Winter River Flow Research Articles

Trends in the Minimum Winter River Flow on the Territory of the Basin of Lake Sevan

Trends in the Minimum Winter River Flow on the Territory of the Basin of Lake Sevan

Effects of Winter Warming on Alpine Permafrost Streamflow in Xinjiang China and Teleconnections with the Siberian High

The climatic warming-induced shrinking of permafrost currently encompasses 65% of alpine areas in North China, where a large population relies on its water and land resources. With increasing recognition of the economic and ecological impacts of permafrost basins, forecasts of environmental vulnerability have gained prominence. However, the links between permafrost and winter water resources remain inadequately explored, with most studies focusing on in-situ measurements related to snow cover and frozen layer thickness. Evaluating more complex phenomena, such as the magnitude and persistence of air temperature or low streamflow, depends on numerous climate-driven factors interacting through various subsurface flow mechanisms, basin drainage mechanics, and hydro-climatic correlations at a macroscale. The present study focuses on winter warming, flow increases, and their teleconnections in Xinjiang, China. The research analyzes their links to the atmospheric cycle of the Siberian High (SH) using long-term data spanning 55 years from two large alpine permafrost basins. Changes in variability and correlation persistence were explored for the past decades, and significant variability and connections were constructed using statistical correlation. The years 1980 and 1990 were a turning point when both winter temperatures and winter river flow began to exhibit a notable and consistent upward trend. Subsequently, the period from the mid-1990s to 2013 was characterized by high variability and persistence in these trends. The influence of the SH plays a dominant role in regard to both winter temperatures and river flow, and these variabilities and correlations can be utilized to estimate and predict winter flow in ungauged permafrost rivers in Xinjiang China.

ОЦЕНКА ОБЪЕМОВ НАЛЕДЕЙ В БАССЕЙНЕ РЕКИ ИНДИГИРКА

On the basis of corrected Landsat data for 2013-2017, a modern assessment of aufeis in the Indigirka River basin and its partial catchments with an area of 1830 to 305 000 km2 was conducted. The potential contribution of the aufeis flow to the formation of the water balance of rivers during various phases of hydrological regime was calculated. During the phase of the maximum development, the aufeis area of partial catchments ranges from 0.30 to 1.49%, reaching 0.54% of the total area of the Indigirka River basin. The aufeis resources (water content in aufeis) of the Indigirka River basin are 10.0 mm of the runoff level or in total 3.5 km3 . For individual rivers, the aufeis flow can reach 5-28 mm per year, which makes up 2.6 to 20.8% (an average is 8.1%) of river runoff. On average, water resources stored in aufeis make up 235% of the winter river flow (135% for the Indigirka River basin). The contribution of the aufeis flow during the spring flood can reach 39% and is 13.7% in the outlet of the Indigirka River basin. The ambiguous impact of climate change on aufeis (reducing their area and increasing their number) requires further detailed studies.

Climate Control of Multidecadal Variability in River Discharge and Precipitation in Western Europe

The influence of large-scale climate variability on winter river discharge and precipitation across western Europe is investigated. We analyze 60 years of monthly precipitation and river flow data from 18 major western-European rivers and its relationship with dominant teleconnection patterns and climate indices in this region. Results show that winter river flow is characterized by large interannual variability, best correlates with (a) the North Atlantic Oscillation (NAO) at the far-northern (R up to 0.56) and southern latitudes (R up to −0.72), and (b) the West Europe Pressure Anomaly (WEPA) at the middle and northern latitudes, from 42° N to 55° N (R up to 0.83). These indices also explain the interannual variability in autumn and spring discharge in rivers characterized by secondary floods. Compared to the other leading modes of atmospheric variability, WEPA increases the correlations with winter precipitation up to 0.8 in many regions of western and central Europe. A positive WEPA corresponds to a southward shift and an intensification of the Icelandic-Low/Azores-High dipole, driving enhanced precipitation and river discharge in these regions. The correlations with precipitation are slightly higher than those with river discharge, particularly in France, with clear latitudinal gradient. This trend suggests that water storage variability and other catchment characteristics may also influence the interannual variability of river discharge. Seasonal forecasting of the WEPA and NAO winter indices can become a powerful tool in anticipating hydrological risks in this region.

RELATION OF EXTREMES OF MINIMUM WINTER RIVER FLOW WITH TEMPERATURE AND ICE FACTORS

Studies performed in different river basins in the North-West of Russia have shown that a combination of temperature and ice conditions plays a significant role in changing the winter water content of rivers. Air temperature and ice thickness are integral indicators of changes in thermal conditions in the river basin and in the river, regulating through cryogenic processes the supply of groundwater and its discharge into rivers in winter. Therefore, the main predictors used in the work are air temperature, ice thickness, and winter river flow. To obtain quantitative estimates, a comparative analysis of changes in river flow by the end of winter under different temperature and ice conditions was performed. The series of winter runoff of rivers in the basins of the Lovat, Syas, Northern Dvina and Onega rivers with the total period of observations of the runoff and the thickness of the river ice are analyzed –1955-2016 years, temperature – 1936-2016 years. Based on the analysis of a series of observations of river flow, ice thickness, and air temperature lasting more than 50 years, it is concluded that the lowest values of the minimum winter flow of rivers were observed in cold winters, and the highest values were observed in milder winter seasons. With comparable pre-winter water content of rivers in a series of mild non-thawing winters, river flow in the studied basins decreased less intensively and the minimum winter flow was higher on average by 10-20%, and in some cases more.

Brownification and its consequences for the ecosystems of Lake Onego and Vygozerskoe reservoir under influence of climatic and anthropogenic factors

The consequences of climatic changes in the conditions of anthropogenic load weakening are considered for the ecosystems of the largest lake-reservoirs in the northwestern region of Russia (Lake Onego and Vygozerskoe reservoir). The catchment areas of these water bodies are rich in bogs. The rise of the humic substances flow became a new regulatory factor in the functioning of these reservoirs due to an increase in winter river flow in conditions of climate warming. Geochemical indicators of the increasing influence of the catchment area on the water chemical composition in the studied lakes were a simultaneous increase in the color of water (brownification), the concentration of iron and carbon dioxide, and a decrease in pH. The accumulation of iron at the bottom of Lake Onego caused inhibition of deep-water benthic communities. The state of benthos of Vygozerskoe reservoir is associated with the consequences of influence of pulp and paper mill wastewater, the highest toxicity of which was observed in the previous period.

Rainfall and river flow trends for the Western Cape Province, South Africa

Climate change has the potential to alter the spatio-temporal distribution of rainfall, subsequently affecting the supply and demand of water resources. In a water-stressed country such as South Africa, this effect has significant consequences. To this end, we investigated annual and winter rainfall and river flow trends for the Western Cape Province over two periods: 1987–2017 and 1960–2017. Annual rainfall for the most recent 30-year period shows decreasing trends, with the largest magnitude of decrease at the SA Astronomical Observatory rainfall station (-54.38 mm/decade). With the exception of the significant decreasing winter rainfall trend at Langewens (-34.88 mm/decade), the trends vary between stations for the period 1960–2017. For the period 1987–2017, statistically significant decreasing winter trends were found at four of the seven stations, and range from -6.8 mm/decade at Cape Columbine to -34.88 mm/decade at Langewens. Similarly, the magnitudes of decreasing winter river flow at Bree@Ceres and Berg@Franschoek are greater for the more recent 30-year period than for 1960–2017. Correlation coefficients for Vilij@Voeliv rainfall and four river flow stations Berg@Franschoek, Bree@Ceres, Wit River@Drosterkloof and Little Berg@Nieuwkloof) are stronger for shorter periods (i.e. 1987–2017 and 2007–2017) than that for the longer period, 1960–2017. The Intergovernmental Panel on Climate Change emphasises the importance of studies to assist with model prediction uncertainties. To this end, our study expands the understanding of regional hydrological responses to rainfall change in the water stressed region of the Western Cape Province.
 Significance:
 
 Historical trend analyses provide the basis for future rainfall and river flow projections and also improve our understanding of hydrological responses to rainfall change, which is important for water resource planning and management in light of recent rainfall shortages experienced in the Western Cape region.
 Anthropogenic and natural influences on river systems must be taken into account when assessing the impact of rainfall changes on river flow because these factors ultimately affect water resource management.
 We identified decreasing winter rainfall trends across the Western Cape Province for the most recent three decades.

The competing impacts of climate change and nutrient reductions on dissolved oxygen in Chesapeake Bay

Abstract. The Chesapeake Bay region is projected to experience changes in temperature, sea level, and precipitation as a result of climate change. This research uses an estuarine-watershed hydrodynamic–biogeochemical modeling system along with projected mid-21st-century changes in temperature, freshwater flow, and sea level rise to explore the impact climate change may have on future Chesapeake Bay dissolved-oxygen (DO) concentrations and the potential success of nutrient reductions in attaining mandated estuarine water quality improvements. Results indicate that warming bay waters will decrease oxygen solubility year-round, while also increasing oxygen utilization via respiration and remineralization, primarily impacting bottom oxygen in the spring. Rising sea level will increase estuarine circulation, reducing residence time in bottom waters and increasing stratification. As a result, oxygen concentrations in bottom waters are projected to increase, while oxygen concentrations at mid-depths (3 < DO < 5 mg L−1) will typically decrease. Changes in precipitation are projected to deliver higher winter and spring freshwater flow and nutrient loads, fueling increased primary production. Together, these multiple climate impacts will lower DO throughout the Chesapeake Bay and negatively impact progress towards meeting water quality standards associated with the Chesapeake Bay Total Maximum Daily Load. However, this research also shows that the potential impacts of climate change will be significantly smaller than improvements in DO expected in response to the required nutrient reductions, especially at the anoxic and hypoxic levels. Overall, increased temperature exhibits the strongest control on the change in future DO concentrations, primarily due to decreased solubility, while sea level rise is expected to exert a small positive impact and increased winter river flow is anticipated to exert a small negative impact.

Sea level rise impacts on rice production: The Ebro Delta as an example

Climate change and sea level rise (SLR) are global impacts threatening the sustainability of coastal territories and valuable ecosystems such as deltas. The Ebro Delta is representative of the vulnerability of coastal areas to SLR. Rice cultivation is the main economic activity in the region. Rice fields occupy most of the delta (ca. 65%) and are vulnerable to accelerated SLR and consequent increase in soil salinity, the most important physical factor affecting rice production. We developed a model to predict the impacts of SLR on soil salinity and rice production under different scenarios predicted by the Fifth Assessment Report of the Intergovernmental Panel on Climate Change by coupling data from Geographic Information Systems with Generalized Linear Models. Soil salinity data were measured in agricultural parcels and rice production from surveys among farmers. The correlation between observed and soil salinity predicted values was high and significant (Pearson's r=0.72, P<0.0001), thus supporting the predictive ability of the model. Soil salinity was directly related to distances to the river, to the delta inner border, and to the river old mouth, while clay presence, winter river flow and surface elevation were inversely related to it. Surface elevation was the most important variable in explaining soil salinity. Rice production was negatively influenced by soil salinity, thus the models predict a decrease from higher elevation zones close to the river to the shoreline. The model predicts a maximum reduction in normalized rice production index from 61.2% in 2010 to 33.8% by 2100 in the worst considered scenario (SLR=1.8m), with a decrease of profit up to 300 € per hectare. The model can be applied to other deltaic areas worldwide, and help rice farmers and stakeholders to identify the most vulnerable areas to SLR impacts.

Impact of forest fires on the concentrations of polychlorinated dibenzo-p-dioxin and dibenzofurans in coastal waters of central Chile

The relationship between the occurrence of forest fires in central Chile and the total concentration of dioxins and furans (PCDD/F) in nearby coastal waters was analyzed. The data for this analysis was obtained from a long-term environmental monitoring program (PROMNA) in the Bio-Bio Region. Quantification of PCDD/F was performed using HRGC/HRMS at the MSS laboratory in England. Between 2006 and 2014, peaks were observed in February 2007 and 2012. These concentration maxima coincided with major forest fires in the Bio-Bio Region and particularly with those in the Itata River Basin. The January 2012 fires generated an intense short-term response that was associated with atmospheric transport which increases medium toxicity furan-type congeners concentrations (TCDF, PCDF and HxCDF) and six months later a concentration increase of low toxicity dioxin-type congeners was observed (OCDD, HpCDD and HxCDD) coinciding with maximum winter river flow. These results suggest that forest fires near the coastal zone are responsible for increases in PCDD/F concentration observed in the study area.

Influência da Oscilação do Atlântico Norte no clima do continente europeu e no caudal dos rios ibéricos atlânticos

THE IMPACT OF THE NORTH ATLANTIC OSCILLATION ON THE EUROPEAN CLIMATE AND RIVER FLOW OF THREE MAJOR IBERIAN RIVERS – The North Atlantic Oscillation (NAO) is the most dominant mode of atmospheric circulation variability over the entire Northern Hemisphere (NH) and has recently been shown to be related to climate over large regions of the NH, in particular, over the European and North American continents. Here, a multivariable analysis of the influence ofthe NAO on the climate of the North Atlantic and European sectors is presented using the 40 year (1958-97) reanalysis data set from National Centres for Environmental Prediction. Using high and low NAO index composites, anomaly fields of climate variables are then interpreted based on physical mechanisms associated with the anomalous mean flow (characterised by the surface wind field) and theanomalous eddy activity (characterised by the surface vorticity and the 500hPa storm track fields). It is shown that NAO-related temperature patterns are mainly controlled by the advection of heat by the anomalous mean flow. However, asymmetries between minimum and maximum temperatures, and more significantly, between positive and negative phases of NAO imply the importance of a different mechanism, namely the modulation of short wave and long wave radiation by cloud cover variations associated with the NAO. Furthermore, NAO influence over two different precipitation-related variables, namely, precipitation rate and precipitable water display different patterns. Precipitable water is shown to be strongly related to the corresponding anomaly fields of temperature while precipitation rate appears to be controlled by the surface vorticity field and associated strength of the tropospheric synoptic activity. Finally, we have assessed the impact of the NAO on winter river flow regimes for several different Portuguese rivers, including the three main international Iberian rivers, the Douro (north), the Tagus (centre) and the Guadiana (south). Results show that the large inter-annual variability of flow of these three rivers is largely modulated by the NAO. Such modulation, associated with the recent positive trend of the NAO index, might implicate a significant decrease of the available flow. This reduction can representan important hazard for the Portuguese economy due to its negative impact in agricultural yield and hydroelectric power production.

Quantifying the Predictability of Winter River Flow in Iberia. Part I: Interannual Predictability

Abstract The interannual variability and predictability of the winter streamflow of the main Iberian Peninsula international rivers (Douro, Tejo, and Guadiana) are examined for the period 1923–2004. In the first part of this paper, a singular spectral analysis was carried out to isolate the main oscillatory components of the streamflow series. Results showed a similar model structure for the three rivers, including the following components: (i) a nonlinear trend that contains variability at periods of 20–30 yr, (ii) modulated amplitude oscillations with associated periods in the bands 2–3, 4–5, and 6–8 yr, and (iii) a red noise process. These models accounts for the bulk of winter river flow variance, ranging between 64% (Guadiana) and 96% (Douro). In general, the amount of variability associated with the low-frequency component is similar to that associated with the interannual variability. The analysis of the association between the North Atlantic Oscillation (NAO) and the streamflow variability proved this relationship to be complex and nonstationary. In particular, it is found that only when the NAO presents high amplitude oscillations is this mode capable of dominating the streamflow variability. In Part II, autoregressive-moving-average (ARMA) models were fitted to the filtered streamflow series and an interannual forecasting experiment was conducted. Results were tested against the raw streamflow series. The percentage of variance explained by the models ranged from 25% to 62%. Additionally, the ARMA models presented useful one-year-ahead forecasting skills. Particularly during the validation period (1986–2004) the models performed between 51% and 53% better than climatology. The skill against persistence proved to be much greater, indicating that the climatology is a better benchmark than persistence for streamflow forecasting in Iberia. Finally, the developed models were, in most cases, able to accurately predict the phase of the streamflow, with a percentage of agreement that ranged from 54% to 90% throughout the validation period.

Quantifying the Predictability of Winter River Flow in Iberia. Part II: Seasonal Predictability

Abstract The role of the Atlantic summer and autumn SSTs on the predictability of the winter Iberian Peninsula river flows is analyzed during the period 1923–2004. The analysis is based on the results of an interannual predictability experiment, using autoregressive-moving-average (ARMA) models, carried out in the first part of this work. A standard principal component analysis (PCA) was applied to the summer and autumn SST fields for the entire Atlantic Ocean. Then, the association between the resulting principal component (PC) series and the Iberian Peninsula streamflow series was analyzed, in order to use the PC series as additional predictor variables in a seasonal forecasting regression model. Results proved, first, that during autumn, the SST variability in the so-called North Atlantic horseshoe pattern has a statistically significant linear influence in the following winter streamflow values. In particular, the use of this SST information considerably improves the skill of the linear forecast (improvements against climatology range from 61% to 90%) compared to the ARMA-alone model (51%–53%). These improvements are mostly related to the ability of the SST information to provide better estimates of extreme streamflow values. Additionally, results showed that the summer tropical Atlantic and the autumn southwestern Atlantic SST variability have a significant nonlinear influence on the following winter streamflow values. In particular, there is a tendency for negative streamflow anomalies following tropical Atlantic summer negative SST anomalies and following southwestern Atlantic autumn SST positive anomalies. It is finally concluded that the linear interannual predictability of the Iberian Peninsula winter streamflow is greater (two-thirds of the total predictability) than the predictability associated with the previous season autumn SSTs (one-third).

Bacterial indicators of faecal pollution in the waters of the El‐Kabir River and Akkar watershed in Syria and Lebanon

AbstractWater samples for bacterial analyses were taken, when possible, at 41 sites in Lebanon and Syria in the El‐Kabir River watershed. Samples were analysed for total coliform (TC), faecal coliform (FC) and faecal streptococcus. The Lebanese samples also were analysed for the presence of sulphate‐reducing bacteria. The TC and FC concentrations were extremely high throughout the watershed, rendering the water unfit for any human uses. The origin of the bacteria is the untreated sewage waste from the numerous settlements situated throughout the watershed. This primary origin is supported by high ratios of FC/faecal streptococcus, although impacts from animal wastes also were observed. The bacterial levels were higher in summer than in winter, indicating a high winter river flow that dilutes a relatively constant source of human sewage discharged to the system. Spring waters also exhibited elevated levels of bacteria, implicating surface land use and waste disposal practices upstream of the springs. The data clearly shows that human health is at a high risk and that strategies for improving water quality and protecting spring water must be expeditiously implemented.

North Atlantic oscillation influence on precipitation, river flow and water resources in the Iberian Peninsula

AbstractThe Iberian Peninsula precipitation and river flow regimes are characterized by large values of inter‐annual variability, with large disparities between wet and dry years, especially in southern Iberia. This situation is a major problem for water resources management in general, and for the production of hydroelectricity in particular. Hydroelectric production represents, in an average year of precipitation, 20% of the total Spanish electricity production (and 35% for Portuguese production). Its absolute value, however, can vary by a factor of three between wet and dry years. We have assessed the impact of the North Atlantic oscillation (NAO) on winter precipitation and river flow regimes for the three main international Iberian river basins, namely the Douro (north), the Tejo (centre) and the Guadiana (south). Results show that the large inter‐annual variability in the flows of these three rivers is largely modulated by the NAO phenomenon. Throughout most of the 20th century, the January‐to‐March river flow is better correlated with the December to February (DJF) NAO index than is the simultaneous (DJF) river flow. Correlation values for the period 1973–98 are highly significant (−0.76 for Douro, −0.77 for Tejo and −0.79 for Guadiana), being consistently of higher magnitude than those obtained over previous decades. This impact of the NAO on winter river flow was quantified in terms of total Spanish potential hydroelectricity production. The important control exerted by the NAO and the recent positive trend in the NAO index contribute to a significant decrease in the available flow. This reduction represents an important hazard for the two Iberian economies because of its negative impact on water‐dependent resources, such as intensive agriculture and hydroelectric power production. Copyright © 2004 Royal Meteorological Society

Flushing of dense, hypoxic water from a cavity of the Swan River estuary, Western Australia

Flushing of dense water from cavities of the upper reaches of the Swan River estuary in Western Australia was investigated using measured salinity and dissolved oxygen profiles and a two-dimensional, laterally averaged hydrodynamic model (TISAT). Seasonal flushing of dense, hypoxic bottom waters from a relatively deep site took place over ∼3 days at the onset of winter in 1994. Model simulations of the purging of this dense water did not correspond closely with changes in the densimetric Froude number. Purging, expressed as depth of the halocline as a fraction of the total cavity depth, occurred when the simulated mean horizontal velocity at 2 m depth (top of cavity) changed from negative to strongly positive, indicating arrest of upstream flow and continuous downstream flow. This corresponded to freshwater discharge of about 50 m3 s−1. Oxygen depletion of bottom waters was closely related to stratification. Oxygen dynamics at the onset of winter river flow was analysed using an exponential decay model, assuning that there was no net inflow or outflow across the halocline and thus no vertical transport of oxygen during a period of strong stratification. The rate constant for oxygen decay at Ron Courtney Island (RCI) was estimated to be 0.232 d−1 for this period. Bottom waters at RCI declined to less than 1 mg 1−1 prior to complete flushing through increased river flows. This study provided in sights to how freshwater flows may be allocated to maintain suitable oxygen levels in the bottom waters of estuarine cavities.