Source Of Streamflow Research Articles

Estimating the sources of stream water in snow dominated catchments of western Himalayas

Snow and glaciers are important freshwater resources in the Himalayan catchments for all biological activities. However, under recent climate change, these resources are decreasing, thereby posing a serious threat to the future freshwater resources among the Himalayan catchments. Therefore, understanding the hydrological behaviour and sources of streamflow is necessary for better assessment, planning and management of these waters in the mountainous catchments. This study is based on the use of δ18O and d-excess to identify and estimate the different sources of streamflow in the western Himalayas. The isotopic composition of different source waters varied over space and time. These variabilities are attributed to the seasonal meteorological changes, precipitation form, differential melting of snowpacks and moistures sources. The vertical isotope gradients were observed between the sampling sites and the elevation of the basin. The results suggest that snow and snowpack dominantly (up to 55%) contribute to the streamflow during high flow period, while as groundwater maintains the flow in the streams during lean period and contributes up to 78%. The study provides the important insights about the understanding of spatio-temporal variability of different source waters contributing to runoff. In addition, the changing climate could have serious impact on the water resources of the region and thereby affecting the economic and social values of the downstream populations.

Do mixing models with different input requirement yield similar streamflow source contributions? Case study: A tropical montane catchment

AbstractHydrogeochemical based mixing models have been successfully used to investigate the composition and source identification of streamflow. The applicability of these models is limited due to the high costs associated with data collection and the hydrogeochemical analysis of water samples. Fortunately, a variety of mixing models exist, requiting different amount of data as input, and in data scarce regions it is likely that preference will be given to models with the lowest requirement of input data. An unanswered question is if models with high or low input requirement are equally accurate. To this end, the performance of two mixing models with different input requirement, the mixing model analysis (MMA) and the end‐member mixing analysis (EMMA), were verified on a tropical montane headwater catchment (21.7 km2) in the Ecuadorian Andes. Nineteen hydrogeochemical tracers were measured on water samples collected weekly during 3 years in streamflow and eight potential water sources or end‐members (precipitation, lake water, soil water from different horizons and springs). Results based on 6 conservative tracers, revealed that EMMA (using all tracers) and MMA (using pair‐combinations out of the 6 conservative ones), identified the same end‐members: rainfall, soil water and spring water., as well as, similar contribution fractions to streamflow from rainfall 21.9% and 21.4%, soil water 52.7% and 52.3%, and spring water 26.1% and 28.7%, respectively. Our findings show that a hydrogeochemical mixing model requiring a few tracers can provide similar outcomes than models demanding more tracers as input data. This underlines the value of a preliminary detailed hydrogeochemical characterization as basis to derive the most cost‐efficient monitoring strategy.

Impact of Coastal Wetland Restoration Plan on the Water Balance Components of Heeia Watershed, Hawaii

Optimal restoration and management of coastal wetland are contingent on reliable assessment of hydrological processes. In this study, we used the Soil and Water Assessment Tool (SWAT) model to assess the impacts of a proposed coastal wetland restoration plan on the water balance components of the Heeia watershed (Hawaii). There is a need to optimize between water needs for taro cultivation and accompanying cultural practices, wetland ecosystem services, and streamflow that feeds downstream coastal fishponds and reefs of the Heeia watershed. For this, we completed two land use change scenarios (conversion of an existing California grassland to a proposed taro field and mangroves to a pond in the wetland area) with several irrigation water diversion scenarios at different percent of minimum streamflow values in the reach. The irrigation water diversion scenarios aimed at achieving sustainable growth of the taro crop without compromising streamflow value, which plays a vital role in the health of a downstream fishpond and coastal environment of the watershed. Findings generally suggest that the conversion of a California grassland to a patched taro field is expected to decrease the baseflow value, which was a major source of streamflow for the study area, due to soil layer compaction, and thus decrease in groundwater recharge from the taro field. However, various taro irrigation water application and management scenarios suggested that diverting 50% of the minimum streamflow value for taro field would provide sustainable growth of taro crop without compromising streamflow value and environmental health of the coastal wetland and downstream fishponds.

Summer precipitation characteristics on the southern Tibetan plateau

AbstractPrecipitation is an important source of streamflow and a critical parameter in hydrological studies. However, spatiotemporal variation of precipitation in the Tibetan Plateau (TP) has been poorly characterized due to the limited distribution of meteorological stations mostly in the lowlands. In this study, we set‐up rain gauges to study summer precipitation on mountain slopes in three catchments of the southern TP from 2013 to 2016. We studied the precipitation gradients (PGs) averaged during the Indian monsoon season (PGms), as well as daily PGs (PGd) and unit PGs (PGu) under various precipitation intensity grades (PIGs) and subdiurnal precipitation distributions. We also analysed the correlations between the PGs and precipitation amounts under various PIGs. Results showed that the mean PGms, PGd and PGu in the study catchments were 0.0071–0.0082% for monsoon season, 0.11–0.13 mm·100 m−1 d−1 and 2.2–3.1%·100 m−1 for the total (nonintensity‐graded) precipitation, but varied widely under different PIGs. PGms, PGd and PGu were all strongly correlated to precipitation amounts, which were relatively consistent between years but varied between different catchments. In addition, the correlations showed a steep positive slope under fine precipitation but became flat or even negative with increasing PIG. Generally, two distinct precipitation peaks were noted in each of the three catchments: a dispersed peak in the morning, and a stronger but sharper peak at around 18:00 LST; overall, this subdiurnal pattern was temporally stable. The mean precipitation durations of the three catchments were approximately 1.0–1.4 hr (nonintensity‐graded) and increased from <0.5 hr, to <1 hr, 2–5 hr and 6–11 hr for trace, light, moderate and heavy precipitation intensities, respectively. Among the various PG units, both PGd and PGu better represented precipitation at different altitudes than that of PGms. Summer precipitation in the study catchments was influenced more by valley‐scale convection than by large‐scale monsoon circulation.

Ensemble Streamflow Forecasting Using an Energy Balance Snowmelt Model Coupled to a Distributed Hydrologic Model with Assimilation of Snow and Streamflow Observations

AbstractIn many river basins across the world, snowmelt is an important source of streamflow. However, detailed snowmelt modeling is hampered by limited input data and uncertainty arising from inadequate model structure and parametrization. Data assimilation that updates model states based on observations, reduces uncertainty and improves streamflow forecasts. In this study, we evaluated the Utah Energy Balance (UEB) snowmelt model coupled to the Sacramento Soil Moisture Accounting (SAC‐SMA) and rutpix7 stream routing models, integrated within the Research Distributed Hydrologic Model (RDHM) framework for streamflow forecasting. We implemented an ensemble Kalman filter for assimilation of snow water equivalent (SWE) observations in UEB and a particle filter for assimilation of streamflow to update the SAC‐SMA and rutpix7 states. Using leave one out validation, it was shown that the modeled SWE at a location where observations were excluded from data assimilation was improved through assimilation of data from other stations, suggesting that assimilation of sparse observations of SWE has the potential to improve the distributed modeling of SWE over watershed grid cells. In addition, the spatially distributed snow data assimilation improved streamflow forecasts and the forecast volume error was reduced. On the other hand, the assimilation of streamflow observations did not provide additional forecast improvement over that achieved by the SWE assimilation for seasonal forecast volume likely due to there being little information content in streamflow at the forecast date prior to its rising during the melt period and this application of particle filter being better suited for shorter timescales.

Hydrochemical Characteristics, Controlling Factors, and Solute Sources of Streamflow and Groundwater in the Hei River Catchment, China

Water scarcity in arid regions is exacerbated by water quality degradation from anthropogenic contamination. In water-scarce regions, it is crucial to identify hydrochemical characteristics and pollution sources for effective water resource management. In this study, the Hei River—located in the Loess Plateau of China, which is an arid region with substantial anthropogenic-induced environmental changes—was selected as the study area to investigate these issues. The major ions of 242 streamflow and groundwater samples were measured during the 2014 and 2015 dry and flood seasons. Using a Piper diagram, a fuzzy membership function, a Gibbs diagram, and a forward model, the hydrochemical facies and water quality of streamflow and groundwater were investigated, and the main river solute sources and relative contributions were determined using quantitative and qualitative methods. The total dissolved solids were 279.6 ± 127.8 mg·L−1 for streamflow and 354.0 ± 157.4 mg·L−1 for groundwater, indicating low salinity water. However, the hydrochemical characteristics varied with season and location. Qualitatively, the atmospheric inputs, human activities, and rock weathering all contributed solutes to the waters but with varying contributions. The following are the mean contributions of analyzed solute source: silicate weathering (45.1 ± 1.1%) > carbonate weathering (34.1 ± 1.6%) > evaporite dissolution (13.7 ± 2.4%) > atmospheric input (5.4 ± 0.1%) > anthropogenic input (1.7 ± 0.1%). In general, water quality was satisfactory, as the majority of samples conformed to drinking water standards. The samples had good water quality because the river solutes were not heavily affected by anthropogenic activities and were primarily controlled by rock weathering. However, localized areas of high anthropogenic impact were identified. Such locations should be prioritized for pollution control and water resource management.

Spatiotemporal Heterogeneity of Water Flowpaths Controls Dissolved Organic Carbon Sourcing in a Snow-Dominated, Headwater Catchment

The non-uniform distribution of water in snowdrift-driven systems can lead to spatial heterogeneity in vegetative communities and soil development, as snowdrifts may locally increase weathering. The focus of this study is to understand the coupled hydrological and biogeochemical dynamics in a heterogeneous, snowdrift-dominated headwater catchment (Reynolds Mountain East, Reynolds Creek Critical Zone Observatory, Idaho, USA). We determine the sources and fluxes of stream water and dissolved organic carbon (DOC) at this site, deducing likely flowpaths from hydrometric and hydrochemical signals of soil water, saprolite water, and groundwater measured through the snowmelt period and summer recession. We then interpret flowpaths using end-member mixing analysis in light of inferred subsurface structure derived from electrical resistivity and seismic velocity transects. Streamwater is sourced primarily from groundwater (averaging 25% of annual streamflow), snowmelt (50%), and water travelling along the saprolite/bedrock boundary (25%). The latter is comprised of the prior year’s soil water, which accumulates DOC in the soil matrix through the summer before flushing to the saprolite during snowmelt. DOC indices suggest that it is sourced from terrestrial carbon, and derives originally from soil organic carbon (SOC) before flushing to the saprolite/bedrock boundary. Multiple subsurface regions in the catchment appear to contribute differentially to streamflow as the season progresses; sources shift from the saprolite/bedrock interface to deeper bedrock aquifers from the snowmelt period into summer. Unlike most studied catchments, lateral flow of soil water during the study year is not a primary source of streamflow. Instead, saprolite and groundwater act as integrators of soil water that flows vertically in this system. Our results do not support the flushing hypothesis as observed in similar systems and instead indicate that temporal variation in connectivity may cause the unexpected dilution behavior displayed by DOC in this catchment.

Tracing surface and ground water with stable isotopes in a small permafrost research catchment

The study aims at assessing groundwater contribution to the streamflow at the small permafrost Shestakovka river watershed in Central Yakutia. Water from stream, lakes, snow, rain, surface flow and suprapermafrost groundwater is characterized by specific isotopic signature. At least one third of the spring flood is formed by “old” pre-event water as showed by mixing model based on stable isotopes as tracers. Presence of talik aquifers associated with sandy hills covered by pine forest suggests that talik groundwater could be an important source of streamflow at the small river basin in continuous permafrost.

Geochemical characterization and modeling of regional groundwater contributing to the Verde River, Arizona between Mormon Pocket and the USGS Clarkdale gage

We use synoptic surveys of stream discharge, stable isotopes, and dissolved noble gases to identify the source of groundwater discharge to the Verde River in central Arizona. The Verde River more than doubles in discharge in Mormon Pocket over a 1.4 km distance that includes three discrete locations of visible spring input to the river and other diffuse groundwater inputs. A detailed study of the Verde River between Mormon Pocket and the USGS Clarkdale Gage was conducted to better constrain the location of groundwater inputs, the geochemical signature and constrain the source of groundwater input. Discharge, water quality parameters (temperature, pH, specific conductance, and dissolved oxygen), stable isotopes (δ18O and δ2H), noble gases (He, Ne, Ar, Kr and Xe), and radon (222Rn) from river water were collected. Groundwater samples from springs and wells in the area were collected and analyzed for tracers measured in the stream along with some additional analytes (major ions, strontium isotopes (87Sr/86Sr), carbon-14, δ13C, and tritium). Groundwater isotopic signature is consistent with a regional groundwater source. Groundwater springs discharging to the river have a depleted stable isotopic signature indicating recharge source up to 1000 m higher than the discharge location in the Verde River and are significantly fresher than stream water. Spring water has a radiocarbon age of several thousand years and some areas have tritium less than the laboratory reporting level or low concentrations of tritium (1.5 TU). The strontium isotopes indicate groundwater interaction with tertiary volcanic rock and Paleozoic sedimentary rocks. Along the study reach with distance downstream, Verde stream water chemistry shows increased 222Rn, freshening, increased 4He, and isotopic depletion with distance downstream. We estimated total groundwater discharge by inverting a stream transport model against 222Rn and discharge measured in the stream. The salinity, 4He, and stable isotope composition of discharging groundwater was then estimated by fitting modeled values to observed in-stream values. Estimated groundwater inflow to the stream was well within the ranges observed in springs, indicating that the main source of streamflow is deep, regional groundwater. These results show that synoptic surveys of environmental tracers in streams can be used to estimate the isotopic composition and constrain the source of groundwater discharging to streams. Our data provide direct field evidence that deep, regional groundwater discharge can be a significant source of streamflow generation in arid, topographically complex watersheds.

Spatio-Temporal Variations of the Stable H-O Isotopes and Characterization of Mixing Processes between the Mainstream and Tributary of the Three Gorges Reservoir

Understanding the runoff characteristics and interaction processes between the mainstream and its tributaries are an essential issue in watershed and water management. In this paper, hydrogen (δD) and oxygen (δ18O) isotope techniques were used in the mainstream and Zhuyi Bay (ZYB) of the Three Gorges Reservoir (TGR) during the wet and dry seasons in 2015. It revealed that (1) Precipitation was the main source of stream flow compared to the TGR water line with meteoric water line of the Yangtse River basin; (2) The δD and δ18O values exhibited a ‘toward lighter-heavier’ trend along mainstream due to the continuous evaporation effect in the runoff direction, and the fluctuations reflected incoming water from the nearest tributaries. The general trend of d-excess increased with increasing distance from the Three Gorges Dam, which indicated that kinetic fractionation was an important process affecting the isotopic composition. The enrichment effect of isotopes was found in the downstream of TGR; (3) Water mass from the TGR mainstream flowed backward to the confluence zone of ZYB via the middle and bottom layers in the dry season, whereas in the wet season, water reversed through the upper-middle layers due to thermal density flows. This study described and demonstrated that the water cycle of TGR was driven by natural environmental variability and operational system, which will provide valuable information for the water resource management and for controlling the algal blooms in the future.

Modification of the SWAT model to simulate regional groundwater flow using a multicell aquifer

AbstractThe soil and water assessment tool (SWAT) has been widely used and thoroughly tested in many places in the world. The application of the SWAT model has pointed out that 2 of the major weaknesses of SWAT are related to the nonspatial reference of the hydrologic response unit concept and to the simplified groundwater concept, which contribute to its low performance in baseflow simulation and its inability to simulate regional groundwater flow. This study modified the groundwater module of SWAT to overcome the above limitations. The modified groundwater module has 2 aquifers. The local aquifer, which is the shallow aquifer in the original SWAT, represents a local groundwater flow system. The regional aquifer, which replaces the deep aquifer of the original SWAT, represents intermediate and regional groundwater flow systems. Groundwater recharge is partitioned into local and regional aquifer recharges. The regional aquifer is represented by a multicell aquifer (MCA) model. The regional aquifer is discretized into cells using the Thiessen polygon method, where centres of the cells are locations of groundwater observation wells. Groundwater flow between cells is modelled using Darcy's law. Return flow from cell to stream is conceptualized using a non‐linear storage–discharge relationship. The SWAT model with the modified aquifer module, the so‐called SWAT‐MCA, was tested in 2 basins (Wipperau and Neetze) with porous aquifers in a lowland area in Lower Saxony, Germany. Results from the Wipperau basin show that the SWAT‐MCA model is able (a) to simulate baseflow in a lowland area (where baseflow is a dominant source of streamflow) better than the original model and (b) to simulate regional groundwater flow, shown by the simulated groundwater levels in cells, quite well.

High levels of endocrine pollutants in US streams during low flow due to insufficient wastewater dilution

Wastewater discharges from publicly owned treatment works are a significant source of endocrine disruptors and other contaminants to the aquatic environment in the US. Although remaining pollutants in wastewater pose environmental risks, treated wastewater is also a primary source of stream flow, which in turn is critical in maintaining many aquatic and riparian wildlife habitats. Here we calculate the dilution factor—the ratio of flow in the stream receiving discharge to the flow of wastewater discharge—for over 14,000 receiving streams in the continental US using streamflow observations and a spatially explicit watershed-scale hydraulic model. We found that wastewater discharges make up more than 50% of in-stream flow for over 900 streams. However, in 1,049 streams that experienced exceptional low-flow conditions, the dilution factors in 635 of those streams fell so low during those conditions that the safety threshold for concentrations of one endocrine disrupting compound was exceeded, and in roughly a third of those streams, the threshold was exceeded for two compounds. We suggest that streams are vulnerable to public wastewater discharge of contaminants under low-flow conditions, at a time when wastewater discharges are likely to be most important for maintaining stream flow for smaller sized river systems. Wastewater can make up a large fraction of stream flow. An analysis of over 14,000 US streams shows that under severe low-flow conditions, wastewater containing endocrine disruptors is poorly diluted, and many streams exceed safety thresholds.

Evaluating topography‐based predictions of shallow lateral groundwater discharge zones for a boreal lake‐stream system

AbstractGroundwater discharge along streams exerts an important influence on biogeochemistry and thermal regimes of aquatic ecosystems. A common approach for predicting locations of shallow lateral groundwater discharge is to use digital elevation models (DEMs) combined with upslope contributing area algorithms. We evaluated a topography‐based prediction of subsurface discharge zones along a 1500 m headwater stream reach using temperature and water isotope tracers. We deployed fiber‐optic distributed temperature sensing instrumentation to monitor stream temperature at 0.25 m intervals along the reach. We also collected samples of stream water for the analysis of its water isotope composition at 50 m intervals on five occasions representing distinct streamflow conditions before, during, and after a major rain event. The combined tracer evaluation showed that topography‐predicted locations of groundwater discharge were generally accurate; however, predicted magnitude of groundwater inflows estimated from upslope contributing area did not always agree with tracer estimates. At the catchment scale, lateral inflows were an important source of streamflow at base flow and peak flow during a major rain event; however, water from a headwater lake was the dominant water source during the event hydrograph recession. Overall, this study highlights potential utility and limitations of predicting locations and contributions of lateral groundwater discharge zones using topography‐based approaches in humid boreal regions.

Investigating spatiotemporal snow cover variability via cloud-free MODIS snow cover product in Central Alborz Region

Snow is a major source of streamflow in Central Alborz Mountains in northern Iran. Hence, understanding the spatial distribution and temporal variation of snow is crucial for proper management of limited water resources in this region. Since the in-situ measurements in the area are not sufficient, we used the Moderate Resolution Imaging Spectroradiometer (MODIS) snow cover products, for which their capabilities in providing a spatially distributed and accurate mapping of snow have been well demonstrated. In this analysis, we considered all the available MODIS acquisitions from both Aqua and Terra satellites for a total of 4873 daily tiles of MOD10A1 and MYD10A1 with 500-meters spatial resolution (version 5), collected during the winter seasons between years 2002 and 2015. The problem of cloud coverage, with serious constraints to the snow mapping in the area, is addressed by developing a sequential cloud removal algorithm, which applies different methods subsequently considering their performance in each month. The results indicate that the proposed algorithm is able to reduce 94% of cloud coverage and preserve the accuracy of cloud-removed area by 93%. In addition, a clear decreasing trend in snow cover is observed in the region. For example, trend analysis (at 10% significance level) shows that 61% of areas between 2000 and 2300m elevation levels experienced a reduction in duration of annual snow cover. Moreover, a general reduction in the duration of snow season is also evident over the entire study area. In spite of short duration (13years) used in this research, outcomes indicate a severe snow cover reduction during recent years.

Sources of streamflow along a headwater catchment elevational gradient

We used End-Member Mixing Analysis (EMMA) to investigate the spatiotemporal variability of source water contributions to streamflow generation from three headwater catchments that span a precipitation and ecosystem type gradient across ∼1500m elevation in the Colorado Front Range, USA. We additionally characterized the magnitude and type (rain versus snow) of precipitation and the resulting hydrologic response of surface and subsurface waters to this precipitation variability. The three catchments were representative of the montane rain-snow transition zone (snow was 39% of total precipitation; σ (standard deviation)=10%), the subalpine zone (69% snow; σ=5%), and the alpine zone (84% snow; σ=10%). All three catchments were identified as three end-member systems with their respective source waters being groundwater, snow precipitation or melt, rain (montane and subalpine only), and subsurface water from talus slopes (alpine only). Mean annual groundwater contributions were greater in forested catchments (28%; σ=6% in the montane, 31%; σ=8% in the subalpine) than in the alpine (19%; σ=5%) catchment. Snow-derived water contributions to streamflow were inversely related to groundwater and increased with elevation from 46% (σ=15%) in the montane zone to 58% (σ=12%) in the subalpine and 61% (σ=7%) in the alpine. Rain was 27% (σ=8%) of discharge in the montane and 11% (σ=4%) in the subalpine, while talus waters made up the final 21% (σ=12%) of streamflow in the alpine. Our results suggest that subsurface source waters (i.e. groundwater and talus water) that are influenced by the timing, magnitude, and type of recharge and by the storage capabilities of the subsurface may be the most sensitive to climate variability at higher elevations. In contrast, the proportion of rain versus snow was the primary control on source water variability at lower elevations.

Spatial and temporal patterns of precipitation and stream flow variations in Tigris-Euphrates river basin

Tigris and Euphrates river basin (TERB) is one of the largest river basins in the Middle East, and the precipitation (in the form of snowfall) is a major source of streamflow. This study investigates the spatial and temporal variability of precipitation and streamflow in TERB to better understand the hydroclimatic variables and how they varied over time. The precipitation shows a decreasing trend with 1980s being wetter and 2000s being drier. A total of 55 and 40% reduction in high flows in Tigris and Euphrates rivers at T20 and E3 was seen in post-reservoir period. A lag time of 3 to 4 and 5 to 6months was estimated between peak snowfall and runoff time periods. Decreasing precipitation and streamflow along with several planned dams could hamper the sustainability of several Mesopotamian marshlands that completely depend on the water from the Tigris and Euphrates rivers.

StreamFlow 1.0: an extension to the spatially distributed snow model Alpine3D for hydrological modelling and deterministic stream temperature prediction

Abstract. Climate change is expected to strongly impact the hydrological and thermal regimes of Alpine rivers within the coming decades. In this context, the development of hydrological models accounting for the specific dynamics of Alpine catchments appears as one of the promising approaches to reduce our uncertainty of future mountain hydrology. This paper describes the improvements brought to StreamFlow, an existing model for hydrological and stream temperature prediction built as an external extension to the physically based snow model Alpine3D. StreamFlow's source code has been entirely written anew, taking advantage of object-oriented programming to significantly improve its structure and ease the implementation of future developments. The source code is now publicly available online, along with a complete documentation. A special emphasis has been put on modularity during the re-implementation of StreamFlow, so that many model aspects can be represented using different alternatives. For example, several options are now available to model the advection of water within the stream. This allows for an easy and fast comparison between different approaches and helps in defining more reliable uncertainty estimates of the model forecasts. In particular, a case study in a Swiss Alpine catchment reveals that the stream temperature predictions are particularly sensitive to the approach used to model the temperature of subsurface flow, a fact which has been poorly reported in the literature to date. Based on the case study, StreamFlow is shown to reproduce hourly mean discharge with a Nash–Sutcliffe efficiency (NSE) of 0.82 and hourly mean temperature with a NSE of 0.78.

Assessment of a lumped coupled flow‐isotope model in data scarce Boreal catchments

AbstractQuantifying streamflow sources within remote, data scarce, Boreal catchments remains a significant challenge because of limited accessibility and complex, flat topography. The coupled use of hydrometric and isotopic data has previously been shown to facilitate quantification of streamflow sources, but application has generally been limited to small basins and short time scales. A lumped flow‐isotope model was used to estimate contributing streamflow sources (soil, ground, and wetland water) over a four‐year period in two large nested headwater catchments (Sapochi and Odei Rivers) in northern Manitoba, Canada. On average, the primary streamflow source was estimated as soil water (60%) in the Sapochi River, and groundwater (54%) in the Odei River. A strong seasonal influence was observed: soil water was the primary streamflow source in summer, changing to groundwater and wetlands during the winter. Interannual variability in streamflow sources was strongly linked to the presence or absence of late summer rainfall. The greatest uncertainties in source quantification were identified during the spring freshets and high precipitation events, and hence, simulations may be improved through explicit representation of the soil freeze/thaw process and data collection during this period. Assessment of primary streamflow components and qualitative uncertainty estimation using coupled isotope‐flow modelling is an effective method for first‐order identification of streamflow sources in data sparse remote headwaters. Copyright © 2016 John Wiley & Sons, Ltd.

Isotopic time series partitioning of streamflow components under regional climate change in the Urumqi River, northwest China

ABSTRACTWe investigated the isotopic composition of the Urumqi River and documented seasonal variability attributable to the mixing of various flow sources. Next, we applied these isotopic signals to partition the sources and studied their temporal variability in summer. The isotope hydrology separation results indicated that groundwater is the dominant streamflow source (approximately 62.7%) in the Urumqi River. Precipitation is an important source for the Urumqi River; approximately 19.1–20.7% of the runoff came from precipitation during summer and early autumn. In summer, approximately 21.1% of the runoff is derived from glacial meltwater. In summer, with the increasing distance to the glacier front, groundwater accounts for a larger and larger percentage of the river water, and the contributions of precipitation and glacial meltwater gradually diminish. Throughout 2012, the proportions of precipitation and glacial meltwater in the streamflow were 17.6% and 14.7%, respectively, and only 5% of the streamflow was derived from snowmelt.Editor Z. W. Kundzewicz; Associate editor not assigned

The ‘teflon basin’ myth: hydrology and hydrochemistry of a seasonally snow-covered catchment

Background: Snow and ice melt provide sensitive indicators of climate change and serve as the primary source of stream flow in alpine basins.Aims: We synthesise the results of hydrological and hydrochemical studies during the period 1995–2014, building on a long history of earlier work focused on snow and water on Niwot Ridge and the adjacent Green Lakes Valley (GLV), which is part of the Niwot Ridge Long Term Ecological Research site (NWT LTER).Methods: These studies are discussed in the context of how snow, snowmelt and runoff reflect changing local climate. We review recent results of snow, snowmelt, hydrology and hydrochemistry from the plot to the basin scale, utilising new tools such as continuous global positioning system (GPS) measurements of snow depth, along with remotely-sensed measurements of snow-covered area and melt, combined with long-term measurements of snow properties, discharge and solute and isotopic content of water.Results and Conclusions: Surface–groundwater interactions are important components of water quantity and quality in alpine basins. Some or most snowmelt infiltrates underlying soils and bedrock, transporting soil and bedrock products to surface waters. Infiltrating snowmelt, along with increased melt of stored ice, increases the hydrologic connectivity between the terrestrial and aquatic systems. Alpine basins are being impacted by increases in atmospheric nitrogen deposition, which has caused changes in soil microbial processes such as nitrification. Nitrate, dissolved organic carbon and dissolved organic nitrogen are thus flushed from soils and talus to streams. Our long-term results show that alpine catchments, such as Green Lake 4 at NWT LTER+, have the greatest sensitivity and least resilience to climate warming, with any warming leading to increased water yields.