ISSN:0885-6087    

DOI:10.1002/hyp.3360090802

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractA study was undertaken during the winter of 1990–1991 in a small (3.7 ha) Canadian Shield catchment to examine the hydrological and hydrochemical response during rain‐on‐snow events. The results are presented of two large (37.9 and 34.6 mm) rain‐on‐snow events occurring in early and late March 1991. Peak and total runoff and the groundwater response from the two events are significantly different. Hydrological data indicate that these differences can be attributed to a combination of meteorological (temperature) and physical conditions (antecedent snowpack ripeness, soil moisture and groundwater levels). An immature snowpack (low temperature and density) combined with low antecedent soil moisture conditions significantly reduced the magnitude of the net hydrological input and runoff from the catchment during the early March event, whereas a more mature snowpack and high antecedent soil moisture conditions led to a large runoff event during late March.During both rain‐on‐snow events a significant portion of the pre‐event snowpack chemical load was lost. Based on the maximum snowpack chemical load measured before the events, the two large rain‐on‐snow events and a brief mid‐March warm period during which there were two much smaller rain‐on‐snow events removed 78% of the hydrogen ion and 63% of the sulphate and nitrate load from the snowpack, while only reducing snowpack water equivalence by 7%. A two‐component (rain and snowmelt) isotopic (δ18O SMOW %0) separation of snowmelt lysimeter water during the two events indicated that snowmelt was an important (50 and 65%, respectively) water source available for infiltration and runoff at the snow‐soil interface. Considering the high hydrogen ion loadings to the catchment during these two events (3.3 and 3.0 mequiv.m−2, respectively) streamflow pH was not significantly reduced due to an increase in the discharge of well‐buffered groundwater. A two‐component isotopic hydrograph separation of peak stream discharge during the 2–3 March event indicated that 75% of the total flow was groundwater. In mid‐latitude acid‐sensitive catchments, winter rain‐on‐snow events are an important hydrological occurrence due to their ability to elute much of the chemical load (H+, SO4, NO3) from the snowpack before the onset of spring melt when the maxi

ISSN:0885-6087    

DOI:10.1002/hyp.3360090803

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractAn approach to spatially distribute a snow process model by segmenting images of land cover, terrain and snow properties is reported. A small 1.7 ha study area with an existing database was selected for this preliminary evaluation. The methodology was carried out over a relatively flat valley bottom at Camp Grayling, Michigan. Meteorological measurements on two sides of the area showed only small differences, so uniform meteorological variables were assumed over the site. Initial snow cover conditions were reconstructed and were distributed over the area using snow maps and sparse snow pit measurements. One metre resolution terrain, soil, vegetation and snow type maps were individually processed into class maps. These layers were then combined to produce a segmented class map, where the attributes from the data layers were known for each class. A one‐dimensional model of snow processes was run for each class, then the results were mapped back into images. Shallow snow conditions provided high sensitivity of ablation patterns to meteorological conditions over a 72 h period. The model performance was assessed by comparing predicted and observed ablation patterns. The error in total snow‐covered area was less than 9%. However, the location errors were greater (predicted snow where no snow was observed and observed snow where no snow was predicted). Extensive error analysis was not justified because of the lack of multiple point measurements of snow propert

ISSN:0885-6087    

DOI:10.1002/hyp.3360090804

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe Tretyakov non‐recording precipitation gauge has been used historically as the official precipitation measurement instrument in the Russian (formerly the USSR) climatic and hydrological station network and in a number of other European countries. From 1986 to 1993, the accuracy and performance of this gauge were evaluated during the WMO Solid Precipitation Measurement Intercomparison at 11 stations in Canada, the USA, Russia, Germany, Finland, Romania and Croatia. The double fence intercomparison reference (DFIR) was the reference standard used at all the Intercomparison stations in the Intercomparison. The Intercomparison data collected at the different sites are compatible with respect to the catch ratio (measured/DFIR) for the same gauge, when compared using mean wind speed at the height of the gauge orifice during the observation period.The Intercomparison data for the Tretyakov gauge were compiled from measurements made at these WMO intercomparison sites. These data represent a variety of climates, terrains and exposures. The effects of environmental factors, such as wind speed, wind direction, type of precipitation and temperature, on gauge catch ratios were investigated. Wind speed was found to be the most important factor determining the gauge catch and air temperature had a secondary effect when precipitation was classified into snow, mixed and rain. The results of the analysis of gauge catch ratio versus wind speed and temperature on a daily time step are presented for various types of precipitation. Independent checks of the correction equations against the DFIR have been conducted at those Intercomparison stations and a good agreement (difference less than 10%) has been obtained. The use of such adjustment procedures should significantly improve the accuracy and homogeneity of gauge‐measured precipitation data over large regions of the former USSR and central Eur

ISSN:0885-6087    

DOI:10.1002/hyp.3360090805

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractExperimental results are reported for dissolved solids concentration increase when clear meltwaters from the surface of an Alpine glacier were reacted with suspended sediment derived from the subsole. The experiments, at Findelengletscher, Switzerland, were conducted at temperatures of about 1°C. Rates of reaction, which decrease through time as solute content rises, were slower in meltwaters which had not been allowed to equilibrate with the atmosphere before sediment was added. Diurnal variations in transit times of meltwater from the surface to the glacier portal were derived from injections of rhodamine dye into large moulin‐conduit systems. Experimentally‐determined rates of increase of electrical conductivity were used together with observed transit times in a Lagrangian formulation. This model was used to assess the contributions of rate of reaction and flow‐through velocity to production of observed variations of solute concentration with portal meltwater discharge. The observed diurnal concentrations varied inversely but in phase with portal discharge. Diurnal variations in discharge through such moulin‐conduit systems lead to substantial changes in flow‐through velocity, altering the periods of time available for parcels of meltwater to react with basally‐entrained suspended sediment en route to the portal. Hence, there is considerable variability in the amount of solute acquired by meltwaters in transit. A diurnal pattern of solute concentration variation with discharge is generated by the model, although absolute levels of solute concentration are underestimated. Parcels of meltwaters flowing more slowly, having entered the glacier down small cracks, crevasses and tiny moulins, acquire larger concentrations of solute during longer transit times. These waters, which cumulatively account for a significant proportion of total discharge, mix with those traversing moulin‐conduit systems and presumably raise the overall solute content of the total discharge from Findelengletscher to the m

ISSN:0885-6087    

DOI:10.1002/hyp.3360090806

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractRunoff from a small glacierized catchment in the Canadian high Arctic was monitored throughout one melt season. The stream discharge record is one aspect of a larger project involving glacier mass balance, superimposed ice formation and local climate on a glacier in the Sawtooth Range, Ellesmere Island, Northwest Territories, Canada. To better understand the main factors influencing the production of runoff on the glacier during the period of main summer melt, regression analyses were performed relating daily air temperature, shortwave incoming and net radiation, absorptivity and wind speed to daily glacier discharge. Air temperature at the glacier meteorological station on rain‐free days is the element with the greatest correlation with runoff (r2= 0.57;n= 34). A multiple regression of discharge with air temperature, shortwave incoming radiation, net radiation hours and wind speed achieved the best fit (r2= 0.84;n= 34). Rain events (>10mmd−1) can dominate daily discharge when they occur during the period of ice melt, creating more runoff per unit area than can be produced by melt alone, and significantly reduce the accuracy of runoff predicti

ISSN:0885-6087    

DOI:10.1002/hyp.3360090807

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe influence of trees on the ground thermal regime is important to the overall winter energy exchange in a snow‐covered, forested watershed. In this work, spatial zones around a single conifer tree were defined and examined for their controls on the snow cover, snow‐ground interface temperatures and frozen ground extent. A large white spruce (Picea glauca), approximately 18 m tall with a crown diameter of 7.5 m and located in northern Vermont, was the subject of this study. The tree was instrumented with thermistors to measure the snow‐ground interface temperature between the tree trunk and 6 m from the tree into undisturbed snow. Four distinct zones around the conifer are defined that affect the snow distribution characteristics: adjacent to the trunk; the tree well; the tree crown perimeter; and the unaffected area away from the tree. At the time of peak snow accumulation and during the ablation season, snow depth and density profiles were measured. The area beneath the canopy accumulated 34% of the snow accumulated in the undisturbed zone. By the end of the ablation season, the depth of snow under the canopy had decreased to 18% of the undisturbed snow depth. The tree and branch characteristics of spruce in this temperate climate resulted in a different snow depth profile compared with previous empirical relationships around a single conifer. A new relationship is presented for snow distribution around conifer trees that has the ability to better fit data from a variety of conifer types than previously published relationships. Less snow beneath the canopy led to colder snow‐ground interface temperatures than measured in undisturbed snow. The depth of frozen ground in the different zones was modelled using a simple analytical solution that showed deeper frost penetration in the tree well than beneath the undisturb

ISSN:0885-6087    

DOI:10.1002/hyp.3360090808

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractFor successful snowdrift modelling, measured drift shapes should be geometrically similar to full‐scale shapes and develop at rates that scale in a known manner. Consensus exists on most modelling methods and the similitude requirements needed to meet these objectives. A notable exception is the manner to scale drift development rates. A rationale is presented for rate scaling based on an independent model and prototype mass transport measurements. This approach is validated by comparing the rate of drift development for a model Wyoming snow fence with corresponding field data. This method yields excellent agreement, whereas the alternatives differ substantiall

ISSN:0885-6087    

DOI:10.1002/hyp.3360090809

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe influence of winter on methane (CH4) stored in pore water and emitted through snow was investigated in a temperate poor fen in New Hampshire over two winters. Methane accumulated beneath ice layers (1 cm) deposited by freezing rain, resulting in snow‐pore air mixing ratios as high as 140 ppmv during the first winter and 600 ppmv during the second. An early winter snow crust of 300 kg m−3caused no discontinuity in a linear mixing ratio profile and therefore was not observed to retard snowpack emissions. Methane concentration‐depth profiles in pore water steepened and concentrations increased by as much as 400 μM at the 10 and 20 cm depths as the ice cover formed. This suggests that the peat‐ice cover plays an important part in CH4build‐up in pore water by limiting the transport of gases between the peat and the atmosphere. Pore water concentrations gradually declined through late winter. The seasonality of dissolved CH4in pore water over two winters and one summer showed an average annual amplitude of 1.3 gCH4m−2(25–75cm depth range), with a winter maximum of 4.7gCH4m−2. Emissions during the winter with average snowfall accounted for a larger percentage (9.2% in 1993–1994) of total annual emission than the winter with below‐average snowfall and warmer air temperature (2% in 1994–1995). Emissions averaged 56 and 26mg m−2day−1during the first and second winter (December, January a

ISSN:0885-6087    

DOI:10.1002/hyp.3360090810

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

ISSN:0885-6087    

DOI:10.1002/hyp.3360090801

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY