glacier stream is largely controlled by the formation of ice dams that lead to vastly different annual flow regimes and extreme flushing events. Stream water is chemically dilute and lacks a detectable humic signature. However, the fluorescent signature of dissolved organic matter (DOM) in the stream does demonstrate an extremely transitory red-shifted signal found only in near-stream sediment leachates and during the initial flushing of the system at the onset of flow. This suggests that episodic physical flushing drives pulses of DOM with variable quality in this stream. This is the first description of a large Antarctic supraglacial stream and our results provide evidence that the hydrology and geomorphology of supraglacial streams drive resident microbial community composition and biogeochemical cycling.

Comparing flow regime, channel hydraulics, and biological communities to infer flow–ecology relationships in the Mara River of Kenya and Tanzania

Equatorial rivers of East Africa exhibit unusually complex seasonal and inter-annual flow regimes, and aquatic and adjacent terrestrial organisms have adapted to cope with this flow variability. This study examined the annual flow regime over the past 40 years for three gauging stations on the Mara River in Kenya and Tanzania, which is of international importance because it is the only perennial river traversing the Mara-Serengeti ecoregion. Select environmental flow components were quantified and converted to ecologically relevant hydraulic variables. Vegetation, macroinvertebrates, and fish were collected and identified at target study sites during low and high flows. The results were compared with available knowledge of the life histories and flow sensitivities of the riverine communities to infer flow–ecology relationships. Management implications are discussed, including the need to preserve a dynamic environmental flow regime to protect ecosystems in the region. The results for the Mara may serve as a useful model for river basins of the wider equatorial East Africa region.Editor Z.W. Kundzewicz; Guest editor M. AcremanCitation McClain, M.E., Subalusky, A.L., Anderson, E.P., Dessu, S.B., Melesse, A.M., Ndomba, P.M., Mtamba, J.O.D., Tamatamah, R.A., and Mligo, C., 2014. Comparing flow regime, channel hydraulics and biological communities to infer flow–ecology relationships in the Mara River of Kenya and Tanzania. Hydrological Sciences Journal, 59 (3–4), 801–819.

Influence of hydrological regime on wetland attenuation of diffuse agricultural nitrate losses

A simple first-order dynamic model that accounts for hydrology, nitrate concentrations, internal hydraulic efficiency and water temperature was used to evaluate the influence of influent hydrological regimes on nitrate-N removal performance in surface-flow wetlands. The model, run using hourly hydrological and climatic data for a wetland treating subsurface tile drainage, was able to closely simulate flow-proportional nitrate-N concentrations recorded at the wetland outlet. Applying the model to 7 different annual flow regimes showed substantial year-to-year differences in predicted percentage and mass nitrate-N removal performance. Predicted areal mass removal rates declined markedly as wetland size was increased from 0.5 to 5% of contributing catchment, illustrating the diminishing returns achievable and the performance limits of wetland treatment receiving highly variable diffuse flows. Doubling the wetland size from 1% to 2% of contributing catchment provided about 75% increase in performance, but doubling from 2% to 4% of catchment area only provided about 43% further improvement. Large wetland areas occupying 5% of contributing catchment were predicted on average to be able to remove a maximum of 55% of the nitrate-N loads delivered, with removal expected to range between 40 and 70% of the nitrate-N load from year-to-year depending primarily on the flow regime. Application of the model to equivalent wetlands receiving normalised stream flows (same nitrate-N concentration, total flow and load) from up- and down-stream sites in two catchments with contrasting flow regimes predicted substantially better overall performance when flows were steady or exhibited low variability. With increasing flow variability predicted wetland nitrate-N removal efficiency was reduced by 5–14 and 13–21 percentage points for wetlands occupying 1 and 4% of catchment area, respectively. We conclude that flow regime is likely to be a key factor influencing the nitrate-N removal performance of surface-flow wetlands receiving diffuse flows from agricultural catchments. Seasonal patterns and variability of flow need to be seriously considered when assessing expected performance, and in optimising the location and design of wetlands for diffuse pollution management.

Variable-source flood pulsing in a semi-arid transboundary watershed: the Chobe River, Botswana and Namibia

The Chobe River, characterized by an unusual flood pulsing regime and shared between Botswana and Namibia, lies at the heart of the world's largest transfrontier conservation area (the Kavango-Zambezi Transfrontier Conservation Area). Significant ecological changes and vegetation conversions are occurring along its floodplains. Various scenarios for agricultural and urban water use are currently being proposed by the government of Botswana. However, the understanding of the river's annual flow regime and timing of the relative contributions of water from three different sources is relatively poor. In light of past and future climate change and variability, this means that allocating water between ecological flows and economic and domestic uses will become increasingly challenging. We reconstruct the inundation history in this basin to help ease this challenge. This paper presents a spatiotemporal approach to estimate the contribution of water from various sources and the magnitude of changes in the flooding extent in the basin between 1985 and 2010. We used time series analysis of bimonthly NOAA AVHRR and NASA MODIS data and climatologic and hydrologic records to determine the flooding timing and extent. The results indicate that between 12 and 62% of the basin is flooded on an annual basis and that the spatial extent of the flooding varies throughout the year as a function of the timing of peak discharge in two larger basins. A 30-year trend analysis indicates a consistent decline in the average monthly flooded area in the basin. The results may prove useful in future water utilization feasibility studies, in determining measures for protecting ecological flows and levels, and in ecosystem dynamics studies in the context of current and future climate change and variability.

Regional classification, variability, and trends of northern North Atlantic river flow

AbstractRegional classification techniques can help in identifying spatial structure in river flow variation. As such, a framework can be provided around which to test hypotheses, making regional classification an important tool for hydrological research, particularly over large and complex geographical domains. Here, the results of a regional classification of monthly river flow for the northern North Atlantic region over the period 1968–1997 are presented. Importantly, regional classes are identified on the basis of inter‐annual variation in river flow time series, rather than the more commonly used intra‐annual flow regime. This is beneficial because it provides an improved basis for the investigation of regional‐scale inter‐annual trends in river flow: an important aim given the potential for future changes in river discharge linked to climate change and land‐use change. Seven regions (four in northern Europe and three in eastern North America) are identified using hierarchical cluster analysis (Wards algorithm). Analysis of the hydrological homogeneity of the emergent river flow regions reveals them to be useful groupings to frame further analyses. Investigation of the statistical characteristics of each mean regional time series follows, including the annual flow regime, time series variability, and the presence of trends (as indicated by the Mann‐Kendall test). Key findings identified by the latter analysis include an increasing trend in late winter discharge for some northern European regions for 1968–1997, but overall few statistically significant trends. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Relative impact of anthropogenic modifications versus climate change on the natural flow regimes of rivers in the Northern Rocky Mountains, United States

We studied discharge data from stream gauges located in natural and anthropogenically modified river basins of the Northern Rocky Mountains over 59 years. We applied linear and nonlinear models to the data to determine what, if any, alterations have occurred in the annual flow regimes. By comparing the different results from the natural and anthropogenically modified river basins, we were able to distinguish the impacts that climate change and anthropogenic modifications have had on flow regimes in the Northern Rocky Mountains over the period of record. We found that regional climate change has not significantly altered the natural flow regimes. However, we did find an underlying cyclical pattern in the total amount of annual discharge in both the natural and anthropogenically modified river basins. This suggests a strong link between the quantity of runoff and some kind of hydroclimatologic cycle. Conversely, direct basin anthropogenic modifications such as damming, irrigation, and urbanization have caused a decrease in the difference between the minimum and maximum annual discharges and a decrease in the daily variations of flows across the Northern Rocky Mountains. In general, direct anthropogenic modifications of the river basins have altered the flow regimes to a much greater extent than climate change.