bluuebunny/crossref_metadata_2025 huggingface dataset:
Long-Term Analysis and Short-Term Forecasting of Dry Spells by Palmer Drought Severity Index
Authors: Lohani V. K. , Loganathan G. V. , Mostaghimi S.
Published: May 2018

This paper presents a non-homogeneous Markov chain approach for analyzing drought characteristics using the Palmer Drought Severity Index (PDSI). The probability mass functions of occurrence of different drought severity classes, their durations, and times of return to a particular drought class are obtained and are in turn utilized to generate the needed statistics and forecasts. Two methods of forecasting drought severity classes for one, two, and three months lead times are put forward. The methodology is applied to ninety six years of PDSI data corresponding to two climatic divisions in Virginia, USA. Comparison between the analytical results and the empirical estimates supports the utility of the method. The method can be used in a planning mode for developing buffer storage in drought prone regions and in an operational mode for optimal rationing of water among competing needs as drought progresses.
Spatial Analysis of Rainfall in Southwest of Saudi Arabia using GIS
Authors: Taher Saud , Alshaikh Abdulmohsin
Published: May 2018

A Geographic Information System was used to study the characteristics and distribution of precipitation in southwest of Saudi Arabia based on a number of influencing factors including elevation, mountain slope and orientation, distance from moisture source and equator, wind direction, and geographic location. Results indicate that elevation explains about 25% of variability in precipitation in most of the seasons. Other factors such as aspect, slope, distance from moisture source have different effects but less than the effect of elevation. Finally a polynomial trend surface has been generated to correlate geographic location with precipitation and has shown a coefficient of determination of 70%.
Snowmelt Hydrology of Two Subarctic Slopes, Southern Yukon, Canada
Authors: Carey Sean K. , Woo Ming-ko
Published: May 2018

Large quantities of water are discharged from subarctic basins during snowmelt season. Runoff contributing areas as well as timing and magnitude of meltwater generation from different slopes are highly variable. Two slopes in the lower Wolf Creek basin, southern Yukon, were studied in 1997. The south-facing slope has a dense aspen forest that is leafless in the melt period (April – May) and is underlain by seasonal frost. The north-facing slope has open stands of spruce and an organic layer that rests on mineral soils with permafrost. In 1997, snowmelt is advanced by over 10 days on the south slope, which receives more solar radiation than the north aspect. All meltwater on the south slope infiltrates the frozen silt without generating runoff. By the time significant melt events occur on the north slope the frost and snow are gone from the south. Meltwater is able to infiltrate the frozen organic soil but deep percolation is prevented by the ice-rich substrate. Lateral flow begins after the organic layer is saturated, with much runoff along intermittent rills fed by diffuse and pipe flows. Rills and pipes are interconnected but the drainage network and runoff contributing area change depending on the disposition of the snow as well as water and frost table positions relative to local topography. Contrasts between the north and south slopes have important implications on direct runoff generation during the melt period. Situations similar to the study site can be found elsewhere in subarctic North America and the observed processes have a bearing upon hydrological modelling for the subarctic environment.
The Effect of Climate Change on River Flow and Snow Cover in the NOPEX Area Simulated by a Simple Water Balance Model
Authors: Xu C-Y , Halldin Sven
Published: May 2018

Within the next few decades, changes in global temperature and precipitation patterns may appear, especially at high latitudes. A simple monthly water-balance model of the NOPEX basins was developed and used for the purposes of investigating the effects on water availability of changes in climate. Eleven case study catchments were used together with a number of climate change scenarios. The effects of climate change on average annual runoff depended on the ratio of average annual runoff to average annual precipitation, with the greatest sensitivity in the catchments with lowest runoff coefficients. A 20% increase in annual precipitation resulted in an increase in annual runoff ranging from 31% to 51%. The greatest changes in monthly runoff were in winter (from December to March) whereas the smallest changes were found in summer. The time of the highest spring flow changed from April to March. An increase in temperature by 4°C greatly shortened the time of snow cover and the snow accumulation period. The maximum amount of snow during these short winters diminished by 50% for the NOPEX area even with an assumed increase of total precipitation by 20%.
In Situ Measurements in Fractured Till Using Sidewall Sensors
Authors: Murdoch Larry , Harrar Bill , Nilsson Bertel , Slack William , Siegrist Robert
Published: May 2018

Subsurface parameters, such as hydraulic head, often vary markedly with depth in fine-grained glacial sediments, but sensors placed in vertical boreholes are poorly suited to resolve these variations. One problem is that conventional methods only allow one, or perhaps a few, sensors to be placed in each borehole. To address such limitations we have developed a method for accessing the sidewall of a borehole. The method uses a device that pushes sensors or sediment samplers laterally into the sidewall to distances slightly less than the diameter of the borehole. The device can obtain a core sample 15 cm long and 4 cm in diameter, and then insert a permeable sleeve for extracting water samples. The same device has been used to insert several types of electrodes capable of measuring water content (using TDR waveguides), Eh (using platinum electrodes), or electrical resistivity (using a miniature Wenner-type array). At a site near Flakkebjerg, Denmark, we installed 22 water samplers and 19 resistivity electrodes in a single borehole to measure hydraulic head gradients in detail and to monitor the vertical migration of ionic tracers. This approach can be used to install horizontally oriented TDR waveguides at virtually any depth, thereby extending the TDR technique to the study of deep vadose zones. At a contaminated site in the USA, TDR wave guides were installed to a depth of 12 m in glacial till. Other applications include measurement of Eh at a site where in situ chemical oxidization was used, and the in situ sensors provided results that are similar to data obtained from soil cores.
Model Sophistication in Relation to Scales in Snowmelt Runoff Modeling
Authors: Bengtsson Lars , Singh Vijay P.
Published: May 2018

Snowmelt induced runoff from river basins is usually successfully simulated using a simple degree-day approach and conceptual rainfall-runoff models. Fluctuations within the day can not be described by such crude approaches. In the present paper, it is investigated which degree of sophistication is required in snow models and runoff models to resolve the basin runoff from basins of different character, and also how snow models and runoff models must adapt to each other. Models of different degree of sophistication are tested on basins ranging from 6,000 km2 down to less than 1 km2. It is found that for large basins it is sufficient to use a very simple runoff module and a degree day approach, but that the snow model has to be distributed related to land cover and topography. Also for small forested basins, where most of the stream flow is of groundwater origin, the degree-day method combined with a conceptual runoff model reproduces the snowmelt induced runoff well. Where overland flow takes place, a high resolution snow model is required for resolving the runoff fluctuations at the basin outlet.
Assessment of Variability in Fluvial Sediment Transfers in Kärkevagge (N-Sweden) during the last 50 Years
Authors: Gude Martin , Jonasson Christer , Dietrich Susanne , Scherer Dieter
Published: May 2018

The Kärkevagge (Abisko area, Northern Sweden) represents a focus research basin concerning geomorphic processes and sediment budgets for the last 50 years. Different geomorphic process studies provide comparative data sets concerning climate variability implications on sediment transfers. While monitoring of sediment transfers is discontinuous with respect to study periods and methods, a detailed chronology of high-magnitude events with significant sediment displacement is available. In continuation of these studies, investigations in 1995 and 1998 as part of the MOSAIC project (Modelling Of Snowmelt And Its Consequences) are concentrating on snowmelt-induced slushflow initiation and transports of sediments in several small headwater catchments during the snowmelt period. Main purpose of the investigations is to characterize different catchment sections in terms of their hydrologic and sedimentologic contribution to the total fluvial and sediment budget of the basin, and to evaluate their specific sensitivity related to changes in atmospheric boundary conditions. By means of these data sets, the temporal variability of fluvial sediment transfers can be assessed over different time scales. The paper focuses on a description of different sections in the fluvial sediment transfer system in Kärkevagge. By comparing results from recent field investigations with data from former studies, the significance of rainfall- and snowmelt-triggered events for sediment transfers is evaluated.
Slushflow Hazard and Mitigation in Vesturbyggd, Northwest Iceland
Authors: Tómasson Gunnar Gudni , Hestnes Erik
Published: May 2018

Slushflows – flowing mixtures of water and snow – threaten several residential areas within Vesturbyggð, a municipality of 1250 people located in the Vestfirdir peninsula in Northwest Iceland. An overview of the problem is given and particular attention is drawn to the catastrophic events of January 22nd 1983 in Patreksfjörður, when two slushflows damaged or destroyed 20 houses, killing four of the twelve people caught in the them. As the runout zones of the slushflows are densely populated the local authority requested an appraisal study for slushflow defences. For the main hazard zone below Geirseyrargil the work included an evaluation of potential starting zones, hazard areas, mitigative measures and cost estimates compared with the value of the involved properties.

Slushflow activity in Vesturbyggð and other parts of Iceland is associated with cyclonic activity during winter as well as spring break-up periods. Most commonly, slushflows are released in drainage channels and streams, but they may also start from inclined depressions. Snow-embanked, water-saturated snowfields are other potential starting zones. Whether a snowpack will reach a critical stability during rain and snowmelt depends on the complex interaction between geomorphic factors, snowpack properties and the relative rate of formation and discharge of free water in the snowpack in potential starting zones. By analysis of meteorological records from the autumn of 1982 and January of 1983 the snowpack development prior to the events and stability of the snowpack at the start of the critical weather period in January 1983 are estimated.
Interception of a Dense Spruce Forest, Performance of a Simplified Canopy Water Balance Model
Authors: Alavi Ghasem , Jansson Per-Erik , Hällgren Jan-Erik , Bergholm Johan
Published: May 2018

The process of interception was studied in 25-year-old dense stands of Norway spruce in South Sweden. The throughfall was measured intensively during one month and extensively during four growing seasons using water captured by large roofs and with randomly distributed funnel gauges. It was found that about 45% of the precipitation was lost as interception loss from this dense forest canopy. However, many sources of potential error, particularly in measurement of precipitation and throughfall, may be involved in quantifying the interception loss. The data set was used to test the interception part of a hydrological model, SOIL. The model uses a simple threshold formulation to calculate the accumulation of intercepted water in a single storage variable. The model was able to estimate fairly well the long-term cumulative interception loss from the forest canopy However, similarly to many other models, SOIL showed a pattern of overestimation of the interception loss during events with small precipitation and underestimation during events with large precipitation. It was concluded that the storage capacity was of major importance in modelling of long-term interception loss. Tree canopy water storage capacity on a leaf area basis was estimated to 0.7 mm which was three times larger than that obtained from a precipitation/throughfall graph.
Experimental Hydrological Analyses in the Dischma based on Daily and Seasonal Evaporation
Authors: de Jong Carmen , List Franz K. , Ergenzinger Peter J.
Published: May 2018

The Dischma is a typical high mountain valley in the alpine source area of the River Rhine. A knowledge of the daily and seasonal water balance is important for understanding and predicting the effects of climatic fluctuations on river discharge. Traditional methods of analysing the water cycle usually involve deriving evaporation from precipitation and discharge. However, in mountain regions single station precipitation and discharge data cannot simply be extrapolated to represent regional evaporation characteristics. Measurements of precipitation in mountains are both limited in accuracy and spatial representativeness in contrast to well-defined discharge data. Field measurements of evaporation in the Dischma valley recorded over five summers give a fairly accurate picture of this component over space and time. New results on the characteristics of evaporation, transpiration and condensation are obtained from automated evaporation pans, lysimeters and climatological stations. The water cycle can be defined with greater precision by measuring discharge and evaporation and deriving precipitation than the more traditional technique of deriving evaporation.
Association Between Ice Conditions in the Baltic Sea along the Estonian Coast and the North Atlantic Oscillation
Authors: Jevrejeva Svetlana
Published: May 2018

Variations in time series of sum of negative degree-days, number of days with ice, date of ice break-up and maximum ice thickness on the Baltic Sea along the Estonian coast have been examined within context of the atmospheric circulation above the North Atlantic. It was found out that 20 – 50 % of ice conditions along the Estonian coast might be explained by the state of the NAO winter index. However, correlation coefficients between time series of ice conditions and the NAO winter index varies with time; moving correlation coefficient can reach -0.98.
Rainfall Runoff Modelling Based on Genetic Programming
Authors: Babovic Vladan , Keijzer Maarten
Published: May 2018

The runoff formation process is believed to be highly non-linear, time varying, spatially distributed, and not easily described by simple models. Considerable time and effort has been directed to model this process, and many hydrologic models have been built specifically for this purpose. All of them, however, require significant amounts of data for their respective calibration and validation. Using physical models raises issues of collecting the appropriate data with sufficient accuracy. In most cases it is difficult to collect all the data necessary for such a model.

By using data driven models such as genetic programming (GP), one can attempt to model runoff on the basis of available hydrometeorological data. This work addresses use of genetic programming for creating rainfall-runoff models on the basis of data alone, as well as in combination with conceptual models (i.e taking advantage of knowledge about the problem domain).
Water and Nutrient Budgeting of Rostherne Mere, Cheshire, UK
Authors: Krivtsovi V. , Bellinger E. , Sigee D.
Published: May 2018

This paper presents a simple model of the Rostherne Mere water catchment. The model allows calculation of water and elemental budgets on meteorological data using regressions derived from a monitoring data set. Estimates of yearly inputs and outputs of Ca, Mg, K and N suggest that the lake is currently acting as a sink for these elements. Comparison with earlier estimates shows an increase in N loading. High inputs of particulate P appear to be balanced by outputs of inorganic P, suggesting that the two may be coupled by certain physical and biogeochemical processes within the lake ecosystem, including adsorption to/desorption from particles, coprecipitation with various chemical compounds, uptake and excretion by biota, mineralisation and release from sediments.
Winter-Season Climatic Signals in the Recently Deposited Snowpack on a Norwegian Alpine Glacier
Authors: Yuanqing He , Theakstone Wilfred H. , Tandong Yao , Guodong Cheng , Dian Zhang , Meixue Yang
Published: May 2018

Vertical variations of oxygen isotopes in the snow which accumulates during the winter at the Norwegian glacier Austre Okstindbreen are not entirely eliminated after 1-2 months of ablation in the following summer. Survival of isotopic signals closely relates to the re-freezing capacity of snow accumulated in winter when its temperature was below 0°C. The meltwater re-freezes in layers formed in winter hindered subsequent meltwater percolation in summer when snow temperature was at melting point and, therefore, varied isotopic record was reserved between these ice layers. The isotopic record in snowpack can provide an estimate of the approximate trend of the most recent winter season temperatures. The relationship between regional temperature changes and б18O values in the snowpack is affected by many natural factors, but 1989-90 (a glacier balance year) winter air temperatures were reflected in the snow which remained on the glacier Austre Okstindbreen at an altitude of 1,350 m in July 1990. There was larger amplitude of variations of б 18O values in the 4.1 m of snow above the 1989 summer surface, but variations in the underlying firn were relatively small. Meltwater percolation modifies the initial variations of б 18O values in the snowpack. At a site below the mean equilibrium line altitude on Austre Okstindbreen, increased isotopic homogenization within a ten-day period in July accompanied an increase of the mean б 18O value. Although the isotopic record at a temperate glacier is likely to be influenced by more factors than is that at polar glaciers, it can provide an estimate of the approximate trend of recent local temperature variations.
Calculating Irradiance Penetration into Water Bodies from the Measured Beam Attenuation Coefficient, II: Application of the Improved Model to Different Types of Lakes
Authors: Arst Helgi , Erm Ants , Reinart Anu , Sipelgas Liis , Herlevi Antti
Published: May 2018

The method suggested earlier for estimating the spectra of diffuse attenuation coefficient of light in the water bodies relying on the beam attenuation coefficient measured from water samples, was improved and applied to different types of lakes. Measurement data obtained in 1994-95 and 1997-98 for 18 Estonian and Finnish lakes were used. The spectra of two characteristics were available for our investigations: 1) beam attenuation coefficient estimated from water samples in the laboratory with a spectrophotometer Hitachi U1000; 2) vertical irradiance (diffuse) attenuation coefficient measured in situ with an underwater spectroradiometer LI 1800UW. A total of 70 spectra were considered. Relying on these data the parameters of our earlier model were changed. The criterion of the efficiency of the new version of our model is the coincidence of the spectra of diffuse attenuation coefficient derived from Hitachi U1000 data (Kdc) with those obtained by underwater irradiance measurements (Kdm). Correlation analysis of the model's results gave the relationship Kdm=1.0023Kdc with correlation coefficient 0.961. The respective values of mean relative difference and standard deviation were 5.4% and 0.55 m−1. This method may be useful in conditions where in situ measuring of underwater irradiance spectra cannot be performed because of weather conditions. As the measurement of the underwater radiation field is often a complicated and expensive procedure, our numerical method may be useful for estimating the underwater light climate.
Ice Conditions along the Estonian Coast in a Statistical View
Authors: Jevrejeva Svetlana , Leppäranta Matti
Published: May 2018

The paper presents the results from analysis of long-term (100-year) time series of freezing, fast ice formation, disappearance of fast ice, break-up and ice thickness for eight stations situated along the Estonian coast in the Gulf of Finland and Gulf of Riga. Most of the data have not been published yet. Basic statistics: average, standard deviation, maximum, minimum and frequency histograms are given. On average ice has formed in the Gulf of Finland three weeks later compared with the Gulf of Riga. The range of variation of the freezing date is very large, 3-4 months, with maximum value of standard deviation 29 days (Tallinn). The average ice seasons last 4-5 months; the range is 0- 7 months. Statistically significant trends are found in time series of date of freezing for Sõrve and Virtsu and in time series of ice break-up for Kihnu and Virtsu, both trends toward shorter ice seasons. Correlation coefficients of different time series are varied through 0.03-0.90.
Dynamics of River Flow Regimes Viewed through Attractors
Authors: Krasovskaia Irina , Gottschalk Lars , Leblois Etienne , Sauquet Erik
Published: May 2018

Analysing complicated systems we must never forget that the extraordinary increase in the rate of progress in our understanding can tell us nothing about the state of our knowledge.

H.Metzger (1994)

The hydrological system is extremely complex. To get insight into its behaviour and possible future states it is important to assess not only its individual components but also consider their interaction. Studying the hydrological system in its context allows focusing on the inherent patterns of its behaviour and search for external rules of its functioning. Changing climate can alter the seasonality of river flow, increasing the frequency of some patterns and decreasing that of the other, which can be adequately described in probabilistic terms. Dimensionality reduction facilitates to discern the patterns present in high dimensional systems. The approach suggested herein allows studying the dynamics of river flow seasonality patterns in the context of the present hydrological system in terms of the probability density functions of the weight coefficients in the reduced phase space, using Principal Components for dimensionality reduction. The approach is presented on the example of a large sample of monthly runoff series for Scandinavia and France, which gives a possibility to identify some common features in the dynamics of seasonality of river flow across a vast region of Europe.
Modelling the Effect of the Hydroelectric Pumped Storage Plant on Hydrodynamic Regime of the Kaunas Reservoir In Lithuania
Authors: Gailiusis Brunonas , Kriauciuniene Jurate , Rimaviciute Erika
Published: May 2018

The Kaunas Reservoir was formed during construction of the Kaunas Hydroelectric Plant (Kaunas HP) on the Nemunas River in 1960. Since 1992 it has also been serving as a lower reservoir for the Kruonis Hydroelectric Pumped-Storage Plant (Kruonis HPP), which currently has four generating units with 200 MW of installed capacity each. There are plans to increase the capacity of this power plant by constructing additional four generating units. Operation of the Kruonis HPP is already changing the hydrophysical regime (water levels and flow velocities) of the Kaunas Reservoir and new units can seriously aggravate the situation by inducing bottom erosion. The objective of this study is to determine the optimal number of generating units so that the impact of the Kruonis HPP on the hydrophysical regime of the reservoir would be acceptable. The hydrodynamic model MIKE 21 was used to calculate the flow velocity and water level fluctuation in the Kaunas reservoir for different number of the Kruonis HPP generating units. The Kaunas HP was considered as operating with minimal load or under conditions equivalent to a big flood (2,000 m3/s). The modelling results indicate that the impact of four units is acceptable while simultaneous operation of the eight units at Kruonis HPP would not be desirable.
Simulation of a Biogeochemical Model in Different Lakes
Authors: Pers Bodil Charlotta , Persson Irina
Published: May 2018

Eutrophication, caused by nutrients leached from soil and emitted from point sources, is a well-known problem in many Swedish lakes. There are several countermeasures that can be used to reduce eutrophication. A model that can simulate the biogeochemical response to different management scenarios may help with nutrient reducing strategies. Results from applications with such a model to different types of lakes are presented in this paper.

The most important variables simulated by the model are dissolved nutrient concentrations (nitrogen and phosphorus) and phytoplankton. Other variables include nitrogen fixating cyanobacteria, sediments, and zooplankton. In total, 14 state variables are simulated. Nutrients are supplied through tributaries, and the temperature and vertical mixing forced by meteorological input.

The model is able to simulate effects of changing nutrients and plankton dynamics. It is promising as an instrument for evaluating various measures to improve water quality in lakes. However, for the lakes the model has been applied to, the model has been calibrated to available observations. Non-monitored lakes could also be interesting to simulate, therefore the parameters of the model set-ups are discussed in this paper.
Water Chemistry and Bacterioplankton in Two Subalpine Rivers in Finnish Lapland
Authors: Huitu Eeva , Arvola Lauri
Published: May 2018

Water chemistry and bacterioplankton were analysed for two subalpine rivers, River Kidisjoki and River Utsjoki, in northernmost Finland. The data set is based on continuous runoff measurements and weekly chemical and biological samples. The data were collected during the open water period, from May to October, in year 2000. The runoff patterns during the summer were similar in the two rivers at though the size of the catchments is very different (the catchment of River Utsjoki 1,520 km2 and of River Kidisjoki 22 km2). For both rivers, variations in runoff were followed by variations in the water quality and bacterial densities. The measured chemical concentrations were usually the highest in the headwaters of river Kidisjoki, while in the lower Kidisjoki they were clearly lower than in Utsjoki. Bacterial densities were on average highest in Utsjoki and the strongest relationships between water chemistry and bacteria were found in Kidisjoki. Both the chemical concentrations and bacterial densities were low in the two rivers when compared to other studied rivers in northern Finland.
Flow categorization model for improving forecasting
Authors: Sivapragasam C. , Liong Shie-Yui
Published: May 2018

Prediction of high magnitude flows is of interest in many hydrological applications such as operation of flood control reservoirs, flood forecasting and gated spillways. Of the various types of existing streamflow prediction approaches, data driven models (such as ANN) are increasingly being preferred over the traditional conceptual models due to their simplicity, fast speed and ease of use. For models that consider only historical streamflow data, an attempt has been made to design a robust model over a wide range of streamflow magnitudes. The model inputs are the immediate past streamflow data which generally do not predict the typically high flows well, particularly for large lead times.

In this study, the flow range is divided into three regions (low, medium and high flow regions) and the attributes are decided based on the underlying hydrological process of the flow region. A flow forecasting model is applied for each flow region, using only the historical streamflow data as input. The proposed approach is implemented in Tryggevælde Catchment (Denmark) for 1- and 3-lead days, using the Support Vector Machine (SVM), which yields promising results, particularly for high flows in a 3-lead day model.
The use of design elements in wetlands
Authors: Persson J.
Published: May 2018

In literature on wetland design it is often recommended to use design elements to improve the hydraulic performance, which is linked to the pollutant removal efficiency. To investigate the effect these elements have on the hydraulic performance, a case study was carried out on two wetlands located in southern Sweden. The two main questions of the study were how the performance differs between the two wetlands and how it is affected by the use of deep zones and islands. Field measurements and computer simulations were carried out to obtain residence time distributions (RTD) and flow patterns. As analytical parameters, normalized peak time and effective volume ratio were used to interpret the results. The conclusion is that islands and deep zones as design elements can improve the hydraulic performance, but also that it is important to use them wisely. In one of the wetlands, the bad location of several islands led to severe short-circuiting and large areas of dead zones.
Regional flow duration curve for a Himalayan river Chenab
Authors: Arora Manohar , Goel N.K. , Singh Pratap , Singh R.D.
Published: May 2018

This study is carried out with the objective of examining the effect of altitude on water availability estimates for the various sub-basins of the Chenab river basin (mean elevation of the basin is 3600 m), which is a snow-fed Himalayan river basin located in the western Himalayas. This basin covers all three Himalayan ranges, i.e. outer, middle and greater Himalayas. For this study, the daily flow data of 11 gauging sites varying from 14 years to 23 years in the Chenab river basin are utilised. The other important information related to the physiography, hydrology and meteorology, etc, for the region are derived from the available literature and maps. The daily flow data of nine gauging sites are utilised for developing the regional relationships for water availability computations. These relationships are tested over the remaining two gauging sites. The regional relationships are developed using three different approaches. These approaches include: (i) parameter regionalisation for individual gauged sites of selected probability distribution, (ii) regionalisation of dependable flows and (iii) parameter regionalisation for the region as a whole of the selected probability distribution. The different methods are compared and discussed in detail. It is observed that the flow for a given dependability increases with catchment area and decreases with altitude. The flows of the catchments at higher altitudes exhibit larger variability in comparison to the catchments at lower altitudes. The regional relationships are recommended for the use of field engineers.
The realism of the ECHAM5 models to simulate the hydrological cycle in the Arctic and North European area
Authors: Arpe Klaus , Hagemann Stefan , Jacob Daniela , Roeckner Erich
Published: May 2018

A new version of the ECHAM model is investigated in respect of the hydrological cycle in the Arctic and North European area. Several horizontal and two vertical resolution versions are studied. The higher-resolution ECHAM5 models are, in many respects, superior to the lower-resolution versions of the same model family and the older ECHAM4 model. The vertical resolution has a decisive impact but also increased horizontal resolution leads mostly to improvements. Here T106 (about 110 km) often gives the best results. The summer maxima of precipitation, surface temperature and latent heat flux are simulated too early by about a month for several river catchment areas. This shift is strongest in the T106 and T159 models. Another problem with the annual cycle of precipitation is a relative minimum in August to October, especially in the low-resolution ECHAM5 models. The precipitation of the ECHAM5 simulations over the Arctic region exceeds all observational estimates by 5–15 mm/month, strongest in May–June. The latent heat flux over the river catchments has a clear trend towards increased fluxes with higher horizontal and vertical resolution, which seems to reach a maximum with T106. In the comparison of annual mean P-E (precipitation minus evaporation) with observed river discharge only the horizontal resolution seems to be important, again giving best results for the high-resolution models. The year-by-year variability of the simulations is too high, which is more pronounced for the higher-resolution versions. Especially strong impacts are found from the vertical resolution. The interannual variability of the latent heat flux is much smaller than that of precipitation and therefore the results shown for precipitation apply also for the simulated river discharge. Some forcing of ocean temperature anomalies on the precipitation over the Rhine, Kolyma and Indigirka catchment areas have been found, from the northeastern Atlantic and from the Pacific with developing El Niños. Despite the increased random variability in the higher-resolution models, the signal could be detected in almost all simulations. On the whole the higher-resolution (horizontal and vertical) ECHAM5 model simulations are quite improved compared to the low-resolution version of the same model and an older T42 model version. Increasing the vertical resolution from 19 to 31 levels is decisive for this better performance.
Influence of snow ablation and frozen ground on spring runoff generation in the Mogot Experimental Watershed, southern mountainous taiga of eastern Siberia
Authors: Suzuki Kazuyoshi , Kubota Jumpei , Ohata Tetsuo , Vuglinsky Valery
Published: May 2018

Snowmelt runoff is one of the most important discharge events in the southern mountainous taiga of eastern Siberia. The present study was conducted in order to understand the interannual variations in snowmelt infiltration into the frozen ground and in snowmelt runoff generation during the snowmelt period in the southern mountainous taiga in eastern Siberia. Analysis of the obtained data revealed the following: (1) snowmelt infiltration into the top 20 cm of frozen ground is important for evaluating snowmelt runoff generation because frozen ground absorbed from 22.9% (WY1983) to 61.5% (WY1981) of the maximum snow water equivalent. The difference in snowmelt infiltration for the two years appears to have been caused by the difference in snowmelt runoff generation; (2) the snowmelt runoff ratio increased with (i) increase in the fall soil moisture just before the soil surface froze and (ii) increase in the maximum snow water equivalent. The above results imply that the parameters governing snowmelt infiltration in the boreal taiga region in eastern Siberia are fall soil moisture and the maximum snow water equivalent, as is the case in the simple model presented by Gray et al.
Drinking water and diarrhoeal disease due to Escherichia coli
Authors: Hunter Paul R.
Published: May 2018

Escherichia coli has had a central place in water microbiology for decades as an indicator of faecal pollution. It is only relatively recently that the role of E. coli as pathogen, rather than indicator, in drinking water has begun to be stressed. Interest in the role of E. coli as a cause of diarrhoeal disease has increased because of the emergence of E. coli O157:H7 and other enterohaemorrhagic E. coli, due to the severity of the related disease. There are enterotoxigenic, enteropathogenic, enterohaemorrhagic, enteroinvasive, enteroaggregative and diffusely adherent strains of E. coli. Each type of E. coli causes diarrhoeal disease through different mechanisms and each causes a different clinical presentation. Several of the types cause diarrhoea by the elaboration of one or more toxins, others by some other form of direct damage to epithelial cells. This paper discusses each of these types in turn and also describes their epidemiology, with particular reference to whether they are waterborne or not.
Indigenous bacterial spores as indicators of Cryptosporidium inactivation using chlorine dioxide
Authors: Verhille Sophie , Hofmann Ron , Chauret Christian , Andrews Robert
Published: May 2018

This objective of this study was to explore the practicality of monitoring naturally occurring organisms to predict drinking water treatment plant performance, in this case for the reduction of Cryptosporidium. Surface and ground water from seven drinking water treatment plants across North America that use chlorine dioxide were surveyed for aerobic and anaerobic bacterial spore concentrations. The concentrations of total spores were usually high enough in both raw and treated water to allow 4- to 5-log reductions to be observed across the treatment train by filtering up to 2 l of sample. These results suggested that naturally occurring treatment-resistant spores could be candidates as indicators of treatment performance. However, to be useful as indicators for Cryptosporidium reduction, the organisms would have to exhibit similar resistances to disinfection (chlorine dioxide in this case) in order to be useful. The inactivation kinetics of seven of the most common species were determined, and all were observed to be considerably more susceptible to chlorine dioxide inactivation than Cryptosporidium as reported in the literature. This study therefore did not identify an appropriate ambient microbial indicator for Cryptosporidium control.
Application and refinement of the WHO risk framework for recreational waters in Sydney, Australia
Authors: Ashbolt N. J. , Bruno M.
Published: May 2018

Local adaptation of the World Health Organisation (WHO) Farnham approach to managing pathogen risk in recreational waters was readily achieved given the extensive microbiological beach data for Sydney, and a clear understanding of applying the ‘Annapolis Protocol’ sanitary survey component to beach classification. Daily enterococci counts were predicted by rainfall (>10 mm in 24 h or >5 mm over 4–5 days), or by wind direction/speed, sunlight and tide during dry periods. Quantitative microbial risk assessment models (maximum risk exponential model for gastroenteritis and adenovirus exponential model for respiratory illness) fitted the United Kingdom epidemiological data and show potential for use. Flexibility in interpreting what is important for local conditions is essential, illustrated by replacing the general descriptions in the Farnham report with more ridged values for stormwater-impacted beaches. Hence, a user-friendly format for bather risk management, based on key environmental predictors of faecal pollution (such as rainfall, wind direction and tide) should largely replace the need for regular and costly microbiological testing; providing risk estimates in real time and allowing immediate control measures, such as signage or temporary beach closures. Ongoing testing resources should be directed to understanding the source(s) of faecal contamination, comparing enterococci/enteric virus survival under warm Australian conditions and spot checks for recalibration of environmental factors.
Detection of human enteric viruses in stream water with RT-PCR and cell culture
Authors: Denis-Mize Kimberly , Fout G. Shay , Dahling Daniel R. , Francy Donna S.
Published: May 2018

A multiplex RT-PCR method was used to measure virus occurrence at five stream water sites that span a range of hydroclimatic, water-quality, and land-use characteristics. The performance of the molecular method was evaluated in comparison with traditional cell culture and Escherichia coli membrane filtration assays. The study incorporated multiple quality controls and included a control for virus recovery during the sampling procedure as well as controls to detect potentially false-negative and false-positive data. Poliovirus recovery ranged from 16 to 65% and was variable, even in samples collected within the same stream. All five sites were positive for viruses by both molecular and cell culture-based virus assays. Enteroviruses, reoviruses, rotaviruses, and hepatitis A viruses were detected, but the use of the quality controls proved critical for interpretation of the molecular data. All sites showed evidence of faecal contamination, and culturable viruses were detected in four samples that would have met the US Environmental Protection Agency's recommended E. coli guideline for safe recreational water.
Usefulness of monitoring tropical streams for male-specific RNA coliphages
Authors: Luther Kartini , Fujioka Roger
Published: May 2018

The objective of this study was to evaluate the usefulness of monitoring streams in Hawaii for FRNA coliphages as a reliable indicator of sewage contamination. This study was undertaken as a result of our previous findings that monitoring streams in Hawaii for traditional faecal indicator bacteria (faecal coliform, Escherichia coli, enterococci) was not useful in determining when streams are contaminated with sewage, because environmental (soil) sources rather than sewage accounted for the high concentrations of faecal bacteria in streams. Two perennial streams, sewage and soil samples were monitored for traditional faecal indicator bacteria (faecal coliform, E. coli, enterococci) and FRNA coliphages. The results showed that sewage treatment processes and disinfection drastically reduced the concentrations of traditional faecal indicator bacteria but FRNA coliphages were still present in significant concentrations in the treated sewage effluents. These results indicate that monitoring sewage effluents and environmental waters for only traditional faecal indicator bacteria may not be adequately protective of human health effects. Ambient concentrations of traditional faecal indicator bacteria in soil and streams of Hawaii were consistently high but consistently low for FRNA coliphages, indicating that monitoring streams of Hawaii for FRNA coliphages can be used to determine when streams are contaminated with sewage.
Assessment of drinking water quality using indicator bacteria and bacteriophages
Authors: Méndez Javier , Audicana Ana , Cancer Mercedes , Isern Anna , Llaneza Julian , Moreno Belén , Navarro Mercedes , Tarancón Ma Lluisa , Valero Fernando , Ribas Ferran , Jofre Juan , Lucena Francisco
Published: May 2018

Bacterial indicators and bacteriophages suggested as potential indicators of water quality were determined by public laboratories in water from springs, household water wells, and rural and metropolitan water supplies in north-eastern Spain. Indicator bacteria were detected more frequently than bacteriophages in springs, household water wells and rural water supplies. In contrast, positive bacteriophage detections were more numerous than those of bacteria in metropolitan water supplies. Most of the metropolitan water supply samples containing indicators had concentrations of chlorine below 0.1 mg l−1, their indicator loads resembling more closely those of rural water supplies than any other samples taken from metropolitan water supplies. The number of samples from metropolitan water supplies containing more than 0.1 mg l−1 of chlorine that contained phages clearly outnumbered those containing indicator bacteria. Some association was observed between rainfall and the presence of indicators. Sediments from service reservoirs and water from dead ends in the distribution network of one of the metropolitan water supplies were also tested. Bacterial indicators and phages were detected in a higher percentage than in samples of tap water from the same network. Additionally, indicator bacteria were detected more frequently than bacteriophages in sediments of service reservoirs and water from dead end samples. We conclude that naturally occurring indicator bacteria and bacteriophages respond differently to chlorination and behave differently in drinking water distribution networks. Moreover, this study has shown that testing for the three groups of phages in routine laboratories is easy to implement and feasible without the requirement for additional material resources for the laboratories.
Quantitative microbial risk assessment to estimate health risks attributable to water supply: Can the technique be applied in developing countries with limited data?
Authors: Howard Guy , Pedley Steve , Tibatemwa Sarah
Published: May 2018

In the 3rd edition of its Guidelines for Drinking-Water Quality (2004) (GDWQ) the World Health Organization (WHO) promotes the use of risk assessment coupled with risk management for the control of water safety in drinking water supplies. Quantitative microbial risk assessment (QMRA) provides a tool for estimating the disease-burden from pathogenic microorganisms in water using information about the distribution and occurrence of the pathogen or an appropriate surrogate. This information may then be used to inform decisions about appropriate management of the water supply system. Although QMRA has been used to estimate disease burden from water supplies in developed countries, the method has not been evaluated in developing countries where relevant data may be scarce. In this paper, we describe a simplified risk assessment procedure to calculate the disease burden from three reference pathogens – pathogenic Escherichia coli, Cryptosporidium parvum and rotavirus – in water supplies in Kampala, Uganda. The study shows how QMRA can be used in countries with limited data, and that the outcome can provide valuable information for the management of water supplies.
Detection of Salmonella spp. in water using magnetic capture hybridization combined with PCR or real-time PCR
Authors: Thompson D. E. , Rajal V. B. , De Batz S. , Wuertz S.
Published: May 2018

The removal of target DNA by magnetic capture hybridization (MCH) from constituents inhibitory to amplification by polymerase chain reaction (PCR) was evaluated using Salmonella as the test pathogen. Hybrids were subjected to both conventional and quantitative real-time PCR (qPCR). When PCR inhibitors commonly found in water were added to the reaction, MCH-PCR increased the detection sensitivity on the order of 8 to 2,000-fold compared with the system using only PCR. To determine the selectivity of MCH for target DNA (Salmonella), different amounts of non-target DNA (Escherichia coli) were added to the qPCR reaction. The highest non-target DNA concentration interfered with the amplification by qPCR alone, while MCH-qPCR was unaffected. Average recovery of Salmonella DNA by MCH-qPCR was 31% using optimized buffers, washing solutions and enzymatic digestion. A recovery function was proposed in order to calculate the real cell number based on the measured value. Preliminary testing confirmed the suitability of this method for analysis of natural waters.