Streamflow Regime Research Articles

Influence of changes in land use and land cover and rainfall on the streamflow regime of a watershed located in the transitioning region of the Brazilian Biomes Atlantic Forest and Cerrado.

Climate change and the intensification of anthropogenic activities in watersheds have been substantially changing the streamflow regime, which is a problem for water resource managers. This study assesses the influence of the changes in land use and land cover and rainfall on the streamflow regime. This study also models the pattern of these streamflows according to the rainfall and land use and land cover in the Santo Antônio River watershed, located in the transitioning region of the Brazilian Biomes Atlantic Forest and Cerrado. To assess the dynamic relationship between land use and land cover and the streamflow regime, five classes of land use and land cover were used. To characterize the hydrological pattern, data from six streamflow gauges and 24 rainfall gauges that influence the study area were used. Multiple regression models were adjusted to estimate streamflow using the explanatory variables rainfall and land use and land cover. As result, a direct relationship was found, as the decrease in streamflow in some drainage areas was influenced by the decrease in rainfall over the base period. The relationship between land use and land cover and streamflow was not significant. The reductions in the streamflow regimes over the years in the watershed were influenced by reductions in annual rainfall, which reduced about 19% while the water withdrawals from 2003 to 2014 increased 2350%. The results found in this study are useful to the water managers since they can estimate streamflow in any part of the studied river through rainfall and land use and land cover data. This helps to reduce the risks associated with the water allocation process.

Detection and prediction of land use change impact on the streamflow regime in Sahelian river basin, northwestern Nigeria

Abstract Detecting and predicting the impact of land use/land cover (LULC) changes on streamflow are crucial sources of information for the effective management and protection of land and water resources in Sahelian ecosystems such as the Hadejia river basin. In this study, LULC change detection was performed using ENVI, while the LULC modeling was conducted using the cellular automata (CA)–Markov in the IDRISI environment. However, the streamflow trend and variation were assessed using the Mann–Kendall (MK) trend test and the inverse distance weightage (IDW). Before the LULC modeling and projection (2030), the LULC was classified for 1990, 2000, and 2010 using supervised classification. Model output revealed a strong relationship between LULC and streamflow trend, thus, the decade 1990–2000 was the decade with high forest clearance and streamflow output, and consequently severe floods. However, the decade 2000–2010 witnessed land use expansion mainly via construction (3.4%). Meanwhile, the scenario will slightly change in the future as agriculture is projected to expand by about 9.3% from 2010 to 2030 due to the increased human population. Thus, food insecurity aggravated by climate change should be anticipated, and measures to avert/reduce their effects must be initiated.

Impact Of Mozhaysk Dam On The Moscow River Sediment Transport

Sediments are an essential part of the aquatic environment that define its transformation and development. The construction of dams results in severe changes in sediment fluxes. This study aims to assess how the sediment load of the upper Moskva River is affected by the Mozhaysk Dam flow regulation and to estimate its dynamics over the years of the reservoir’s existence. Our analysis of the 1968, 2012 and 2016 detailed field data shows a 20-40% decrease in the proportion of the spring flood in the annual sediment load into the reservoir, which is caused by changes in the streamflow regime of the inflowing rivers. The peak suspended sediment concentrations have decreased 5- to 10-fold, likely due to a significant decline in the watershed’s cultivated land area, which caused a decrease in the erosion rate. In the Moskva River below the dam, the seasonal dynamics of the suspended sediment concentration no longer corresponds to the natural regime. The annual suspended load of the Moskva River below the Mozhaysk Reservoir decreased up to 9-fold. The sediment retention in the reservoir has dropped from 90% to 70-85% and is to some extent restored by an outflow of the particulate organic matter produced in the reservoir. We also described the relationships between water turbidity and suspended sediment concentration of the reservoir’s tributaries, which allow for the first time to estimate the sediment load with higher accuracy than was previously possible.

Climate change will render size‐selective harvest of cold‐water fish species unsustainable in Mediterranean freshwaters

Abstract Climate change is impacting the composition and functioning of virtually every ecosystem on Earth, and disrupting the productivity of exploited ones. Species are rapidly adjusting to their changing environments through evolutionary and/or plastic phenotypic changes in behavioural, physiological, phenological and life‐history traits. Size‐selective harvest produces severe demographic impacts on exploited populations and induces individual phenotypic changes in many of the same fitness‐related traits as climate change and thus can impair local adaptation and acclimation. We addressed in the context of inland recreational fisheries two interrelated questions: (1) Will fisheries‐induced phenotypic changes operate at different rates and direction than those induced by climate change, and thus hinder local adaptation and acclimation, threatening population persistence?; (2) which harvest regulations most likely lead to overexploitation of populations under the new environmental conditions? We used an eco‐genetic individual‐based model to simulate the consequences of size‐selective fishing for a cold‐water fish species brown trout Salmo trutta across a range of regulatory (defined by exploitation rate and size‐based limits) and environmental scenarios (warming vs. concurrent warming and streamflow reduction) in a Mediterranean system. We ran 1,620 combinations of fishing and environmental scenarios and analysed results using artificial neural networks. In our simulations, (a) climate change and size‐selective fishing both led to a reduced, truncated population, with increased juvenile but decreased adult growth and earlier maturation at smaller size, but fisheries‐induced changes were stronger than those produced by climate change; (b) their effects were additive or dampened but rarely synergistic and (c) phenotypic changes in fitness‐related traits resulted from both evolutionary and plastic processes. Synthesis and applications. Our model‐based analyses highlight that any size‐selective fishing regime would lead to the overexploitation of cold‐water freshwater fish populations if climate warming is accompanied by streamflow reduction—as projected in Mediterranean fisheries. Even if we assumed no future streamflow regime changes, only a limited range of size‐based harvest regulations may provide an acceptable balance between conservation and fishery objectives. Thus, recreational fisheries of cold‐water fish in Mediterranean climates might be more sustainably managed under climate change if conservation‐oriented strategies based on harvest bans (e.g. catch‐and‐release fishing) were implemented.

Estimating Surface Water Presence and Infiltration in Ephemeral to Intermittent Streams in the Southwestern US

Streamflow in arid and semi-arid regions is predominantly temporary, an integral part of mountain block hydrology and of significant importance for groundwater recharge and biogeochemical processes. However, temporary streamflow regimes, especially ephemeral flow, remain poorly quantified. We use electrical resistance sensors and USGS stream gauge data in 15 southern Arizona streams spanning a climate gradient (mean annual precipitation from 160 to 750 mm) to quantify temporary streamflow as streamflow presence and water presence, which includes streamflow, ponding and soil moisture. We use stream channel sediment data to estimate saturated hydraulic conductivity and potential annual infiltration. Annual streamflow ranged 0.6–82.4% or 2–301 days; while water presence ranged from 2.6 to 82.4% or 10 to over 301 days, or 4–33 times longer than streamflow. We identified 5 statistically distinct flow regimes based on the annual percent streamflow and water presence: (1) dry-ephemeral, (2) wet-ephemeral, (3) dry-intermittent, (4) wet-intermittent, and (5) seasonally-intermittent. In contrast to our expectations, stream channel density was a better predictor of annual streamflow and water presence than annual rainfall alone. Whereas, the dry-ephemeral and wet-ephemeral flow regimes varied with seasonal precipitation, the dry-intermittent, wet intermittent and seasonally-intermittent flow regimes did not. These results coupled with the potential infiltration estimates indicate that streamflow at the driest sites occurs in response to rainfall and overland flow while groundwater discharge and vadose zone contributions enhance streamflow at the wetter sites. We suggest that on a short temporal scale, and with respect to water presence, wetter sites might be buffered better against shifts in the timing and distribution of precipitation in response to climate change. Flow regime classifications that include both stream flow and water presence, rather than on stream flow alone, may be important for predicting thresholds in ecological functions and refugia in these dryland systems.

Arctic riparian shrub expansion indicates a shift from streams gaining water to those that lose flow

Shrub expansion has been observed across the Arctic in recent decades along with warming air temperatures, but tundra shrub expansion has been most pronounced in protected landscape positions such as floodplains, streambanks, water tracks, and gullies. Here we show through field measurements and laboratory analyses how stream hydrology, permafrost, and soil microbial communities differed between streams in late summer with and without tall shrubs. Our goal was to assess the causes and consequences of tall shrub expansion in Arctic riparian ecosystems. Our results from Toolik Alaska, show greater canopy height and density, and distinctive plant and soil microbial communities along stream sections that lose water into unfrozen ground (talik) compared to gaining sections underlain by shallow permafrost. Leaf Area Index is linearly related to the change in streamflow per unit stream length, with the densest canopies coinciding with increasingly losing stream sections. Considering climate change and the circumpolar scale of riparian shrub expansion, we suggest that permafrost thaw and the resulting talik formation and shift in streamflow regime are occurring across the Low Arctic.

Influence of Climate and Duration of Stream Water Presence on Rates of Litter Decomposition and Nutrient Dynamics in Temporary Streams and Surrounding Environments of Southwestern USA

Ephemeral and intermittent streams are increasing with climate and land use changes, and alteration in stream water presence or flow duration will likely affect litter decomposition and nutrient dynamics in channel and riparian zones more than uplands. To investigate the influence of varying climate and stream flow regimes on rates of decomposition and associated nutrient dynamics, we used a space-for-time substitution design in which we deployed a common leaf litter across a range of ephemeral to seasonally- intermittent stream reaches (10) and landscape positions (channel, riparian, upland) in Arizona, USA over an 18-month period. We also measured soil physio-chemical properties and nutrient dynamics associated with these reaches and positions. Consistent with expectations, rates of litter decomposition (k) decreased significantly in the channels as cumulative percentage (%) of water presence decreased below 40%. Indeed, differences in cumulative duration of water presence as well as channel bed material silt content explained 80% of the variation in k across flow regimes. In contrast, decay rates of the common litter across sites were surprisingly similar in upland and riparian positions despite large differences in climate, specifically precipitation (160-516 mm). Relatively similar litter nitrogen immobilization and soil moisture in upland and riparian environments helped to explain the lack of difference in k and soil nutrient dynamics in these environments. Collectively, our findings indicate that stream water presence may be a more important indicator of ephemeral and intermittent stream function than stream flow alone and that riparian zones in these dryland regions may be less responsive to changes in climate and associated subsidies of stream flow.

Low-flow behavior of alpine catchments with varying quaternary cover under current and future climatic conditions

Alpine environments are particularly vulnerable to climatic warming, and long term observations suggest a shift of snow-influenced river discharge towards earlier periods of the year. For water resources management, the seasonal patterns of discharge in alpine areas are particularly relevant, as the shift to lower flows in summer and autumn combined with increased water demand could lead to water shortage in downstream catchments. The storage of groundwater in alpine catchments could significantly modulate how changing climatic conditions influence the annual streamflow regime. However, groundwater storage and its buffering capacity in alpine areas remain poorly understood. Moreover, studies on how climate change will impact water resources in alpine areas rarely consider the influence of geology.In this paper, catchment geology is used as a basis for the classification of future summer low flows behavior of several alpine catchments in Switzerland. Based on the analysis of the relationship between low-flow indicators and geology, the role of unconsolidated quaternary deposits is explored. We show that quaternary deposits play a critical role in the seasonal storage of groundwater, which can contribute to rivers during low-flow periods. Three climate change simulations based on extreme RCP 8.5 scenarios are fed into a conceptual hydrological model to illustrate the buffering role of groundwater. Past and future low flows normalized by mean past and future streamflows appear correlated with the percentage of unconsolidated quaternary deposits. These results highlight that catchments with high groundwater contribution to streamflow relative to precipitation will have a slower decrease in future summer discharge. Therefore, we propose two indicators that can be used to anticipate the response of future summers low flows in alpine areas to climate change: the current winter low flows and the percentage of unconsolidated quaternary deposits of the catchments.

APPLICABILITY OF THE SWAT HYDROLOGICAL MODEL IN THE MUCURI RIVER BASIN

ABSTRACT Land-use changes promote significant variations in streamflow regimes, and hydrological models allow studying their impacts. Based on this approach, this study aimed to assess the applicability of the SWAT model for different land-use scenarios and their respective impacts on the flow regime of the Mucuri River. The average monthly and daily water balance was generated after the calibration and validation of the SWAT model in the basin. Three land-use scenarios were analyzed in relation to the current land use, as follows: replacement of the agricultural area by the eucalyptus crop, replacement of the native forest area by the sugarcane crop, and replacement of pasture by exposed soil. The results showed that the SWAT model is adequate to simulate the land-use change and its impact on the flow regime of the Mucuri River; the replacement of agriculture by eucalyptus in the basin led to a decrease in the average and minimum reference streamflows; and the replacement of the forest cover by sugarcane and pasture by exposed soil provided an increase in the average and minimum reference streamflows.

Stream Flow Changes and the Sustainability of Cruise Tourism on the Lijiang River, China

Water resources play a critical role in the sustainable development of river-based tourism. Reduced stream flow on the Lijiang River, south China, may negatively impact the development of cruise tourism. We explored the effects of stream flow changes on cruise tourism by determining (1) cruise tourism development indicators, (2) stream flow regime characteristics and their impacts on cruise tourism development indicators, and (3) climate variability and socio-economic factors effecting stream flow. Cruise tourism on the river has experienced rapid growth in recent decades. Stream flow regimes displayed no significant changes between 1960 and 2016, although dry season stream flow was significantly lower than in other seasons. We found that stream flow changes did not have a significant impact on the development of cruise tourism. As precipitation has not changed significantly, policies, including regulated stream flow from hydroelectric reservoirs, are assumed to mitigate reduced stream flow. However, increased irrigation and economic development, combined with future climate change, may increase challenges to cruise tourism. Future reservoir operations should prepare for climate change-related increases in temperature and insignificant changes in precipitation, and adopt adaptive measures, such as rationing water use in various sectors, to mitigate water shortages for supporting sustainable tourism development.

The roles of flood magnitude and duration in controlling channel width and complexity on the Green River in Canyonlands, Utah, USA

Predictions of river channel adjustment to changes in streamflow regime based on relations between mean channel characteristics and mean flood magnitude can be useful to evaluate average channel response. However, because these relations assume equilibrium sediment transport, their applicability to cases where streamflow and sediment transport are decoupled may be limited. These general relations also lack the specificity that is required to connect specific characteristics of the streamflow and sediment regime with the dynamics of channel morphological change that create channel complexity, which is often of ecological interest. We integrate historical records of channel change, observations of scour and fill during a snowmelt flood, measurements of sediment transport, and predictions from a two-dimensional streamflow model to describe how annual peak flow magnitude and peak-flow duration interact with the upstream sediment supply to control channel form for a 15-km study reach on the regulated Green River in Canyonlands National Park, Utah. Two major decadal-scale episodes of channel narrowing have occurred within the study area. For each of these episodes, the reduction in average channel width was consistent with the change predicted by hydraulic geometry relations as a function of average flood magnitude. However, channel narrowing occurred during periods of exceptionally low annual floods. The most recent episode of channel narrowing occurred between 1988 and 2009, during low-flow cycles when the 5-yr mean peak flow was less than 60% of the long-term (1959–2016) mean peak flow. These findings, together with findings from previous studies, demonstrate that decreases in peak-flow magnitude caused by streamflow regulation, climate change, or a combination of those factors have driven episodes of channel narrowing on the Green River. Observations of streamflow, sediment-transport, and morphologic change coupled with predictions from a two-dimensional streamflow model indicate that peak flow magnitudes of at least 75% of the long-term mean peak flow are required to transport bed-material sand in suspension in all regions of the multi-thread channel and that the ~2-month duration of the snowmelt flood played an important role in creating conditions necessary to maintain channel conveyance. These results indicate that detailed characterizations of channel response such as these are needed to predict how river channels will respond to changes in streamflow regime that affect annual peak flow magnitude and duration.

Improving Reservoir Outflow Estimation for Ungauged Basins Using Satellite Observations and a Hydrological Model

AbstractNowadays, most of rivers globally are regulated by dams and reservoirs, which have substantially altered natural streamflow regimes. Understanding the impacts of these dams and reservoirs on streamflow is essential for water resources management. In situ reservoir release data or actual reservoir operating rules are difficult to obtain, particularly for transboundary rivers, resulting in the tremendous difficulty of simulating exact reservoir behaviors. This study aims to use easy‐to‐obtain satellite observations combined with a distributed hydrological model to estimate reservoir releases at the daily time scale. The developed Satellite‐Based Reservoir routing Scheme (SBRS) was applied to two individual reservoirs in the United States and Thailand and cascade reservoirs on the Lancang River in China. The normalized root‐mean‐square error (NRMSE), correlation coefficient (CC), and hydrographs of daily regulated streamflow simulations were used to assess the performance of the reservoir release simulations. The SBRS was compared with four other global reservoir operation schemes and showed better overall performance with higher CC and lower NRMSE. In addition, the SBRS performed better for the individual reservoirs (CC > 0.6, NRMSE < 0.2) than the cascade reservoirs, which is attributed to the uncertainty in the simulation of inflow and reservoir storage changes and to the lack of remote sensing data for all the cascade reservoirs. This study explores the potential of satellite observations combined with hydrological modeling in elucidating reservoir behaviors in ungauged and/or transboundary river basins. A better understanding of reservoir behaviors serves as a basis for water resources management and provides a more cooperative environment for all stakeholders of a basin.

A Brief Analysis of Conceptual Model Structure Uncertainty Using 36 Models and 559 Catchments

AbstractThe choice of hydrological model structure, that is, a model's selection of states and fluxes and the equations used to describe them, strongly controls model performance and realism. This work investigates differences in performance of 36 lumped conceptual model structures calibrated to and evaluated on daily streamflow data in 559 catchments across the United States. Model performance is compared against a benchmark that accounts for the seasonality of flows in each catchment. We find that our model ensemble struggles to beat the benchmark in snow‐dominated catchments. In most other catchments model structure equifinality (i.e., cases where different models achieve similar high efficiency scores) can be very high. We find no relation between the number of model parameters and performance during either calibration or evaluation periods nor evidence of increased risk of overfitting for models with more parameters. Instead, the choice of model parametrization (i.e., which equations are used and how parameters are used within them) dictates the model's strengths and weaknesses. Results suggest that certain model structures are inherently better suited for certain objective functions and thus for certain study purposes. We find no clear relationships between the catchments where any model performs well and descriptors of those catchments' geology, topography, soil, and vegetation characteristics. Instead, model suitability seems to relate strongest to the streamflow regime each catchment generates, and we have formulated several tentative hypotheses that relate commonalities in model structure to similarities in model performance. Modeling results are made publicly available for further investigation.

Impact of climate change on streamflow regime of a large Indian river basin using a novel monthly hybrid bias correction technique and a conceptual modeling framework

The study analyses the impact of climate change on streamflow regime of the Mahanadi River basin (MRB) in projected climate scenarios obtained from CMIP5 models. Projections from a total of 9 Global Climate Models (GCMs) were utilized. Integrated MIKE 11 NAM-HD, a conceptual hydrological model was employed to simulate the streamflow at Hirakud and Mundali gauging sites of upper Mahanadi River basin (UMRB) and middle Mahanadi River basin (MMRB), respectively. Prior to generating the streamflow regimes for the projected scenarios, GCM simulated precipitation and temperature were bias corrected using India Meteorological Department (IMD) observed gridded precipitation and temperature datasets. Precipitation was corrected using quantile mapping technique employing four different approaches, i.e., seasonal, hybrid, monthly non-hybrid, and monthly hybrid approaches. Hybrid approaches explicitly correct the extreme rainfall using Generalized Extreme Value (GEV) distribution whereas Gamma distribution is used for normal rainfall. Temperature data was corrected using Gaussian distribution on daily basis employing monthwise time series. L-moments based frequency analysis method was used to estimate the 50-year return period rainfall for observed and bias corrected projected time series to assess the efficacy of bias correction methods in correcting the extreme events. Monthly hybrid approach was found to resolve rainfall climatology over both UMRB and MMRB with improved skill in extreme rainfall correction. Though, monthly non-hybrid approach produced the seasonal cycle of rainfall with highest accuracy, it performed poorly in correcting the extremes. Under projected climate scenarios mean annual rainfall is found to be increasing for BCC-CSM1.1(m), HadGEM2-AO, GFDL-CM3, and IPSL-CM5A-LR whereas other GCMs show mixed signal compared to their mean state of historic period (1976–2005). Streamflow regime in projected climate was analyzed using ensemble mean of simulated streamflow from identified GCMs. Mean monthly streamflow were overall found to be increasing towards the end of the century i.e., in far-future defined as 2070–2099. Daily high flows (defined at 5% and 10% exceedance probability) were found to be increasing in their magnitude and frequency in far-future whereas occurrences of low flows (defined at 90% and 95% exceedance probability) were found to be predominantly decreasing under projected climate.

DATA MINING APPLIED FOR DETERMINING STREAM FLOW PERMANENCE

Abstract. Streamflow permanence is an aspect of great legal importance in Brazil, because streams, depending on their flow regime, are protected or not by law. Various methods, from field methods to computational methods, are used to determine the flow regime of streams, however some are too time spending and computational methods usually need gaging information as input. Furthermore, computational methods used to extract drainage networks do not identify the flow regimes of streams, and modelled drainage networks always need to be refined manually, as some authors indicate that up to 55% of modelled drainage length is ephemeral in some cases. This work proposes a semi-automatic computational method to determine the flow regime of first order streams, which uses 11 morphometric attributes of the mini drainage basins of these streams to develop a classification model using decision tree algorithms. WEKA package was used to perform the data mining process, which resulted on the development of a compact 8 node decision tree. Ten-fold stratified cross-validation was used to validate the model, which obtained an accuracy rate of 70%. The drainage network of the study area extracted with the classical approach was refined after the result of the classification was obtained. Quantitative analysis of channel length by Strahler order shows an overall reduction of 25% in channel length after refinement was undertaken, and for 1st order streams, as much as 31% were classified as ephemeral. Modelling the drainage areas of headwater streams represents a new approach to determining stream flow permanence, and inclusion of new attributes in the model may yield better results in future research.

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

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

Future streamflow regime changes in the United States: assessment using functional classification

Abstract. Streamflow regimes are changing and expected to further change under the influence of climate change, with potential impacts on flow variability and the seasonality of extremes. However, not all types of regimes are going to change in the same way. Climate change impact assessments can therefore benefit from identifying classes of catchments with similar streamflow regimes. Traditional catchment classification approaches have focused on specific meteorological and/or streamflow indices, usually neglecting the temporal information stored in the data. The aim of this study is 2-fold: (1) develop a catchment classification scheme that enables incorporation of such temporal information and (2) use the scheme to evaluate changes in future flow regimes. We use the developed classification scheme, which relies on a functional data representation, to cluster a large set of catchments in the conterminous United States (CONUS) according to their mean annual hydrographs. We identify five regime classes that summarize the behavior of catchments in the CONUS: (1) intermittent regime, (2) weak winter regime, (3) strong winter regime, (4) New Year's regime, and (5) melt regime. Our results show that these spatially contiguous classes are not only similar in terms of their regimes, but also their flood and drought behavior as well as their physiographical and meteorological characteristics. We therefore deem the functional regime classes valuable for a number of applications going beyond change assessments, including model validation studies or predictions of streamflow characteristics in ungauged basins. To assess future regime changes, we use simulated discharge time series obtained from the Variable Infiltration Capacity hydrologic model driven with meteorological time series generated by five general circulation models. A comparison of the future regime classes derived from these simulations with current classes shows that robust regime changes are expected only for currently melt-influenced regions in the Rocky Mountains. These changes in mountainous, upstream regions may require adaption of water management strategies to ensure sufficient water supply in dependent downstream regions. Highlights. Functional data clustering enables formation of clusters of catchments with similar hydrological regimes and a similar drought and flood behavior. We identify five streamflow regime clusters: (1) intermittent regime, (2) weak winter regime, (3) strong winter regime, (4) New Year's regime, and (5) melt regime. Future regime changes are most pronounced for currently melt-dominated regimes in the Rocky Mountains. Functional regime clusters have widespread utility for predictions in ungauged basins and hydroclimate analyses.

Multivariate remotely sensed and in-situ data assimilation for enhancing community WRF-Hydro model forecasting

Flood is one of the most catastrophic natural disasters in the United States, particularly in the Southeast states where hurricanes and tropical storms are most prevalent, causing billions of dollars in damage annually and significant losses of life and property. The Weather Research and Forecasting Hydrological model (WRF-Hydro) is a community-based hydrologic model designed to improve the skill of hydrometeorological forecasts, such as river discharge, through simulating hydrologic prognostic (e.g., soil moisture) and diagnostic (e.g., energy fluxes) variables. These quantities are potentially biased or erroneous due to the uncertainties involved in all layers of hydrologic predictions. In this study, we use an ensemble based Data Assimilation (DA) approach to explore the benefit of independently and jointly assimilating remotely sensed SMAP (Soil Moisture Active Passive) soil moisture (at different spatial resolutions) and USGS streamflow observations to improve the accuracy and reliability of WRF-Hydro model predictions while accounting for uncertainties. This study is conducted over a large region near to Houston, Texas where heavy rainfall from hurricane Harvey caused flooding in 2017. Before implementing DA, we first calibrated the WRF-Hydro model parameters using four United States Geological Survey (USGS) stream gauges installed within the watershed. In this step, we identified the most dominant model parameters, which were used later in the development of joint state-parameter DA. The findings of this study showed that the multivariate assimilation of soil moisture and streamflow observations results in improved prediction of streamflow as compared to univariate assimilation configurations and regardless of the watershed's streamflow regime. The results also revealed that, during the normal streamflow condition, assimilation of downscaled SMAP soil moisture at 1 km spatial resolution, would improve the accuracy of streamflow simulation more than the assimilation of coarse resolution products (i.e., the native SMAP at 36 km spatial resolution and its interpolated version at 9 km spatial resolution). However, during the period of hurricane Harvey, the soil moisture observations at different resolutions showed a similar impact on improving the streamflow prediction.

Estimation of a Suitable Range of Discharges for the Development of Instream Flow Recommendations

Hydrological variability is of great importance for water resources management. Regardless of how rivers are individually managed, numerous research studies have concluded that aquatic organisms are highly dependent on flow regime variability. Nevertheless, natural streamflow regimes are being altered due to human-induced pressures and climate change/variability, and sufficient biological information in not incorporated in efforts to minimize these effects. Thus, there is an urgent need to develop sustainable environmental flow management guidelines to manage the risk associated with alterations to the flow regime particularly in areas where flow-ecology relationships have not been well studied. This study focuses on a stream with high natural flow regime variability, typical in Mediterranean countries. The major finding of this work is that the estimated Suitable Range of Discharges (SRD) could better address environmental water requirements, rather than simply allocating single value minimum ecological flows. SRD was estimated using advocate statistical analysis of hydrological data series, coupled with habitat suitability models to balance the trade-offs between natural flow variability and human water needs. Combination of the aforementioned approaches was made using the West Balkan trout as a biological component which is a very important species for the quantification of environmental flows. Overall implementation of SRD during dry season is likely to provide large habitat areas for 58 to 67% of the time for the small-size fish and 35 to 55% of the time for the large-size West Balkan trout, according to the Weighted Usable Area0.5 threshold index.

Analysis of Discharge Variability in the Naryn River Basin, Kyrgyzstan

Changing climate and land-use practices influencing the natural stream flow processes in the Naryn river basin of Kyrgyzstan. Variations in stream flow regime over 33-years (1980 to 2012) were investigated using daily discharge data of three hydro-stations (Naryn, Ych-Terek and Uzunakmat), located in the Naryn River Basin. Mean monthly discharge (MMD), mean annual discharge (MAD), standard deviation (SD) and coefficient of variation (CV) were calculated to know the spatio-temporal variability. Similarly, Pearson’s correlation coefficient (r) was used to know the relationship between discharge and rainfall. Advanced time-series graph, exceedance probability and frequency distribution were computed using Hydrognomon (V.4.0.3) software to observe the variability and trends in discharge. The results from statistical calculations and software-based computations highlight the monthly, annual, and long term spatio-temporal discharge variability, extreme events, distribution and changes in stream flow records. This study preciously creates the frequency and trends of seasonal discharge, annual discharge cycle, and range of highest and lowest discharge flows. The weak and negative relationship (-0.2121, -0.4238) between rainfall and discharge propose for more investigation of climatic parameters and the topography of Tian Shan Mountain perhaps influencing discharge variability due to melting of glacier at high altitude. The flow regime of the Naryn river basin over the past 33-years perhaps changed due to climatic fluctuations, with the seasonal snowmelt timing (Post-Spring, Summer, Pri-Autumn), precipitations period (March-October), and large-scale land-use alterations.