bluuebunny/crossref_metadata_2025 huggingface dataset:
Variability of Snowmelt Runoff and Soil Moisture Recharge
Authors: Harms T.E. , Chanasyk D. S.
Published: May 2018

The spatial and temporal variability of snowmelt runoff and soil moisture recharge within small watersheds must be quantified for use in distributed parameter snowmelt models. Snowmelt runoff, over-winter changes in soil moisture and soil temperatures were monitored over three annual snowmelt periods on two reclaimed watersheds in central Alberta, Canada. Slope aspect had a major influence on fall soil antecedent conditions and soil temperature. The south-facing slopes produced snowmelt the earliest, cleared of snow the soonest, yielded the least amount of runoff and had the greatest gain in over-winter soil moisture. Over-winter change in soil moisture was minimal when fall soil moisture levels were greater than 75% relative saturation. The power relationship between infiltration and snow-water equivalent of Granger et al. (1984) was not verified in this study, likely due to mid-winter melts that altered near-surface soil moisture and subsequently enhanced snowmelt runoff.
Snowpack Chemistry During Snow Accumulation and Melt in Mature Subalpine Forest and Regenerating Clear-Cut in the Southern Interior of B.C.
Authors: Hudson Robert O. , Golding Douglas L.
Published: May 2018

Chemical profiles in snowpacks were observed during snow accumulation and melt periods at subalpine sites in the southern interior of British Columbia. During accumulation periods, concentrations of nitrate, sulphate, chloride and sodium were higher than those of bulk snowfall in surface snowpack layers and lower in middle and basal layers. During melt periods, the opposite was true. This process of chemical profile reversals was found to repeat itself through successive cycles of melt and non-melt periods that typically occur at the site during the spring. This recurring cycle of chemical enrichment resulted in two distinct processes of ion elution. A “seasonal” process was observed in which there is an initial ion pulse followed by a slow exponential decline in concentration. An event based process consisting of ion pulses due to leaching of enriched surface layers was superimposed on the seasonal process. Forest cover type was found to exert an influence on snowpack chemistry during accumulation and melt. Significant differences between forest cover types were found among average chemical concentrations in enriched and depleted layers, suggesting that canopy density causes differences in chemical metamorphosis of snowpacks.
Energy and Water Balances of a Bog in Central Sweden
Authors: Phersson Mattias , Pettersson Ola
Published: May 2018

Fens and bogs represent a considerable part of the boreal forest area of Scandinavia, but have not received much attention. To understand their role in the water and energy balances an investigation was carried out during the spring and summer of 1994 as a part of the NOPEX program. Groundwater level, precipitation and energy budget parameters were measured at the Ryggmossen bog, 35 km Northwest of Uppsala. The evaporation (10 min averages) was determined by the Energy Balance Bowen Ratio method and a reference evaporation (10 min averages) was also calculated according to Penman (1948). The results of the evaporation and energy balance study showed that the actual evaporation was 60% of the reference evaporation and that the evaporation rate was dependent on the groundwater depth. The weather during the period was warm with extremely low precipitation. The evaporation therefore decreased during the summer in response to the increased depth to the groundwater table. A relation was found between the groundwater level recession rate and the evaporation rate. The albedo increased during the summer and any occasional decrease could be attributed to individual rain storms.
Correction of Daily Rain Gauge Measurements in the Baltic Sea Drainage Basin
Authors: Rubel Franz , Hantel Michael
Published: May 2018

Within the framework of BALTEX regular measurements made at about 4,200 rain gauge sites have been collected by the BALTEX Meteorological Data Centre. This network of rain gauges is about 10 times denser than the synoptic network; here it is used for the objective analysis of daily precipitation fields on the grids of the mesoscale models developed in the research project NEWBALTIC during the pilot period PIDCAP (August to October 1995). The observations were corrected for systematic measuring errors with the Dynamic Correction Model. Its main purpose is to correct for the wind-induced losses which is the largest error. The correction formulae use the synoptic observations of wind speed, temperature and rain intensity at the rain gauge station considered. For non-synoptic stations the values of the closest synoptic station are used as estimates; the mean distance of the synoptic stations within the drainage basin is 30 km. For evaporation and wetting losses, which represent the second largest error of the precipitation measurements, climatological corrections are applied. The formulae in the Dynamic Correction Model take instrument-specific properties into account; these comprise HELLMANN UNSHIELDED, SMHI SHIELDED, H&H-90 SHIELDED and TRETJAKOV SHIELDED. The spatial distribution of corrected precipitation values were objectively analysed according to Rubel (1998). They yield daily gridded precipitation fields over the drainage basin which are systematically higher than the uncorrected fields. The corresponding increase of the freshwater input into the Baltic Sea drainage basin is 4.7% in August, 5.8% in September and 9.1% in October 1995. Finally, the perspective for further developments and the generation of a ten-year data base of the BALTEX main intensive observational and modelling period BRIDGE is introduced.
Snow Cover Modelling as a Tool for Climate Change Assessment in a Swiss Alpine Catchment
Authors: Gellens D. , Barbieux K. , Schädler B. , Roulin E. , Aschwanden H. , Gellens-Meulenberghs F.
Published: May 2018

The daily step conceptual hydrological model IRMB (Integrated Runoff Model – Bultot) is further developed by the addition of a module designed to calculate the energy balance in high spatial resolution in a basin with very distinct relief and to simulate the surface related processes in a distributed way. The basin considered, the Landquart basin (area at the outlet Felsenbach: 616 km2, mean altitude 1,800 m a.s.l.), situated in the eastern part of the Swiss Alps, has been subdivided with GIS-methodology into 2,704 homogeneous units (altitude and aspect). Among all other water balance elements snow water equivalent is simulated for a period of 15 years. Climate scenarios for the 21st century from three climate change experiments are used in order to estimate the change in the distribution of the snow water equivalent in the basin. Finally, impacts on the potentiality of Alpine skiing activities in this region are discussed. It shows that the areas where profitability minimum requirements is reached from the point of view of snow amounts, are decreasing, because this limit would go up by about 250 m from 1,500 to 1,750 m a.s.l. for the 2020 scenario. Statistical tests indicate, however, that this change is still within the natural variability observed in the reference period 1981-1995.
Snow Wetness Influence on Impulse Radar Snow Surveys Theoretical and Laboratory Study
Authors: Lundberg A. , Thunehed H.
Published: May 2018

The snow-water equivalent of late-winter snowpack is of utmost importance for hydropower production in areas where a large proportion of the reservoir water emanates from snowmelt. Impulse radar can be used to estimate the snow-water equivalent of the snowpack and thus the expected snowmelt discharge. Impulse radar is now in operational use in some Scandinavian basins. With radar technology the radar wave propagation time in the snowpack is converted into snow-water equivalent with help of a parameter usually termed the a-value. Use of radar technology during late winter brings about risk for measurements on wet snow. The a-value for dry snow cannot be used directly for wet snow. We have found that a liquid-water content of 5% (by volume) reduces the a-value by approximately 20%. In this paper an equation, based on snow density and snow liquid water content, for calculation of wet-snow a-value is presented.
Ice Columns and Frozen Rills in a Warm Snowpack, Green Lakes Valley, Colorado, U.S.A.
Authors: Williams Mark W. , Rikkers Mark , Pfeffer W. Tad
Published: May 2018

Here we provide information on ice columns and frozen rills found in late-season snowpacks in and near the Green Lakes Valley of the Colorado Front Range, USA. The presence of ice columns and frozen rills in late season snowpacks may provide insights with which to understand the spatial distribution of preferential flowpaths in melting snowpacks. In July and August of 1996 and 1997 we found ice columns in every one of the more than 50 snow fields we investigated. The ice columns showed a consistent morphology; each column was approximately 75 cm in vertical extent, with about 5 cm projecting above the snow surface and 70 cm extending into the snowpack. An analysis of variance test shows that the 81 ice columns on the south-facing slopes were significantly greater than the 57 ice columns on the north-facing slope (p = 0.01). There were about 3 ice columns per square metre on the southfacing slopes and 2 ice columns per square metre on the north-facing slopes. There was an interesting hysteresis in snow and ice temperatures that became stronger with increasing depth in adjacent thermocouple arrays. This hysteresis in the temperature profiles is consistent with the release of latent heat from the freezing of greater amounts of liquid water in and near the ice columns compared to the surrounding snowpack. At the Martinelli catchment, spacing between the frozen rills averaged 2.6 m (n = 73). We interpret these “ribs” of solid ice to be the remnants of surface rills. Vertical ice columns were connected to these frozen rills. The ice columns and frozen rills may provide a snapshot or “schematic” diagram of the major flowpaths in a ripe and draining snowpack.
A Method Based on Taking the Average of Probabilities to Compute the Flow Duration Curve
Authors: Cigizoglu Hikmet Kerem
Published: May 2018

In this study a method based on taking the average of the probabilities is presented to obtain flow duration curve. In this method the exceedance probability for each flow value is computed repeatedly for all time periods within a year. The final representing exceedance is just simply the average of all these probabilities. The applicability of the method to daily mean flows is tested assuming various marginal probability distributions like normal, Pearson type III, log-Pearson type III, 2-parameter lognormal and 3-parameter lognormal distributions. It is seen that the observed flow duration curves were quite well approximated by the 2-parameter lognormal average of probabilities curves. In that case the method requires the computation of the daily mean and standard deviation values of the observed flow data. The method curve enables extrapolation of the available data providing the exceedance probabilities for the flows higher than the observed maximum flow. The method is applied to the missing data and ungauged site problems and the results are quite satisfactory.
Areal Precipitation and Temperature in the Swedish Mountains
Authors: Johansson Barbro
Published: May 2018

This paper presents an evaluation of three different methods for estimation of areal precipitation and temperature, with special emphasis on their applicability for runoff modelling in the Swedish mountains. All three methods estimate the areal values as a weighted mean of the observations at nearby meteorological stations. The weights are determined by:

1) a manual subjective selection of the most representative stations

3) inverse square distance weighting

4) optimal interpolation

The methods were tested in an area with complex topography and precipitation gradients. The evaluation included comparison of areal estimates, verification against point observations and the water balance equation, and sensitivity analyses with respect to method parameters and network changes.

The evaluation showed that for simple runoff modelling the subjective and optimal interpolation methods performed equally well, and considerably better than inverse-distance weighting. The evaluation also showed that none of the methods correctly described the spatial variation in precipitation and temperature in the investigated region. They are thus not directly applicable for non-routine modelling applications where the estimation of runoff is not the sole objective. All methods proved to be sensitive to the selection of parameter values, which pointed to possible improvements of the estimates. The optimal interpolation method seemed to be the least sensitive to changes in the meteorological network.
Hydrologic Investigations of Groundwater and Surface-water Interactions In Subarctic Alaska
Authors: Hinzman Larry D. , Wegner Matthew , Lilly Michael R.
Published: May 2018

Dynamic interactions between rivers and adjacent aquifers can significantly affect near-bank geochemistry and processes associated with natural attenuation of contaminants by mixing water or introducing oxygen or nutrients. During 1997 and 1998 in a study near Fairbanks, Alaska U.S.A, the hydrologic conditions in the Chena River and in the adjacent groundwater were monitored. The river stage, groundwater elevations, and the water chemistry and temperature in both river and groundwater were measured. In the spring of 1997, the groundwater gradient close to the Chena River reversed causing surface water to enter the aquifer. Changes in temperature, specific conductance and alkalinity were used to determine the extent of bank recharge. For approximately one week during spring snowmelt of 1997, surface-water influx from the Chena River occurred approximately between the depths of 5.33 m and 9.1 m below ground surface. The effects of bank recharge extended at least 6.1 m but not to 30.5 m from the banks of the Chena River into the aquifer. Bank recharge caused 64 to 68 per cent of the groundwater, 6.1 m from the bank at a depth of 6.78 m to be displaced by surface water influx. Peak flows during 1998 were not high enough to cause flow reversals.
Life in Glacial and Alpine Rivers in Central Iceland in Relation to Physical and Chemical Parameters
Authors: Gíslason Gísli Már , Ólafsson Jón S. , Adalsteinsson Hákon
Published: May 2018

The characteristics of stream and river ecosystems in arctic and alpine areas are determined mainly by the relative contribution of glacial meltwater, snowmelt, rainfall and groundwater. Each source generates a particular seasonal hydrological signature, affecting physical and chemical properties, and hence biological communities. The relative contribution of each source is sensitive to climate change. The study was concentrated on the glacial River W-Jökulsá and some non-glacial rivers in the central highlands of Iceland. The water in the glacial river was entirely glacial meltwater at the glacier margin, but the glacial contribution was about 20% 40 km downstream. However, its tributaries and non-glacial reference rivers were mainly springfed. The invertebrate fauna was confined to Chironomidae of the genus Diamesa close to the glacier, but other taxa (species and groups of species) occupied the river further downstream, where their diversity was close to that found in the reference rivers.
Snow Distribution at a High Arctic Site at Svalbard
Authors: Bruland Oddbjørn , Sand Knut , Killingtveit Ånund
Published: May 2018

In the Arctic regions snow cover has a major influence on the environment both in a hydrological and ecological context. Due to strong winds and open terrain the snow is heavily redistributed and the snow depth is quite variable. This has a significant influence on the duration of the melting season, on the possibilities of greenhouse gas exchange, the plant growing season and therefore the arctic terrestrial fauna. The aim of this study is to describe the snow depth variability by detailed measurement of snow distribution in a 3 km2 site near to Ny-Ålesund at 79° north of Svalbard and to link this to topography and climate at the location. The measurements were carried out in a grid of 100 m by 100 m cells using the SIR-2 Georadar from Geophysical Survey System Inc. (GSSI).

Differential GPS was used to create a detailed Digital Elevation Model (DEM) and the snow depth data were correlated to topographic data. The average snowdepth in the area was about 70 cm with a standard deviation of 40 cm. Statistical distribution and spatial correlation for the snow depths were found. The method was found acceptable for snow distribution mapping. The main observation was the major accumulation in the west facing slopes due to easterly winds that are dominant in this area.
Internal HBV-96 Variables and Phosphorus Transport Processes
Authors: Lidén Rikard
Published: May 2018

The high data requirements of total phosphorus (TP) transport prediction tools limit their application. Recently, research has therefore started in Sweden to use a conceptual hydrological model, HBV-96, as a base for TP estimation. A first step is, however, to understand the relationship between model variables and natural processes. A review of particulate and dissolved material transport enabled the most important TP transport processes to be found for small Swedish catchments. A probabilistic flow categorisation technique based on the internal HBV-96 variables is suggested. Days with a high probability of saturated overland flow are identified with an overland flow index based on the water content of the upper response box and rainfall/melt rates. Further categorisation into intermediate and base flow is done on the basis of water contents in the lower and upper response boxes of the model. The flow categorisation technique was tested in a catchment with TP and suspended sediment records. The results show significantly different concentration distributions and median values between the flow categories. The HBV-96 internal variables, in general, are more highly correlated to concentration than is observed river runoff and it may thus be beneficial to apply the model to assess TP transport compared to using observed runoff directly. Model parameter interdependence is highlighted as a shortfall in the general use of HBV-96 for flow categorisation.
Interannual and Seasonal Temperature and Salinity Variations in the Gulf of Riga and Corresponding Saline Water Inflow From the Baltic Proper
Authors: Raudsepp Urmas
Published: May 2018

Salinity and temperature data from the Gulf of Riga, a semi-enclosed sub-basin of the Baltic Sea, were analyzed with a focus on interannual and seasonal variability. The data were compiled from measurements taken from 1973 to 1995, a period which includes the stagnation period in the Baltic Sea. Interannual and seasonal variations in the net inflow of saline water from the Baltic Proper were estimated from volume and salt conservation equations for the period 1973-90.

The basic decreasing trend, superimposed interannual variations in salinity, and interannual and seasonal temperature variations in the Gulf of Riga coincided with corresponding changes above the halocline in the Baltic Proper. Seasonal salinity variations were notable in the Gulf of Riga as compared to the Baltic Proper, where variations were negligible. Estimated annual mean inflow varied between 2,000 and 5,000 m3/s (average 3,200 m3/s), with a notable increasing trend. A simultaneous increasing trend was extracted from annual mean river flow data. Short-term fluctuations (over 4-6 years) of annual mean inflow ran opposite to the fluctuations of the magnitude of river flow. The average salinity in the Gulf of Riga increased during strong inflow and weak river flow and decreased when inflow was weak and river flow was strong. Variations in the inflow of water salinity had a minor effect on salinity variations in the Gulf of Riga. Seasonal inflow was strongest in spring and autumn and weak in winter.
Comparison of Modeled Water Input and Measured Discharge Prior to a Release Event: Unteraargletscher, Bernese Alps, Switzerland
Authors: Schuler Thomas , Fischer Urs H. , Sterr Regina , Hock Regine , Gudmundsson G. Hilmar
Published: May 2018

A distributed temperature index melt model including potential clear-sky solar radiation was applied to Unteraargletscher, Bernese Alps, Switzerland, to quantify water input to the glacial hydrological system during the ablation season 1999. Model parameters were determined by calibrating calculated melt with ablation measurements. Discharge was measured in the proglacial stream for 18 days until the station was destroyed by an outburst flood.

Comparison of modeled melt and measured discharge reveals that routing processes of water through the glacier vary with time as the water is transferred through a dynamic drainage system. Furthermore, an imbalance of water input and output suggests that water was stored in or beneath the glacier during this period. The culminating outburst flood presumably released this en– or subglacially stored water and may be related to a change in the configuration of the glacial drainage system as inferred from measurements of subglacial water pressure.
Influence of Sub-Debris Thawing on Ablation and Runoff of the Djankuat Glacier in the Caucasus
Authors: Popovnin Victor V. , Rozova Anastassia V.
Published: May 2018

Superficial moraines grew in size during the entire 32-year-long period of direct monitoring of water and ice balance of the Djankuat Glacier in the Caucasus. The total area of debris cover on the glacier increased from 0.104 km2 (3% of the entire glacier surface) in 1968 to 0.266 km2 (8% of the glacier) in 1996. Such rapid dynamics of moraine formation greatly influences the ablation rate and distorts fields of mass-balance components. Sub-debris thawing can be calculated by means of a model, which describes the role of debris cover for the thermal properties of a glacier. Its meltwater equivalent depends mainly on debris thickness. In 1983 and 1994 the debris cover was repeatedly mapped over the whole glacier portion that was covered with morainic material. Sub-moraine ablation increases (vs. pure ice surface) under the thin, less than ca. 7-8 cm, debris layer, whereas the thicker debris cover reduces the liquid runoff due to its shielding effect. Zones differing due to their hydrological effect are depicted on the glacier map and the degree of debris influence on ablation is estimated quantitatively. As a whole runoff from debris-covered parts of the Djankuat Glacier has diminished due to the dominant shielding effect. Variation of the terminus is also shown to be dependent on the evolution of superficial moraine.
Indirect Estimation of the Djankuat Glacier Volume Based on Surface Topography
Authors: Aleynikov A. A. , Popovnin V. V. , Voytkovskiy K. F. , Zolotaryov Ye. A.
Published: May 2018

The relationship between the thickness of a glacier stream and its surface slope is discussed. Morphometrical features of the glacier surface serve as a basis for estimating the maximum thickness the glacier can attain. A method for indirect calculation of ice thickness is hereby suggested. A detailed large-scale map permits determination of the total glacier volume. The Djankuat Glacier, a representative valley glacier in the Central Caucasus, is used as an example to illustrate the applicability of the proposed calculation scheme. Its probable thickness and volume are estimated on the grounds of photogrammetrical surveys, a topographic map and spatial pattern of ice flow velocity on the surface. Several values of directly measured ice thickness (by various methods such as thermal drilling, radar sounding, gravimetry etc.) verify the calculation results. As a result, ice thickness over the entire glacier area has been mapped. Methodical limitations and accuracy of indirect estimates are also discussed.
Seasonal Mixing and Genesis of Endogenic Meromixis in Small Lakes in Southeast Norway
Authors: Hongve Dag
Published: May 2018

The inland region of Southeast Norway contains many lakes with endogenic meromixis. A synoptic study of seasonal mixing was conducted in 27 oligo- and mesotrophic lakes with surface area 0.0013 – 7.4 km2 and water colour 2-146 Hazen units. The scope was to identify properties of morphometric, optical and chemical nature that lead to development of endogenic meromixis. The summer mixing depths were found to depend on lake area and water colour. Small lakes (< 0.3 km2) were incompletely aerated during the spring circulation and had hypolimnetic temperatures near the temperature of maximum density throughout the summer stagnation. Insubstantial autumn mixing is considered the primary reason lakes in this area develop meromixis. Iron and manganese concentrations in anoxic deep waters depend on concentrations in the sediments and on accumulation of dissolved inorganic carbon in the deep waters. Development of endogenic meromixis is favoured by iron concentration in the sediment more than 5% of dry weight and manganese more than 0.5% of dry weight.
Improving Runoff Simulations using Satellite-observed Time-series of Snow Covered Area
Authors: Engeset R.V. , Udnæs H-C. , Guneriussen T. , Koren H. , Malnes E. , Solberg R. , Alfnes E.
Published: May 2018

Snowmelt can be a significant contributor to major floods, and hence updated snow information is very important to flood forecasting services. This study assesses whether operational runoff simulations could be improved by applying satellite-derived snow covered area (SCA) from both optical and radar sensors. Currently the HBV model is used for runoff forecasting in Norway, and satellite-observed SCA is used qualitatively but not directly in the model. Three catchments in southern Norway are studied using data from 1995 to 2002. The results show that satellite-observed SCA can be used to detect when the models do not simulate the snow reservoir correctly. Detecting errors early in the snowmelt season will help the forecasting services to update and correct the models before possible damaging floods. The method requires model calibration against SCA as well as runoff. Time-series from the satellite sensors NOAA AVHRR and ERS SAR are used. Of these, AVHRR shows good correlation with the simulated SCA, and SAR less so. Comparison of simultaneous data from AVHRR, SAR and Landsat ETM+ for May 2000 shows good inter-correlation. Of a total satellite-observed area of 1,088 km2, AVHRR observed a SCA of 823 km2 and SAR 720 km2, as compared to 889 km2 using ETM+.
The Correlation Between Extreme Wind and Flood Events in Unregulated River Basins
Authors: Harstveit Knut , Jenssen Lars
Published: May 2018

The aim of this investigation is to improve the method for calculating design wind speed used for wave run up at water reservoirs. It is focused on the relation between extreme flood and wind events, and between wind speed and duration.

Water flow data from fourteen Norwegian river basins and wind data from neighbouring airfields are correlated. Some positive correlation is found for areas situated at the coastal side of the mountains where a further analysis is carried out. Extreme value analysis of the wind and flood series provides estimates of T-year events for each of the two variables. The best-fitted equation linking the square of the maximum 10-minute wind speeds to the daily mean water flow is established. It is observed that the expected wind speed during the 1000-year daily flood event has approximately one year return period. The risk for higher wind speed is high, so the effect of adding 1 and 1.65 standard deviations of the maximum wind speed is assessed, increasing the expected return period to 5 and 20 years respectively.

Continuous records of 10-minute wind speed are used to establish transfer coefficients from the extreme 10-minute value to durations of 20 minutes to 6 hours.
Modelling Erosion and Deposition of Cohesive Sediments from Hay River, Northwest Territories, Canada
Authors: Milburn David , Krishnappan B.G.
Published: May 2018

A large volume sample of river-bed cohesive sediment and water from Hay River, Northwest Territories, Canada was collected during a spring field program in 2000 as part of a study on under-ice movement of sediment just before breakup. Controlled laboratory experiments were subsequently conducted on the Hay River water/sediments in a rotating annular flume at Burlington, Ontario, Canada to better understand the deposition and erosion processes of cohesive sediment transport. The deposition experiments in the rotating flume confirmed that the Hay River sediment is cohesive and the critical shear stress for deposition and the rates of deposition are a function of bed shear stress and the initial concentration of the sediment in suspension. The erosion experiments provided quantitative data on the critical shear stress for erosion and the rates of erosion as a function of bed shear stress and the age of the sediment deposit. The erosion experiments also indicated that the growth of the biofilm had an influence on the erosion characteristics of the Hay River sediment. Based on the data from the rotating circular flume experiments, a modelling strategy is proposed for calculating the under-ice transport of the cohesive sediments in the Hay River.
Wavelet analysis for modeling suspended sediment discharge
Authors: Aksoy Hafzullah , Akar Tanju , Ünal N. Erdem
Published: May 2018

Wavelets, functions with zero mean and finite variance, have recently been found to be appropriate tools in investigating geophysical, hydrological, meteorological, and environmental processes. In this study, a wavelet-based modeling technique is presented for suspended sediment discharge time series. The model generates synthetic series statistically similar to the observed data. In the model in which the Haar wavelet is used, the available data are decomposed into detail functions. By choosing randomly from among the detail functions, synthetic suspended sediment discharge series are composed. Results are compared with those obtained from a moving-average process fitted to the data set.
The role of winter sublimation in the Arctic moisture budget
Authors: Liston G.E. , Sturm M.
Published: May 2018

In the Arctic, the simplest way to describe the winter surface moisture budget (in the absence of any net horizontal transport) is: snow-water-equivalent depth on the ground (D) equals precipitation (P) minus sublimation (S). D, P and S are the most fundamental components of the winter arctic hydrologic cycle and understanding them is essential to understanding arctic moisture-related processes. Unfortunately, accurate solid-precipitation (P) measurements have proven nearly impossible to achieve in the Arctic, because precipitation generally falls when it is windy. Gauge undercatch can range from 55–75% depending on the gauge type and wind conditions. The state of knowledge for winter sublimation (S) is even more limited. There are few actual measurements and most studies have used physical models to estimate this quantity. Moreover, fundamental questions concerning the boundary-layer physics of arctic winter sublimation remain unanswered. Resolving these is essential to closing local, regional, and pan-Arctic moisture budgets because some studies indicate sublimation may be as much as 50% of the total winter precipitation and 35% of the annual precipitation. This paper summarizes and analyzes the existing literature describing arctic sublimation.
Intensity and spatio-temporal variability of chemical denudation in an arctic-oceanic periglacial drainage basin in northernmost Swedish Lapland
Authors: Beylich Achim A.
Published: May 2018

The intensity and spatio-temporal variability of chemical denudation was analyzed in the Latnjavagge drainage basin (9 km2; 950–1440 m a.s.l.; 68°20′N, 18°30′E), an arctic–oceanic periglacial environment in northernmost Swedish Lapland. Data on daily runoff and solute concentrations at different test sites within the selected representative drainage basin were collected during the entire arctic summer seasons of 2000, 2001, 2002 and 2003. The mean annual chemical denudation net rate for the Latnjavagge drainage basin is 5.4 t/km2 yr. Most of the annual runoff occurs when the ground is still frozen. The rate in Latnjavagge is much lower than chemical denudation rates reported for Kärkevagge (Swedish Lapland) situated close to Latnjavagge, but at a similar level to a number of other subarctic, arctic and alpine environments. Chemical denudation shows a spatio-temporal variability within the drainage basin, which is mainly caused by a spatio-temporal variability of snow cover and ground frost and a spatial variability of regolith thicknesses within Latnjavagge.
Hydrological function of a thin extensive green roof in southern Sweden
Authors: Bengtsson Lars , Grahn Lennart , Olsson Jonas
Published: May 2018

The runoff from and the water balance of a thin extensive green roof with sedum-moss have been studied. The soil cover is about 3 cm underlain by a thin drainage layer. The water balance is determined on a monthly basis. The runoff from the green roof is much reduced compared to runoff from hard roofs because of evapotranspiration. The annual runoff is rather close to that of natural river basins. Although most rainy days there is no or little runoff from the roof, the highest observed daily runoff values are close to the daily rainfall. Runoff is initiated when the soil is at field capacity, which for the studied roof corresponds to 9 mm storage. After that, on a not very short time basis, the runoff equals the precipitation. The reduction of the daily runoff can be described in a simple way knowing the daily precipitation, potential evaporation and storage capacity of the green roof.
Peak flows from thin sedum-moss roof
Authors: Bengtsson L.
Published: May 2018

The runoff from real 3 cm thick sedum-moss roofs and from laboratory roof plots in southern Sweden is measured and analysed. Real rains and artificial storms are used for the analysis. The probability of high runoff is compared with the probability of high precipitation intensity. Intensity–duration–frequency curves for runoff are derived and it is found that the runoff of 1.5 year return period corresponds to rain of 0.4 year return period. The storage of water in the soil–vegetation cover on the roof is determined. The storage at field capacity, when runoff is initiated, is about 9 mm. Water in excess of that is temporary stored during storms. The runoff distribution during prolonged storms can be related to the mean rain intensity over 20–30 min. The influence of the slope and length of the roof on the runoff peak is investigated as is the effect of the drainage layer. Neither slope nor length seems to significantly influence the runoff distribution, which indicates that the vertical percolation process through the vegetation and the soil dominates the rainfall–runoff process. The presence of a drainage layer below the soil results in somewhat faster runoff compared to when there is no drainage layer, and thus results in an increased runoff peak.
Long-term changes in the frequency of cyclones and their trajectories in Central and Northern Europe
Authors: Sepp Mait , Post Piia , Jaagus Jaak
Published: May 2018

Changes in the number of cyclones and cyclone trajectories in Central and Northern Europe during 1948–2000 are analysed using a database of cyclones. Two hypotheses are advanced. Firstly, the number of cyclones reaching Northern Europe has increased, causing a transition to a more maritime climate. Secondly, the trajectories of cyclones have moved northward, causing the advection of warm and moist air to Northern Europe and decreasing precipitation in Central Europe. These advances were confirmed by data analysis. A linear trend and its statistical significance (P<0.05) for the frequency of cyclones in the Atlantic–European sector (30°W–45°E, 35–75°N) were calculated. Circles with radii of 500, 1000, 1500 and 2000 km with centre coordinates 60°N and 22.5°E were generated. All the cyclones whose centres were located within these circles were counted. Also two meridians −5°E and 20°E – were selected and all the cyclones were counted whose centres crossed the meridians from west to east in the interval of 45–75°N. Changes in the frequency of long-term cyclones were analysed. The number of cyclones reaching Northern Europe has increased in the period 1948–2000. The number of cyclones over the Baltic Sea has increased, especially in the winter. In Central Europe, the number of cyclones has decreased, especially in the warm half-year. The number of long cyclones has increased over the Baltic Sea, especially in the cold half-year.
A comparison between the ERA40 and the SMHI gridded meteorological databases as applied to Baltic Sea modelling
Authors: Omstedt A. , Chen Y. , Wesslander K.
Published: May 2018

Two gridded meteorological data sets for the Baltic Sea region, both having 1°×1° horizontal resolution, were compared and analysed for use in Baltic Sea modelling. The SMHI 1°×1° data set covers surface parameters with a three-hour time resolution over the 1970–2004 period. The ERA40 data cover analysed and modelled parameters for several atmospheric layers with a six-hour time resolution over the 1957–2002 period. Meteorological variables considered in this analysis were air temperature, wind speed, total cloud cover, relative humidity and precipitation. In considering Baltic Sea modelling, we examined maximum ice extent, water temperature, salinity and net precipitation calculations.

The two data sets are largely similar and can both be used in Baltic Sea modelling. However, their horizontal resolution is too coarse for resolving marine conditions over the Baltic Sea. This implies, for example, that the ERA40 original surface winds are too low for some Baltic Sea regions. The ERA40 precipitation values are also too low compared with those of the SMHI and other available data.
Simulation of temperature influence on flow pattern and residence time in a detention tank
Authors: Adamsson Åsa , Bergdahl Lars
Published: May 2018

Three-dimensional simulations were used to model how a temperature difference between the incoming water and tank water influences the flow pattern and residence time in a detention tank. Buoyant, neutrally buoyant and negatively buoyant incoming jets were simulated. The simulations were compared with measurements for neutrally buoyant jets in a large-scale model of a detention tank (13 × 9×1 m). The results show that a negatively buoyant jet gives slightly less effective volume, defined as the time when 50% of added tracer has passed the outlet divided by the nominal residence time, than a neutrally buoyant jet. The flow pattern for a negatively buoyant jet at low densimetric Froude numbers consists of a current that travels along the bottom towards the outlet and a counter current at the surface towards the inlet, while the neutrally buoyant jet excites a surface jet with two large eddies on each side of the jet. This implies that the short-circuiting will decrease when a negatively buoyant jet at low densimetric Froude number occurs in the tank. The difference between the flow pattern excited by a buoyant jet and a neutrally buoyant jet is small.
Long-term modelling of winter ice periods for morphologically different lakes
Authors: Elo Aija-Riitta
Published: May 2018

Winter ice cover can be related to the temperature of air, but morphological and meteorological differences cause large variations. Physically based modelling help their study, as results can be controlled and verified. A lot of data is needed, and in the process liability and interpretation of data are important. In this study long series of data are used to study winter ice coverage of morphologically different lakes in Southern Finland. Physical factors in the vertically resolving lake model, the Probe model, were considered. The ice model is based on the use of the temperature of air and it is successful in describing regular ice formation and break-up. Suitability for individual lakes could be improved by changing the factors for melting, the wind limit for breaking the ice and the temperature limit for determining ice coverage. Depth delays and mixing increases cooling of water. For freezing date, the differences between lakes are about one month. Ice break-up is strongly determined by air temperature, but the model can help to relate differences to morphology. During warmer winters horizontal variations have more importance; there can also be periods of partial ice-cover. For further study of those the model should be developed; modelling over years in succession is then a necessity.
A novel technology to improve drinking water quality: a microbiological evaluation of in-home flocculation and chlorination in rural Guatemala
Authors: Rangel Josefa M. , Lopez Beatriz , Mejia Maricruz Alvarez , Mendoza Carlos , Luby Stephen
Published: May 2018

An estimated 1 billion persons in low-income countries do not have access to improved drinking water. Chlorine, a useful water treatment agent, is less effective in turbid water, and lacks a visible effect, limiting its acceptability. A product incorporating precipitation, coagulation, flocculation, and chlorination technology (combined product) to reduce microbial, organic and heavy metal contaminants in water was evaluated. The combined product's microbiological efficacy in Guatemalan villagers' households was evaluated. One hundred randomly selected households from four neighboring Guatemalan villages were enrolled. Three groups received the combined product and either the Centers for Disease Control (CDC) water storage vessel, a covered bucket with spigot, or no vessel. One group received chlorine bleach and the CDC water storage vessel, and one group no intervention. Household water samples were collected for 4 weeks and Escherichia coli, chlorine, and turbidity levels were measured. Potable water was defined as having less than one E. coli per 100 ml. Eight (8%) baseline water samples were potable. Follow-up water samples were more likely to be potable than control samples (combined product and traditional vessel 83%; combined product and CDC vessel 92%; combined product and covered bucket with spigot 93%; chlorine and CDC vessel 92%; versus control 5%). Among combined product users, 98% reported improved water clarity compared with 45% of chlorine bleach users (p<0.0001). The combined product technology improved water potability as effectively as chlorine bleach; improved water clarity could motivate more persons to effectively treat their water.
Fate of effluent organic matter during soil aquifer treatment: biodegradability, chlorine reactivity and genotoxicity
Authors: Quanrud David M. , Arnold Robert G. , Lansey Kevin E. , Begay Carmen , Ela Wendell , Gandolfi A. Jay
Published: May 2018

Hydrophobic acid (HPO-A) and transphilic acid (TPI-A) fractions of dissolved organic matter (DOM) were isolated from a domestic secondary wastewater effluent that was polished via soil aquifer treatment (SAT). Fractions were isolated using XAD resin adsorption chromatography from samples obtained along the vadose zone flowpath at a full-scale basin recharge facility in Tucson, Arizona. Changes in isolate character during SAT were established via biodegradability (batch test), specific ultraviolet light absorbance (SUVA), trihalomethane formation potential (THMFP), and Ames mutagenicity assays. The dissolved organic carbon (DOC) concentration decreased by >90% during SAT. A significant fraction (up to 20%) of isolated post-SAT HPO-A was biodegradable. The (apparent) refractory nature of DOM that survives SAT may be a consequence of low DOC concentration in groundwater as well as the nature of the compounds themselves. Specific THMFP (µg THM per mg DOC) of HPO-A and TPI-A varied little as a consequence of SAT, averaging 52 and 49 µg THM per mg DOC, respectively. The nonbiodegradable fractions of HPO-A and TPI-A exhibited higher reactivities: 89 and 95 µg THM per mg DOC, respectively. Genotoxicity of HPO-A (on a per mass basis) increased after SAT, suggesting that responsible compounds are removed less efficiently than bulk organics during vadose zone transport.
Faecal contamination of drinking water during collection and household storage: the need to extend protection to the point of use
Authors: Clasen Thomas F. , Bastable Andrew
Published: May 2018

Paired water samples were collected and analysed for thermotolerant coliforms (TTC) from 20 sources (17 developed or rehabilitated by Oxfam and 3 others) and from the stored household water supplies of 100 households (5 from each source) in 13 towns and villages in the Kailahun District of Sierra Leone. In addition, the female head of the 85 households drawing water from Oxfam improved sources was interviewed and information recorded on demographics, hygiene instruction and practices, sanitation facilities and water collection and storage practices. At the non-improved sources, the arithmetic mean TTC load was 407/100 ml at the point of distribution, rising to a mean count of 882/100 ml at the household level. Water from the improved sources met WHO guidelines, with no faecal contamination. At the household level, however, even this safe water was subject to frequent and extensive faecal contamination; 92.9% of stored household samples contained some level of TTC, 76.5% contained more than the 10 TTC per 100 ml threshold set by the Sphere Project for emergency conditions. The arithmetic mean TTC count for all samples from the sampled households was 244 TTC per 100 ml (geometric mean was 77). These results are consistent with other studies that demonstrate substantial levels of faecal contamination of even safe water during collection, storage and access in the home. They point to the need to extend drinking water quality beyond the point of distribution to the point of consumption. The options for such extended protection, including improved collection and storage methods and household-based water treatment, are discussed.
Recommendations for microbial source tracking: Lessons from a methods comparison study
Authors: Stewart Jill R. , Ellender R. D. , Gooch Janet A. , Jiang Sunny , Myoda Samuel P. , Weisberg Stephen B.
Published: May 2018

The methods comparison study described in accompanying manuscripts demonstrated the potential value of microbial source tracking (MST) techniques, but also identified a need for method refinement. This paper provides three classes of recommendations to improve MST technology: optimization, development and evaluation. Optimization recommendations focus on library-dependent methods and include improved selection of restriction enzymes or antibiotics, better definition of appropriate library size, selection of target species and choice of statistical pattern-matching algorithms. Methods development recommendations focus on identifying new genomic targets and quantification procedures for library-independent methods. Longer-term methods development recommendations include integration of microarrays and other direct pathogen detection technology with MST. Studies defining host specificity and population dynamics should aid selection of target species during methods development. Evaluation recommendations include enhancements that should be incorporated into future methods comparison studies, along with studies to assess the value of MST results for risk characterization.