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  • 1
    In: Canadian Journal of Forest Research (Revue canadienne de recherche forestière), 2010, Vol.40(4), pp.812-821
    Description: The current mountain pine beetle infestation in British Columbias lodgepole pine forests has raised concerns about potential impacts on water resources. Changes in forest structure resulting from defoliation, windthrow, and salvage harvesting may increase snow accumulation and ablation (i.e., spring runoff and flooding risk) below the forest canopy because of reduced snow interception and higher levels of radiation reaching the surface. Quantifying these effects requires a better understanding of the link between forest structure and snow processes. Light detection and ranging (lidar) is an innovative technology capable of estimating forest structure metrics in a detailed, three-dimensional approach not easily obtained from manual measurements. While a number of previous studies have shown that increased snow accumulation and ablation occur as forest cover decreases, the potential improvement of these relationships based on lidar metrics has not been quantified. We investigated the correlation between lidar-derived and ground-based traditional canopy metrics with snow accumulation and ablation indicators, demonstrating that a lidar-derived forest cover parameter was the strongest predictor of peak snow accumulation ( r 2 = 0.70, p 〈 0.001) and maximum snow ablation rate ( r 2 = 0.59, p 〈 0.01). Improving our ability to quantify changes in forest structure in extensive areas will assist in developing more robust models of watershed processes.
    Description: Linfestation actuelle du dendroctone du pin ponderosa dans les forts de pin tordu de la Colombie-Britannique a suscit des inquitudes quant aux impacts potentiels sur les ressources hydriques. Les changements dans la structure de la fort causs par la dfoliation, les chablis et les coupes de rcupration pourraient augmenter laccumulation de neige et lablation nivale (c.--d. le ruissellement printanier et le risque dinondation) sous le couvert forestier en rduisant linterception et en augmentant le rayonnement au sol. La quantification de ces effets exige une meilleure comprhension du lien entre la structure de la fort et les processus nivaux. La dtection et tlmtrie par ondes lumineuses (lidar) est une technologie innovatrice capable destimer les mtriques de la structure de la fort avec une approche tridimensionnelle dtaille, difficile obtenir laide de mesures prises manuellement. Bien que plusieurs tudes prcdentes aient montr que laccumulation de neige et lablation nivale augmentent mesure que le couvert forestier diminue, lamlioration potentielle de ces relations au moyen de donnes lidar na pas t quantifie. Nous avons tudi la corrlation entre les mesures du couvert drives du lidar et les mesures traditionnelles prises au sol avec des indicateurs daccumulation de neige et dablation nivale. Nous avons dmontr quun paramtre du couvert forestier driv du lidar est le meilleure prdicteur de laccumulation maximale de neige ( r 2 = 0,70, p 〈 0,001) et du taux maximum dablation nivale ( r 2 = 0,59, p 〈 0,01). Lamlioration de notre capacit quantifier les changements dans la structure de la fort sur de vastes tendues contribuera dvelopper des modles plus robustes des processus dans les bassins versants.
    Keywords: Forest Management -- Methods ; Tree Crops -- Distribution;
    ISSN: 0045-5067
    E-ISSN: 1208-6037
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  • 2
    Language: English
    In: Journal of Hydrology, 2011, Vol.396(3), pp.277-291
    Description: ► Specification of spatially distributed lateral fluxes affects solute transport parameter estimates. ► Information contained on the breakthrough curve alone is insufficient to select the appropriate model structure. ► Implementation of , the lateral ouflow, in OTIS leads to solute mass to groundwater. ► The absence of implementation of in OTIS promotes the storage of solute mass in the transient storage zone. Interactions between mobile stream water and transient storage zones have been the subject of careful attention for decades. However, few studies have considered explicitly the influence of water exchange between the channel and neighbouring hydrological units when modelling transient storage processes, especially the lateral inflow coming from hillslope contributions and outflow to a deep aquifer or to hyporheic flow paths extending beyond the study reach. The objective of this study was to explore the influence of different conceptualizations of these hydrologic exchanges on the estimation of transient storage parameters. Slug injections of sodium chloride (NaCl) were carried out in eight contiguous reaches in the Cotton Creek Experimental Watershed (CCEW), located in south-east British Columbia. Resulting breakthrough curves were subsequently analysed using a Transient Storage Model (TSM) in an inverse modelling framework. We estimated solute transport parameters using three distinct, hypothetical spatial patterns of lateral inflow and outflow, all based on variations of the same five-parameter model structure. We compared optimized parameter values to those resulting from a distinct four-parameter model structure meant to represent the standard application of the TSM, in which only lateral inflow was implemented for net gaining reaches or only lateral outflow for net losing reaches. In the five-parameter model, solute mass was stored predominantly in the transient storage zone and slowly released back to the stream. Conversely, solute mass was predominantly removed from the stream via flow losses in the four-parameter model structure. This led to contrasting estimates of solute transport parameters and subsequent interpretation of solute transport dynamics. Differences in parameter estimates across variations of the five-parameter model structure were small yet statistically significant, except for the transient storage exchange rate coefficient , for which unique determination was problematic. We also based our analysis on , the fraction of median transport time due to transient storage. Differences across configurations in estimates were consistent but small when compared to the variability of among reaches. Optimized parameter values were influenced dominantly by the model structure (four versus five parameters) and then by the conceptualization of spatial arrangement of lateral fluxes along the reach for a set model structure. When boundary conditions are poorly defined, the information contained in the stream tracer breakthrough curve is insufficient to identify a single, unambiguous model structure representing solute transport simulations. Investigating lateral fluxes prior to conducting a study on transient storage processes is necessary, as assuming a certain spatial organization of these fluxes might set ill-defined bases for inter-reach comparisons. Given the difficulty in quantifying the spatial patterns and magnitudes of lateral inputs and outputs, we recommend small-scale laboratory tracer experiments with well-defined and variable boundary conditions as a complement to field studies to provide new insights into stream solute dynamics.
    Keywords: Transient Storage ; Flow Loss ; Flow Gain ; Otis ; Uncertainty ; Model Structure ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 3
    Language: English
    In: Journal Of Geophysical Research-Space Physics, 2011, Vol.116
    Description: The mobilization of mercury and dissolved organic carbon (DOC) during snowmelt often accounts for a major fraction of the annual loads. We studied the role of hydrological connectivity of riparian wetlands and upland/wetland transition zones to surface waters on the mobilization of Hg and DOC in Fishing...
    Keywords: Environmental Sciences Related To Agriculture And Land-Use ; Miljö- Och Naturvårdsvetenskap
    ISSN: 0148-0227
    E-ISSN: 21562202
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  • 4
    Language: English
    In: Journal of Hydrology, 2010, Vol.392(3), pp.219-233
    Description: The past century has seen significant research comparing snow accumulation and ablation in forested and open sites. In this review we compile and standardize the results of previous empirical studies to generate statistical relations between changes in forest cover and the associated changes in snow accumulation and ablation rate. The analysis drew upon 33 articles documenting these relationships at 65 individual sites in North America and Europe from the 1930s to present. Changes in forest cover explained 57% and 72% of the variance of relative changes in snow accumulation and ablation, respectively. The incorporation of geographic and average historic climatic information did not significantly improve the ability to predict changes in snow processes, mainly because most of the studies did not provide enough information on site characteristics such as slope and aspect or meteorological conditions taking place during the experiments. Two simple linear models using forest cover as the sole predictor of changes in snow accumulation and ablation are provided, as well as a review of the main sources of variation that prevent the elaboration of more accurate multiple regression models. Further studies should provide detailed information regarding the main sources of variation influencing snow processes including the effect of year-to-year changes in weather variables during the monitoring period.
    Keywords: Snow Processes ; Forest Structure ; Forest Cover ; Snow Models ; Empirical Studies ; Snow Hydrology ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 5
    In: Hydrological Processes, 15 August 2015, Vol.29(17), pp.3649-3664
    Description: A network of 30 standalone snow monitoring stations was used to investigate the snow cover distribution, snowmelt dynamics, and runoff generation during two rain‐on‐snow (ROS) events in a 40 km montane catchment in the Black Forest region of southwestern Germany. A multiple linear regression analysis using elevation, aspect, and land cover as predictors for the snow water equivalent (SWE) distribution within the catchment was applied on an hourly basis for two significant ROS flood events that occurred in December 2012. The available snowmelt water, liquid precipitation, as well as the total retention storage of the snow cover were considered in order to estimate the amount of water potentially available for the runoff generation. The study provides a spatially and temporally distributed picture of how the two observed ROS floods developed in the catchment. It became evident that the retention capacity of the snow cover is a crucial mechanism during ROS. It took several hours before water was released from the snowpack during the first ROS event, while retention storage was exceeded within 1 h from the start of the second event. Elevation was the most important terrain feature. South‐facing terrain contributed more water for runoff than north‐facing slopes, and only slightly more runoff was generated at open compared to forested areas. The results highlight the importance of snowmelt together with liquid precipitation for the generation of flood runoff during ROS and the large temporal and spatial variability of the relevant processes. Copyright © 2015 John Wiley & Sons, Ltd.
    Keywords: Rain‐On‐Snow ; Runoff Generation ; Spatio‐Temporal Variability ; Snowmelt ; Catchment Hydrology ; Flood
    ISSN: 0885-6087
    E-ISSN: 1099-1085
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  • 6
    In: Water Resources Research, March 2014, Vol.50(3), pp.2533-2550
    Description: The spatial and temporal dynamics of seasonal snow covers play a critical role for many hydrological, ecological, and climatic processes. This paper presents a new, innovative approach to continuously monitor these dynamics using numerous low‐cost, standalone snow monitoring stations (SnoMoS). These stations provide snow and related meteorological data with a high temporal and spatial resolution. Data collected by SnoMoS include: snow depth, surface temperature, air temperature and humidity, total precipitation, global radiation, wind speed, and barometric pressure. A total of 99 sensors were placed over the winters 2010/2011 and 2011/2012 at multiple locations within three 40–180 km basins in the Black Forest region of Southern Germany. The locations were chosen to cover a wide range of slopes, elevations, and expositions in a stratified sampling design. Furthermore, “paired stations” located in close proximity to each other, one in the open and one underneath various forest canopies, were set up to investigate the influence of vegetation on snow dynamics. The results showed that considerable differences in snow depth and, therefore, snow water equivalent (SWE) are present within the study area despite its moderate temperatures and medium elevation range (400–1500 m). The relative impact of topographical factors like elevation, aspect, and of different types of forest vegetation were quantified continuously and were found to change considerably over the winter period. The recorded differences in SWE and snow cover duration were large enough that they should be considered in hydrologic and climate models. A network of low‐cost stations can effectively monitor the snow cover evolution Knowledge of temporal and spatial distribution of snow cover is crucial Impact of topography and vegetation on snow cover changes over winter
    Keywords: Snow Cover ; Distribution ; Monitoring
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 7
    In: Water Resources Research, January 2012, Vol.48(1), pp.n/a-n/a
    Description: Paired watershed studies have limited researchers wishing to disentangle road and harvesting effects on peak flows or to study management schemes other than the existing scenario. The outcomes of many paired watershed studies examining peak flows have also recently been challenged since only an approach that pairs peak flows by frequency can adequately evaluate the effects of harvesting on peak flows. This study takes advantage of a model that has been developed and extensively tested at a site containing a rich set of internal catchment process observations to examine the isolated and combined effects of roads and harvesting on the peak flow regime of a snow‐dominated catchment for return periods of up to 100 years. Contrary to the prevailing perception in forest hydrology, the effects of harvesting are found to increase with return period, which is attributable to the uniqueness of peak flow runoff generation processes in snow‐dominated catchments. Planned harvesting (50% harvest area) is found to have a significant effect (9%–25% over control) on peak flows with recurrence intervals ranging 10–100 years. Peak flow frequency increases after harvesting increase with return period, with the largest events (100 year) becoming 5–6.7 times more frequent, and medium‐sized events (10 year) becoming 1.7–2 times more frequent. Such changes may have substantial ecological, hydrological, and geomorphological consequences within the watershed and farther downstream. Study findings suggest that peak flow regimes are fairly tolerant to the current level of harvesting in this particular watershed but that further harvesting may affect this element significantly. Impacts increase with flood return period, contrary to prevailing perception Magnitude of all flood sizes increases following logging Floods become more frequent following logging, especially more extreme ones
    Keywords: Dhsvm ; Forest ; Logging ; Peak Flow ; Roads ; Snow
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 8
    In: Hydrological Processes, 15 July 2014, Vol.28(15), pp.4433-4448
    Description: Current methods to estimate snow accumulation and ablation at the plot and watershed levels can be improved as new technologies offer alternative approaches to more accurately monitor snow dynamics and their drivers. Here we conduct a meta‐analysis of snow and vegetation data collected in British Columbia to explore the relationships between a wide range of forest structure variables – obtained from Light Detection and Ranging (LiDAR), hemispherical photography (HP) and Landsat Thematic Mapper – and several indicators of snow accumulation and ablation estimated from manual snow surveys and ultrasonic range sensors. By merging and standardizing all the ground plot information available in the study area, we demonstrate how LiDAR‐derived forest cover above 0.5 m was the variable explaining the highest percentage of absolute peak snow water equivalent () (33%), while HP‐derived leaf area index and gap fraction (45° angle of view) were the best potential predictors of snow ablation rate (explaining 57% of variance). This study reveals how continuous data from ultrasonic sensors are fundamental to obtain statistically significant relationships between snow indicators and structural metrics by increasing mean by 20% when compared to manual surveys. The relationships between vegetation and spectral indices from Landsat and snow indicators, not explored before, were almost as high as those shown by LiDAR or HP and thus point towards a new line of research with important practical implications. While the use of different data sources from two snow seasons prevented us from developing models with predictive capacity, a large sample size helped to identify outliers that weakened the relationships and suggest improvements for future research. A concise overview of the limitations of this and previous studies is provided along with propositions to consistently improve experimental designs to take advantage of remote sensing technologies, and better represent spatial and temporal variations of snow. Copyright © 2013 John Wiley & Sons, Ltd.
    Keywords: Hydrologic Models ; Snow Water Equivalent ; Snow Ablation Rate ; Lidar ; Hemispherical Photography ; Landsat
    ISSN: 0885-6087
    E-ISSN: 1099-1085
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  • 9
    In: Hydrological Processes, 30 May 2017, Vol.31(11), pp.2000-2015
    Description: One of the most important functions of catchments is the storage of water. Catchment storage buffers meteorological extremes and interannual streamflow variability, controls the partitioning between evaporation and runoff, and influences transit times of water. Hydrogeological data to estimate storage are usually scarce and seldom available for a larger set of catchments. This study focused on storage in prealpine and alpine catchments, using a set of 21 Swiss catchments comprising different elevation ranges. Catchment storage comparisons depend on storage definitions. This study defines different types of storage including definitions of dynamic and mobile catchment storage. We then estimated dynamic storage using four methods, water balance analysis, streamflow recession analysis, calibration of a bucket‐type hydrological model Hydrologiska Byråns Vattenbalansavdelning model (HBV), and calibration of a transfer function hydrograph separation model using stable isotope observations. The HBV model allowed quantifying the contributions of snow, soil and groundwater storages compared to the dynamic catchment storage. With the transfer function hydrograph separation model both dynamic and mobile storage was estimated. Dynamic storage of one catchment estimated by the four methods differed up to one order of magnitude. Nevertheless, the storage estimates ranked similarly among the 21 catchments. The largest dynamic and mobile storage estimates were found in high‐elevation catchments. Besides snow, groundwater contributed considerably to this larger storage. Generally, we found that with increasing elevation the relative contribution to the dynamic catchment storage increased for snow, decreased for soil, but remained similar for groundwater storage.
    Keywords: Elevation Gradient ; Hbv ; Storage Estimation ; Swiss Alps ; Tracer Hydrology ; Transep ; Water Availability
    ISSN: 0885-6087
    E-ISSN: 1099-1085
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  • 10
    Language: English
    In: Hydrological Processes, 30 September 2011, Vol.25(20), pp.3187-3203
    Description: Hydrologic models have increasingly been used in forest hydrology to overcome the limitations of paired watershed experiments, where vegetative recovery and natural variability obscure the inferences and conclusions that can be drawn from such studies. Models are also plagued by uncertainty, however, and parameter equifinality is a common concern. Physically‐based, spatially‐distributed hydrologic models must therefore be tested with high‐quality experimental data describing a multitude of concurrent internal catchment processes under a range of hydrologic regimes. This study takes a novel approach by not only examining the ability of a pre‐calibrated model to realistically simulate watershed outlet flows over a four year period, but a multitude of spatially‐extensive, internal catchment process observations not previously evaluated, including: continuous groundwater dynamics, instantaneous stream and road network flows, and accumulation and melt period spatial snow distributions. Many hydrologic model evaluations are only on the comparison of predicted and observed discharge at a catchment outlet and remain in the ‘infant stage’ in terms of model testing. This study, on the other hand, tests the internal spatial predictions of a distributed model with a range of field observations over a wide range of hydroclimatic conditions. Nash‐Sutcliffe model efficiency was improved over prior evaluations due to continuing efforts in improving the quality of meteorological data collection. Road and stream network flows were generally well simulated for a range of hydrologic conditions, and snowpack spatial distributions were well simulated for one of two years examined. The spatial variability of groundwater dynamics was effectively simulated, except at locations where strong stream–groundwater interactions exist. Model simulations overall were quite successful in realistically simulating the spatiotemporal variability of internal catchment processes in the watershed, but the premature onset of simulated snowmelt for one of the simulation years has prompted further work in model development. Copyright © 2011 John Wiley & Sons, Ltd.
    Keywords: Dhsvm ; Snow ; Road ; Logging ; Groundwater ; Stream
    ISSN: 0885-6087
    E-ISSN: 1099-1085
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