Streamflow Characteristics and Changes in Kolyma Basin in Siberia

Abstract This study documents major changes in streamflow hydrology over the Kolyma watershed due to climatic variations and human impacts. Streamflow seasonal cycles over the basin are characteristic of the northern region, with the lowest runoff in April and peak flow in June. Analyses of monthly flows and trends show that reservoir construction and operation have considerably affected streamflow regimes. Comparisons of mean monthly discharge records between pre- and post-1986 dam periods indicate that the mid–lower basin (downstream of the dam) experienced significant increase in low flows and decrease in peak flows after dam construction. For example, mean monthly flows during the post-dam period at the Ust’-Srednekan station (located 1423 km downstream of the dam) has strongly increased by about 205 m3 s−1 (or 522%–3157%) during December–April, and decreased by 133 m3 s−1 (41%) in June. Long-term monthly discharge data reveal an overall increase in streamflow during low flow seasons; the increase is greater for the stations located downstream of the dam. The Srednekolunsk station (1720 km from dam) shows low flow increase ranging from 130 (43%) to 268 m3 s−1 (454%) during November–April, and high discharge decrease by 2550 to 519 m3 s−1 during June–August in the post-dam era (1986–2000). These changes in flow patterns are mainly caused by reservoir regulation, as reservoirs release water in winter for power generation and store water in summer for flood control. Dam impact on flow regimes and changes are visible along the main river trunk; thus, the cold season discharge increase at the basin outlet is primarily the result of reservoir regulation. Annual discharge records show different changes within the Kolyma basin, with moderate increases in the upper basin and weak decreases in the mid–lower basin. Overall annual discharge near the basin outlet has decreased by 1.5% during 1978–2000. This study emphasizes the importance of human activities (particularly reservoirs) on seasonal and regional hydrology changes and points to the need to further examine natural causes and human impacts over other high-latitude watersheds.

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Seasonal and inter-annual variations in carbon fluxes in a tropical river system (Tana River, Kenya)

10.5194/bg-2017-31 ◽

2017 ◽

Author(s):

Naomi Geeraert ◽

Fred O. Omengo ◽

Fredrick Tamooh ◽

Trent R. Marwick ◽

Alberto V. Borges ◽

...

Keyword(s):

Human Impacts ◽

Bootstrap Method ◽

River System ◽

Temporal Variations ◽

Discharge Data ◽

Organic C ◽

Annual Variations ◽

Daily Monitoring ◽

Tana River ◽

Annual Discharge

Abstract. Quantification of sediment and carbon (C) fluxes in rivers with strong seasonal and inter-annual variability presents a challenge for global flux estimates as measurement periods are often too short to cover all hydrological conditions. We studied the dynamics of the Tana River (Kenya) from 2012 to 2014 through daily monitoring of sediment concentrations at three sites (Garissa, Tana River Primate Reserve and Garsen) and daily monitoring of C concentrations in Garissa and Garsen during three distinct seasons. In wet seasons, C fluxes were dominated by particulate organic C (POC) and decreased downstream. Dry season fluxes of dissolved inorganic C (DIC) and POC had a similar share in total C flux at both locations while POC fluxes increased downstream. The dissolved organic C (DOC) flux did not show strong spatial nor temporal variations. The construction of constituent rating curves with a bootstrap method in combination with daily discharge data (1942–2014) provided potential sediment and C flux ranges as a function of annual discharge. At low annual discharge, our estimates generally predict a net decrease of sediment and C storage between the upstream and downstream site. As the annual discharge increases, our simulations shift toward net retention. This analysis allowed us to infer how variations in discharge regime, related to climate or human impacts, may affect riverine fluxes. Overall, we estimate that retention was dominant: integration over all simulations resulted in an average net retention of sediment (~2.9 Mt yr−1), POC (~18000 tC yr−1), DOC (~920 tC yr−1) and DIC (~1200 tC yr−1) over the 73 years of discharge measurements.

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Nitrogen patterns in subsurface waters of the Yzeron stream: effect of combined sewer overflows and subsurface–surface water mixing

Water Science & Technology ◽

10.2166/wst.2013.531 ◽

2013 ◽

Vol 68 (12) ◽

pp. 2632-2637 ◽

Cited By ~ 1

Author(s):

A. M. Aucour ◽

T. Bariac ◽

P. Breil ◽

P. Namour ◽

L. Schmitt ◽

...

Keyword(s):

Surface Water ◽

Cold Season ◽

Low Flow ◽

Subsurface Water ◽

Urban Stream ◽

Nitrogen Forms ◽

Combined Sewer Overflows ◽

Combined Sewer ◽

Subsurface Waters ◽

Sewer Overflows

Urbanization subjects streams to increased nitrogen loads. Therefore studying nitrogen forms at the interface between urban stream and groundwater is important for water resource management. In this study we report results on water δ18O and nitrogen forms in subsurface waters of a stream (Yzeron, France). The sites studied were located upstream and downstream of combined sewer overflows (CSO) in a rural area and a periurban area, respectively. Water δ18O allowed us to follow the mixing of subsurface water with surface water. Dissolved organic nitrogen and organic carbon of fine sediment increased by 20–30% between rural and periurban subsurface waters in the cold season, under high flow. The highest nitrate levels were observed in rural subsurface waters in the cold season. The lowest nitrate levels were found in periurban subsurface waters in the warm season, under low flow. They corresponded to slow exchange of subsurface waters with channel water. Thus reduced exchange between surface and subsurface waters and organic-matter-rich input seemed to favor nitrate reduction in the downstream, periurban, subsurface waters impacted by CSO.

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The Application of Box–Cox Transformation to Determine the Standardised Precipitation Index (SPI), the Standardised Discharge Index (SDI) and to Identify Drought Events: Case Study in Eastern Kujawy (Central Poland)

Journal of Water and Land Development ◽

10.2478/jwld-2014-0017 ◽

2014 ◽

Vol 22 (1) ◽

pp. 3-15 ◽

Cited By ~ 4

Author(s):

Arkadiusz Bartczak ◽

Ryszard Glazik ◽

Sebastian Tyszkowski

Keyword(s):

Normal Distribution ◽

Meteorological Data ◽

Precipitation Index ◽

Low Flow ◽

Monthly Precipitation ◽

Discharge Data ◽

Central Poland ◽

Winter Half ◽

Bartlett’S Test ◽

Standardised Precipitation Index

Abstract The article presents the results of research into the transformation of series of hydro-meteorological data for determining dry periods with the Standardised Precipitation Index (SPI) and the Standardised Discharge Index (SDI). Time series from eight precipitation stations and five series of river discharge data in Eastern Kujawy (central Poland) were analysed for 1951–2010. The frequency distribution of the series for their convergence with the normal distribution was tested with the Shapiro–Wilk test and homogeneity with the Bartlett's test. The transformation of the series was done with the Box–Cox technique, which made it possible to homogenise the series in terms of variance. In Poland, the technique has never been used to determine the SPI. After the transformation the distributions of virtually all series complied with the normal distribution and were homogeneous. Moreover, a statistically significant correlation between the δ transformation parameter and the skewness of the series of monthly precipitation was observed. It was similar for the series of mean monthly discharges in the winter half-year and the hydrological year. The analysis indicates an alternate occurrence of dry and wet periods both in case of precipitation and run-offs. Drought periods coincided with low flow periods. Thus, the fluctuations tend to affect the development of agriculture more than long-term ones.

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Improving TIGGE Precipitation Forecasts Using an SVR Ensemble Approach in the Huaihe River Basin

Advances in Meteorology ◽

10.1155/2018/7809302 ◽

2018 ◽

Vol 2018 ◽

pp. 1-15 ◽

Cited By ~ 4

Author(s):

Chenkai Cai ◽

Jianqun Wang ◽

Zhijia Li

Keyword(s):

River Basin ◽

Lead Time ◽

Flood Control ◽

Ensemble Methods ◽

New Method ◽

Support Vector ◽

Huaihe River Basin ◽

Huaihe River ◽

Reservoir Regulation ◽

The Huaihe River

Recently, the use of the numerical rainfall forecast has become a common approach to improve the lead time of streamflow forecasts for flood control and reservoir regulation. The control forecasts of five operational global prediction systems from different centers were evaluated against the observed data by a series of area-weighted verification and classification metrics during May to September 2015–2017 in six subcatchments of the Xixian Catchment in the Huaihe River Basin. According to the demand of flood control safety, four different ensemble methods were adopted to reduce the forecast errors of the datasets, especially the errors of missing alarm (MA), which may be detrimental to reservoir regulation and flood control. The results indicate that the raw forecast datasets have large missing alarm errors (MEs) and cannot be directly applied to the extension of flood forecasting lead time. Although the ensemble methods can improve the performance of rainfall forecasts, the missing alarm error is still large, leading to a huge hazard in flood control. To improve the lead time of the flood forecast, as well as avert the risk from rainfall prediction, a new ensemble method was proposed on the basis of support vector regression (SVR). Compared to the other methods, the new method has a better ability in reducing the ME of the forecasts. More specifically, with the use of the new method, the lead time of flood forecasts can be prolonged to at least 3 d without great risk in flood control, which corresponds to the aim of flood prevention and disaster reduction.

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Estimating the hydrodynamic and morphodynamic characteristics using Entropy theory at the confluence of Negro and Solimões Rivers

10.5194/egusphere-egu21-10330 ◽

2021 ◽

Author(s):

Farhad Bahmanpouri ◽

Silvia Barbetta ◽

Carlo Gualtieri ◽

Marco Ianniruberto ◽

Naziano Filizola ◽

...

Keyword(s):

Velocity Distribution ◽

Flow Characteristics ◽

Low Flow ◽

Entropy Theory ◽

Velocity Data ◽

Flow Conditions ◽

Mean Velocity ◽

Discharge Data ◽

Confluence Zone ◽

Error Percentage

When two mega rivers merge the mixing of two flows results in a highly complex three-dimensional flow structure in an area known as the confluence hydrodynamic zone. In the confluence zone, substantial changes occur to the hydrodynamic and morphodynamic features which are of significant interest for researchers. The con&#64258;uence of the Negro and Solim&#245;es Rivers, as one of the largest river junctions on Earth, is the study area of the present research. During the EU-funded Project &#8220;Clim-Amazon&#8221; (2011-2015), velocity data were collected using an ADCP vessel operating under high and low flow conditions in different locations at that confluence (Gualtieri et al., 2019). By applying the Entropy theory developed by Chiu (1988) for natural channels and simplified by Moramarco et al. (2014), the two-dimensional velocity distribution, as well as depth-averaged velocity, were calculated at the different transects along the confluence zone, using only the surface velocities observation. The estimated data yielded 6.6% and 6.9% error percentage for the discharge data related to high and low flow conditions, respectively, and 8.4% and 8.3% error percentage for the velocity data related to high and low flow conditions, respectively. Regardless of the flow condition, these preliminary results also suggest the potential points at the confluence zone for the maximum local scouring. The findings of the current research highlighted the potential of Entropy theory to estimate the flow characteristics at the large river&#8217;s confluence, just starting from the measure of surface velocities. This is of considerable interest for monitoring high flows using&#160;no-contact technology, when ADCP or other contact equipment cannot be used for the safety of operators and risks for equipment loss.&#160;Keywords: Amazon River, Negro/Solim&#245;es Confluence, Entropy Theory, Velocity Distribution, Local ScouringReferencesGualtieri, C., Ianniruberto, M., Filizola, N. (2019). On the mixing of rivers with a difference in density: the case of the Negro/Solim&#245;es confluence, Brazil. Journal of Hydrology, 578(11), November 2019, 124029,Chiu, C. L. (1988). &#8220;Entropy and 2-D velocity distribution in open channels&#8221;. Journal of Hydrologic Engineering, ASCE, 114(7), 738-756Moramarco, T., Saltalippi, C., Singh, V.P. (2004). &#8220;Estimation of mean velocity in natural channels based on Chiu&#8217;s velocity distribution equation&#8221;. Journal of Hydrologic Engineering, ASCE, 9 (1), pp. 42-50

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Environmental flow envelopes: quantifying ecosystem-threatening flow alterations

10.5194/egusphere-egu21-14627 ◽

2021 ◽

Author(s):

Vili Virkki ◽

Elina Alanärä ◽

Miina Porkka ◽

Lauri Ahopelto ◽

Tom Gleeson ◽

...

Keyword(s):

Lower Bound ◽

Upper Bound ◽

Human Impacts ◽

Well Being ◽

Environmental Flow ◽

Freshwater Ecosystems ◽

Low Flow ◽

Anthropogenic Pressure ◽

Basin Scale ◽

Climate Forcings

The benefits of harnessing rivers into human use should not come with a disproportionate expense on the Earth system. Especially, freshwater ecosystems suffer greatly from direct and indirect human impacts, such as excessive water withdrawals and climate change, which are expected to only increase in the near future. Here, we aim for quantifying the extent and degree of considerable flow alterations that threaten the well-being of freshwater ecosystems, across the world.At the global scale, the ecological status of river systems is often assessed using global hydrological models (GHMs) and hydrological environmental flow (EF) methods. These suffer from substantial uncertainties: 1) the GHMs parameterised with variable climate forcings may give highly dispersed discharge estimates and 2) individual hydrological EF methods capture ecosystem water needs poorly. We tackle these sources of uncertainty by introducing a novel methodology: environmental flow envelopes (EFEs). The EFE is an envelope of safe discharge variability between a lower and an upper bound, defined at the sub-basin scale in monthly time resolution. It is based on pre-industrial (1801-1860) discharge and a large ensemble of EF methods, GHMs, and climate forcings, using ISI-MIP2b data. Using the EFE, we can simultaneously assess the frequency and severity of ecosystem-threatening flow alterations.Comparing post-industrial (1976-2005) discharge to the EFEs, discharge in 32.7% of the total 3860 sub-basins, covering 28.4% of the global landmass, violates the EFE during more than 10% of all months across four GHMs. These violations are considered as severe threats to freshwater ecosystems. The most impacted regions include areas with high anthropogenic pressure, such as the Middle East, India, Eastern Asia, and Middle America. The violations clearly concentrate on the EFE lower bound during low or intermediate flow seasons. Discharge in 61.4% of sub-basins violates the EFE during more than 10% of low flow season months, average violation being 47.5% below the safe limit denoted by EFE lower bound. Indications of significantly increased flows by violations of the EFE upper bound are fewer and further apart, as well as lower bound violations during high flow season.Although fractional discharge allocations alone cannot fully capture the ecosystem water needs, this study is a step towards less uncertainty in global EF assessments. The introduced method provides a novel, globally robust way of estimating ecosystem water needs at the sub-basin scale. The results of this study underline the importance of the low flow season, during which EFE violations are the most prevalent. While only preliminary evidence of significantly increased flows emerges in relatively few areas, the EFE upper bound would benefit from further research. The EFE methodology can be used for exploring macro-regional areas where anthropogenic flow alteration threatens freshwater ecosystems the most. However, case-specific studies incorporating factors beyond quantitative flow only are required for practical implications.

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Global BROOK90: validation, uncertainties, current progress and future outline.

10.5194/egusphere-egu21-742 ◽

2021 ◽

Author(s):

Ivan Vorobevskii ◽

Rico Kronenberg

Keyword(s):

Water Balance ◽

Model Performance ◽

Low Flow ◽

Easy Access ◽

Climate Projections ◽

Seasonal Forecasts ◽

Water Balance Components ◽

Discharge Data ◽

Small Catchment ◽

Wide Range

&#8216;Just drop a catchment and receive reasonable model output&#8217; &#8211; still stays as motto and main idea of the &#8216;Global BROOK90&#8217; project. The open-source R-package is build-up on global land cover, soil, topographical, meteorological datasets and the lumped hydrological model as a core to simulate water balance components on HRU scale all over the world in an automatic mode. First introduced in EGU2020 and followed by GitHub code release including an publication of methodology with few examples we want to continue with the insights on the current state and highlight the future steps of the project.A global validation of discharge and evapotranspiration components of the model showed promising results. We used 190 small (median size of 64 km2) catchments and FLUXNET data which represent a wide range of relief, vegetation and soil types within various climate zones. The model performance was evaluated with NSE, KGE, KGESS and MAE. In more than 75 % of the cases the framework performed better than the mean of the observed discharge. On a temporal scale the performance is significantly better on a monthly vs daily scale. Cluster analysis revealed that some of the site characteristics have a significant influence on the performance. Additionally, it was found that Global BROOK90 outperforms GloFAS ERA5 discharge reanalysis (for the category with smallest catchments).A cross-combination of three different BROOK90 setups and three forcing datasets was set up to reveal uncertainties of the Global BROOK90 package using a small catchment in Germany as a case study. Going from local to regional and finally global scale we compared mixtures of model parameterization schemes (original calibrated BROOK90, EXTRUSO and Global BROOK90) and meteorological datasets (local gauges, RaKlida and ERA5). Besides high model performances for a local dataset plus a calibrated model and weaker results for ERA5 and the Global BROOK90, it was found that the ERA5 dataset is still able to provide good results when combined with a regional and local parameterization. On the other side, the combination of a global parameterization with local and regional forcings gives still adequate, but much worse results. Furthermore, a hydrograph separation revealed that the Global BROOK90 parameterization as well as ERA5 discharge data perform weaker especially within low flow periods.Currently, some new features are added to the original package. First, with the recent release of the ERA5 extension, historical simulations with the package now are expanded to 1950-2021 period. Additionally, an alternative climate reanalysis dataset is included in the framework (Merra-2, 0.5x0.625-degree spatial resolution, starting from 1980). A preliminary validation shows insignificant differences between both meteorological datasets with respect to the discharge based model performance.Further upgrades of the framework will include the following core milestones: recognition of forecast and climate projections and parameter optimization features. In the nearest future we plan to utilize full power of the Climate Data Store for easy access to seasonal forecasts (i.e. ECMWF, DWD, NCEP) as well as climate projections (CMIP5) to extend the package&#8217;s scope to predict near and far future water balance components.

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Comparison of field measurements to predicted reaeration coefficients, k2, in the application of a water quality model, QUAL2E, to a tropical river

Water Science & Technology ◽

10.2166/wst.2002.0202 ◽

2002 ◽

Vol 46 (9) ◽

pp. 47-54 ◽

Cited By ~ 6

Author(s):

M. Mohamed ◽

J.D. Stednick ◽

F.M. Smith

Keyword(s):

Water Quality ◽

Standard Error ◽

Field Measurements ◽

Water Quality Modeling ◽

Low Flow ◽

Quality Model ◽

Predictive Equations ◽

Discharge Data ◽

Study Results ◽

Reaeration Coefficient

Some of the many tools used for watershed management are mathematical and computer models for wasteload allocations. QUAL2E is one of the most popular water quality models used for such purposes. The question arises as to whether the model is applicable in a different climate such as that in the tropics. In this study, QUAL2E was used to model Sg. Selangor River in Malaysia using the predictive equations for reaeration coefficient (k2) within the model and the measured reaeration coefficients for the river. The study results indicated that use of the reaeration coefficient (k2) measured at Sg. Selangor River did give the lowest standard error (SE) for the simulation of water quality during the 7Q10 low-flow period which is considered as the worst scene scenario in water quality modeling. But during calibration and validation using actual low-flow discharge data, the measured reaeration coefficients did not give the lowest standard error (SE). In conclusion, the results indicated that QUAL2E is applicable in tropical rivers when used with the modeled river parameters (i.e. hydraulic parameters, meteorological conditions etc.). Measured reaeration coefficients produced good results and several predictive equations also produced comparatively good results.

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Analyses of Monthly Discharges in Slovakia Using Hydrological Exploratory Methods

Proceedings ◽

10.3390/ecws-3-05824 ◽

2018 ◽

Vol 7 (1) ◽

pp. 18

Author(s):

Mária Ďurigová ◽

Dominika Ballová ◽

Kamila Hlavčová

Keyword(s):

Change Points ◽

Hydrological Data ◽

Pettitt Test ◽

The Mean ◽

Monthly Discharge ◽

Meteorological Elements ◽

The Relationship ◽

Annual Discharge ◽

Hydrological Regimes

Detailed analyses of hydrological data are necessary in order to prove changes in their character. This article focuses on an analysis of the average monthly discharges of 14 stage-discharge gauging stations in Slovakia. The measured period is from 1931 to 2016. The approaches used are hydrological exploration methods, which were created by hydrologists to describe the behavior of hydrological time series. The methods are used to identify a change-point using an analysis of any residuals, the Pettitt test, and an analysis of the relationship between the mean annual discharge deviations from the long-term annual discharge and the deviations of the average monthly discharge from the long-term average monthly discharge. A considerable number of change-points were identified in the 1970s and 1980s. The results of the analyses show changes in the hydrological regimes, but to confirm the accuracy of the outcomes, it is also necessary to examine other hydrological and meteorological elements such as, e.g., precipitation and the air temperature.

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Changes in Latvian river discharge regime at the turn of the century

Hydrology Research ◽

10.2166/nh.2012.007 ◽

2012 ◽

Vol 44 (3) ◽

pp. 554-569 ◽

Cited By ~ 8

Author(s):

Elga Apsīte ◽

Ilze Rudlapa ◽

Inese Latkovska ◽

Didzis Elferts

Keyword(s):

River Runoff ◽

River Discharge ◽

Large Scale ◽

Hydrological Regime ◽

Turn Of The Century ◽

Significant Trend ◽

Low Flow ◽

Data Series ◽

Discharge Data ◽

Baltic Countries

The study deals with turn-of-the-century changes in the total annual river runoff distribution and high and low flows in Latvia, covering river basins within four hydrological districts which vary according to size and physiographical conditions. Mathematical statistical methods were applied in the analysis of river discharge data series for two study periods of 1951–2009 and 1881–2009. The present results confirm the basic statement concerning the Baltic countries that major significant changes in river runoff during the last two decades have occurred between spring (decrease) and winter (increase) seasons. Mostly insignificant changes in summer runoff and significant/insignificant changes in autumn runoff were found. Analysis shows that a statistically significant trend of increase in low flow for the cold period and a significant trend of decrease in the high discharge and coefficient d of uneven runoff distribution were detected. Changes in river hydrological regime are mainly caused by changes in large-scale atmospheric circulation processes following climate warming, which has taken place. Latvian river hydrography has therefore changed and become more similar to Western European rivers.

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