No description available.

A large portion of the freshwater in western Canada originates as snowpack from the northern Rocky Mountains. The temperature and precipitation in these areas controls the amount of snow accumulated and stored throughout the winter, and the amount and timing of melt that occurs during the spring freshet. Therefore, a better understanding of past and future changes to the extent of snowpack and timing of melt can modify the timing of peak river flow on a continental scale. Trends in temperature, precipitation, snow accumulation, and snowmelt are examined using the Mann-Kendall non-parametric test on a high resolution gridded climate dataset over western Canada for the period 1950-2010. In addition, projected changes in temperature, precipitation, snow water equivalent, and snowmelt are examined through comparison of the current (1971-2000) and future (2041-2070) time periods incorporating several regional climate models. The temporal and spatial analyses of these key hydroclimatic variables indicate that changes vary greatly over space and time. Results reveal that while both maximum and minimum temperature have increased in the past 60 years, minimum temperature has increased more than maximum temperature and is likely to continue doing so in the future. This trend is particularly evident during the colder months of the year, and at higher elevations, contributing to earlier spring melt. Between 1950 and 2010, precipitation has decreased throughout the colder months of the year and increased in the warmer months, particularly in the northern half of the study area. Future projections show increased precipitation, specifically in the north. Throughout the historical period snow accumulation has experienced decreases across the study area and through all months of the year, except for increases at high elevations. In the coldest months of the year snow accumulation is projected to increase in high elevation and northern areas while decreasing across the rest of study area in the future. Snowmelt results indicate slight increases in mid-winter melt events and an earlier onset of the spring freshet; this change is expected to continue into the future period. This study provides a summary of detected trends and potential future changes in key hydroclimatic variables across western Canada with regard to the effects these changes can have on the spring freshet and streamflow, and thus water resources, throughout the study area. / Graduate / 0368

A large portion of the freshwater in western Canada originates as snowpack from the northern Rocky Mountains. The temperature and precipitation in these areas controls the amount of snow accumulated and stored throughout the winter, and the amount and timing of melt that occurs during the spring freshet. Therefore, a better understanding of past and future changes to the extent of snowpack and timing of melt can modify the timing of peak river flow on a continental scale. Trends in temperature, precipitation, snow accumulation, and snowmelt are examined using the Mann-Kendall non-parametric test on a high resolution gridded climate dataset over western Canada for the period 1950-2010. In addition, projected changes in temperature, precipitation, snow water equivalent, and snowmelt are examined through comparison of the current (1971-2000) and future (2041-2070) time periods incorporating several regional climate models. The temporal and spatial analyses of these key hydroclimatic variables indicate that changes vary greatly over space and time. Results reveal that while both maximum and minimum temperature have increased in the past 60 years, minimum temperature has increased more than maximum temperature and is likely to continue doing so in the future. This trend is particularly evident during the colder months of the year, and at higher elevations, contributing to earlier spring melt. Between 1950 and 2010, precipitation has decreased throughout the colder months of the year and increased in the warmer months, particularly in the northern half of the study area. Future projections show increased precipitation, specifically in the north. Throughout the historical period snow accumulation has experienced decreases across the study area and through all months of the year, except for increases at high elevations. In the coldest months of the year snow accumulation is projected to increase in high elevation and northern areas while decreasing across the rest of study area in the future. Snowmelt results indicate slight increases in mid-winter melt events and an earlier onset of the spring freshet; this change is expected to continue into the future period. This study provides a summary of detected trends and potential future changes in key hydroclimatic variables across western Canada with regard to the effects these changes can have on the spring freshet and streamflow, and thus water resources, throughout the study area. / Graduate / 0368

Upland environments are important sources of mercury (Hg) to downstream wetlands and water bodies. Hydrology is instrumental in facilitating Hg transport within, and export from watersheds. Two complementary studies were conducted to assess the role hydrological processes play in controlling Hg mobility and transport in forested uplands. A field study compared runoff and Hg fluxes from three, replicate hillslope plots during two contrasting spring snowmelt periods, in terms of snowpack depth and timing. Hillslope Hg fluxes were predominately flow-driven. The melting of soil frost significantly delayed a large portion of the Hg flux later into the spring following a winter with minimal snow accumulation. A microcosm laboratory study using a stable Hg isotope tracer applied to intact soil cores investigated the relative controls of soil moisture and precipitation on Hg mobility. Both hydrologic factors control the mobility of contemporary Hg; with greatest Hg flushing from dry soils under high-flow conditions.

The frequency, magnitude, and atmospheric drivers of winter hydroclimatic conditions conducive to snowmelt in western Canada were evaluated. These hydroclimatic variables were linked to the mid-winter break-up of river ice that included the creation of a comprehensive database including 46 mid-winter river ice break-up events in western Canada (1950-2008) and six events in Alaska (1950-2014). Widespread increases in above-freezing temperatures and spatially diverse increases in rainfall were detected over the study period (1946-2012), particularly during January and March. Critical elevation zones representing the greatest rate of change were identified for major river basins. Specifically, low-elevation (500-1000 m) temperature changes dominated the Stikine, Nass, Skeena, and Fraser river basins and low to mid-elevation changes (700-1500 m) dominated the Peace, Athabasca, Saskatchewan, and Columbia river basins. The greatest increases in rainfall were seen below 700 m and between 1200-1900 m in the Fraser and at mid- to high-elevations (1500-2200 m) in the Peace, Athabasca, and Saskatchewan river basins. Daily synoptic-scale atmospheric circulation patterns were classified using Self-Organizing Maps (SOM) and corresponding hydroclimatic variables were evaluated. Frequency, persistence, and preferred shifts of identified synoptic types provided additional insight into characteristics of dominant atmospheric circulation patterns. Trend analyses revealed significant (p < 0.05) decreases in two dominant synoptic types: a ridge of high pressure over the Pacific Ocean and adjacent trough of low pressure over western Canada, which directs the movement of cold, dry air over the study region, and zonal flow with westerly flow from the Pacific Ocean over the study region. Conversely, trend analyses revealed an increase in the frequency and persistence of a ridge of high pressure over western Canada over the study period. However, step-change analysis revealed a decrease in zonal flows and an increase in the occurrence of high-pressure ridges over western Canada in 1977, coinciding with a shift to a positive Pacific Decadal Oscillation regime. A ridge of high pressure over western Canada was associated with a high frequency and magnitude of above-freezing temperatures and rainfall in the study region. This pattern is highly persistent and elicits a strong surface climate response. A ridge of high pressure and associated above-freezing temperatures and rainfall was also found to be the primary driver of mid-winter river ice break-up with rainfall being a stronger driver west of the Rocky Mountains and temperature to the east. These results improve our understanding of the drivers of threats to snowpack integrity and the generation of extreme hydrologic events. / Graduate

La prévision des crues de l'Isère en amont de Grenoble est une préoccupation majeure du SPC AN qui souhaite faire évoluer son système en intégrant une prévision hydrométéorologique, afin de pouvoir étendre les délais d'anticipation. Ce bassin, de régime à dominante nivale intégre un important dispositif hydroélectrique modifiant le régime naturel des écoulements. Le sous-bassin de l'Isère à Moûtiers, d'une surface proche du millier de km2, comportant les caractéristiques typiques de l'ensemble du bassin, constitue une zone test idéale qui permettra d'appréhender judicieusement la modélisation hydrologique complète à terme du bassin de l'Isère à Grenoble. Dans le cadre du projet ALCOTRA - RiskNat, le modèle RS2 (Dubois et al.,2000) développé au LCH-EPFL et adapté au contexte Alpin constitue un bon compromis entre une approche qui permet d'intégrer les spécificités de la zone d'étude et une souplesse de mise en oeuvre, qui sur le plan opérationnel, est un atout capital. La complexité du réseau hydraulique en présence a impliquée une modélisation en deux étapes : calibration du modèle en conditions naturelles puis intégration des ouvrages. A partir de la représentation des aménagements dans le modèle, plusieurs discrétisations spatiales du bassin plus ou moins détaillées ont été imaginées et testées dans un premier temps. Cela a permis d'analyser l'impact de ces différentes représentations des forçages météorologiques sur les termes du bilan hydrologique simulé. Ce contexte de montagne rend particulièrement délicat l'estimation du forçage des précipitations. L'impact de 3 champs de précipitation testés en entrée du modèle sur les simulations de débit a été analysé et s'est révélé bien plus important que celui lié à la discrétisation des forçages météorologiques. Le modèle capable de représenter le mieux possible la météorologie du bassin a été conservé afin d'y représenter les aménagements dans un second temps. Une méthode simple pour les considérer peut s'avérer suffisante, et une relation d'équivalence pour la représentation des prises d'eau permet de favoriser la souplesse du modèle. Néanmoins, à terme, cet outil doit permettre au SPC de se baser sur une estimation plus juste et plus précise du débit de crue, ce qui exige d'intégrer un pas de temps plus fin, i.e. l'horaire, adapté au temps de réponse du bassin. La mise en œuvre de cette prévision horaire est alors plus complexe et requiert une représentation plus détaillée des processus hydrométéorologiques et hydrauliques. Une méthode de désagrégation temporelle pour estimer le forçage des précipitations a été employée. Des premiers résultats encourageants de modélisation horaire sont présentés. / The flood forecasting of the Isere River upstream Grenoble is a major concern of the SPC NA wanting to change its system to an integrated hydrometeorological forecasting to extend the time of anticipation. This basin whose surface is about several thousand kilometers square and with a snowmelt dominated regime, integrate an important hydro-electric device modifying the flows natural regime. The Moûtiers Isere River subbasin, with a surface close thousands of square kilometers and the typic characteristics of the entire basin, is a ideal test zone that will appropriately apprehend the hydrological modeling of Grenoble Isere River basin. In the framework of ALCOTRA -RiskNat project RS2 Model developed at the LCH-EPFL (Dubois et al., 2000) and adapted to the Alpine context is a good compromise between an approach that integrates the large specificity of the study area and flexibility of implementation, which operationally is a considerable asset. The complexity of this hydraulic network implied a two steps modeling : model calibration in natural conditions then integration of the hydro-electric device. From the representation of hydropower plants in the model, four spatial discretizations of the basin more or less detailed, have been devised and tested in the first place. This was used to analyze the impact of four different representations of meteorological forcing on the simulated water balance terms. This mountain context makes it particularly difficult estimating the precipitation forcing. The impact of three precipitation fields tested as input to the model on simulations of flow has proved far greater than that associated with the discretization of the meteorological forcing. The model that best represent the meteorology of the basin has been preserved in order to represent the hydropower plant for a second time. A simple method to consider may be sufficient, and an equivalence relation for the representation of water intake helps to promote flexibility of the model. However, over time, this tool must allow the SPC forecasting to be based on an estimate fairer and more accurate flood flow, which requires integrating a finer time step, the hourly time step, suitable basin response time. The implementation of this hourly forecasting is more complex and requires a more detailed process of hydro-meteorological and hydraulics. For estimating the new precipitation forcing, a method of temporal disaggregation was used. Encouraging initial results of hourly modeling are presented.

Abstract This thesis examined hydrological processes such as snowmelt and groundwater discharge in drained peatland areas in the boreal zone. The studied processes were measured in situ using environmental tracers. Further, performance of a treatment wetland was studied during snowmelt and high flow. A GIS model was developed to estimate groundwater seepage areas in peatland systems surrounding eskers. It was found that soil frost had a clear impact on water quality during snowmelt. This was evident as lower suspended sediments, water colour and dissolved organic carbon concentrations, among other changes. The treatment wetland was found to reduce the suspended solids load during the snowmelt period and late autumn, while reductions in phosphorus and nitrogen loads occurred during summer. A sampling algorithm was built to test how different sampling frequencies affected the estimation of suspended solid loads from the constructed wetland. The results showed increasing uncertainty for sparser sampling (from weekly to monthly sampling), but the uncertainty remained high even at weekly sampling. The GIS model was tested on two eskers and shown to give a fair estimate of groundwater discharge locations. It can thus be used for improving aquifer protection in boreal eskers related to the drainage networks surrounding them. However, to be applied more widely, further efforts are required. The findings in this thesis could be used to develop better water management policies for peat extraction areas, or other industries operating in similar soils and climate. For example, meltwater could be allowed to temporarily bypass treatment facilities in areas with deep soil frost penetration. The wetland study showed that peatland-based wetlands are a suitable approach for improving water treatment performance even under variable hydraulic loads. The uncertainty in the estimated load from a small peat extraction catchment was high, which might limit the use of such data for some purposes. Load estimation methods using the concentration data collected during previous years might be able to reduce the uncertainty, but if the uncertainty needs to be lowered substantially use of sensor technology might be the only viable approach. / Tiivistelmä Tämä väitöskirja käsittelee lumensulannasta syntyvää valuntaa erilaisilla turvemailla ja pintavalutuskentän puhdistustehoa lumensulannan aikaan turvetuontantoalueella. Lisäksi työssä pohditaan miten erilainen näytteenottoohjelma vaikuttaa turvetuotantoalueilta arvioituun kiintoaine kuormitukseen ja kehitetään yleiseen paikkatietoaineistoon perustuva malli jolla on mahdollista ennustaa pohjaveden purkatumispaikkoja harjualueilla. Routaisella turvetuotantoalueelta kiintoaineen, värin ja liuenneen orgaanisen hiilen pitoisuudet olivat pieniä lumensulannan aikaan. Työssä seurattu pintavalutuskenttä vähensi kiintoainekuormitusta alapuoliseen vesistöön myös lumensulannan ja syksyn aikana. Ravinteiden osalta pintavalutuskentän toiminta oli parasta kesäaikaan, lumensulannan ja syksyn aikana havaittiin typen ja fosforin huuhtoutumista. Eri näytteenotto-ohjelmilla havaittiin olevan suuri vaikutus arvioituun kuormitukseen. Yleisesti voidaan sanoa epävarmuuden kasvavan kohti harvempaa näytteenotto väliä (viikoittainen-kuukausittainen), mutta, myös viikoittaisella näytteenotolla epävarmuus on huomattava. Kehitettyä paikka- tietomallia kokeiltiin kahdella harjulla jossa se pystyi antamaan suuntaa antavaa arvioita pohjaveden purkautumispaikoista. Työn tuloksia voidaan hyödyntää turvetuotannon tai muiden turvemailla tai niiden lähellä sijaitsevien teollisuuden vesistövaikutuksia arvioitaessa. Esimerkiksi routaisella turvemaalla voitaisiin harkita lumensulannasta aiheituvan valunnan ohijuoksutusta vesiensuojelurakenteista. Työssä todettiin myös pintavalutuskenttien toimivan vaihtelevan kuormituksen alaisena, sekä lumensulannan että syksyn aikaan. Arvioiduissa kuormituksissa erinäytteenottoväleillä havaitut suuret epävarmuudet saattavat rajoittaa laskelmien käyttöä joissakin tarkoituksissa. Epävarmuutta voidaan vähentää käyttämällä hyväksi edellisinä vuosina tehtyjä vedenlaatumittauksia. Luotettavin tapa epävarmuuden vähentämiseksi on jatkuvatoimisten vedenlaatumittareiden käyttäminen.

Mercury (Hg) transport in streams is typically facilitated by dissolved organic matter (DOM), however, the dynamics of Hg and DOM during snowmelt in montane watersheds are poorly understood. Hg transport during snowmelt is widely recognized as a significant source of Hg to downstream lakes and reservoirs, such as Jordanelle Reservoir where fish consumption advisories are in effect due to elevated Hg concentrations in certain species of fish. For this study, total mercury (THg), methylmercury (MeHg), and DOM samples were collected at three sites in the upper Provo River, northern Utah, during the 2016 and 2017 water years. To evaluate Hg and DOM sources, samples were collected from snowpack and ephemeral streams in the watershed. In-situ fluorescent DOM (fDOM) data and other parameters were measured in the river to characterize high-frequency variation in water chemistry. Excitation-emissions matrices (EEMs) were used to determine changes in DOM characteristics during snowmelt. Hg concentrations increased in the upper Provo River from /L during baseflow to >;7 ng/L during the snowmelt period (~April-July), with filtered THg concentrations approximately ~75% of the unfiltered concentrations. In the watershed, filtered THg concentrations ranged from ~0.4 ng/L in snowpack to ~8 ng/L in ephemeral streams. Annual THg loading from the Provo River to Jordanelle Reservoir was approximately 1 kg/yr with ~90% of the flux occurring during the snowmelt period. High correlations between filtered THg and fDOM allowed for the development of a high frequency filtered THg proxy using in-situ fDOM sensors. DOM characteristic during the snowmelt period showed that Hg transport was facilitated by humic substances which was sourced from upland soils. Fractions of filtered methylmercury (MeHg) and filtered THg (filtered MeHG:filtered THg) were ~0.1 during baseflow and reduced to ~0.01 during snowmelt, implying that snowmelt runoff has little impact on the MeHg flux to Jordanelle Reservoir. The results suggest that Hg and DOM are flushed from soils during snowmelt, and that a significant majority of the Hg flux occurs the snowmelt period. Our study has implications for understanding Hg sources and transport mechanisms in other snowmelt dominated watersheds.

No description available.

Snow represents an important resource in mountainous regions. Monitoring its extent and amount is relevant for several applications, such as hydrology, ecology, avalanche monitoring, or hydropower production. However, a correct understanding of the high spatial and temporal variability of snow accumulation, redistribution and ablation processes requires its monitoring in a spatialized and detailed way. Recently, the launch of the Sentinel missions has opened the doors to new approaches that mainly exploit high resolution (HR) data having a spatial detail of few dozens of m. In this thesis, we aimed at exploiting these new sources of information to retrieve important parameters related to the snowmelt processes. In detail, we i) investigated the use of Sentinel-1 Synthetic Aperture Radar (SAR) observations to evaluate snowmelt dynamics in alpine regions, ii) developed a novel approach based on a hierarchical multi-resolution analysis of optical time-series to reconstruct the daily HR snow cover area (SCA), and iii) explored the combination of HR SCA time-series, SAR snowmelt information and other multi-source data to reconstruct a daily HR snow water equivalent (SWE) time-series. In detail, in the first work we analyzed the relationship between the snowmelt phases of a snowpack and the multi-temporal SAR backscattering. We found that the SAR is able to provide useful information about the moistening, ripening and runoff phases. In the second work, we exploited the snow pattern repetition on an inter-annual basis driven by the geomorphological features of a study area to carry out historical analyses. Thus, we took advantage of these repeated patterns to fuse low resolution and HR satellite optical data and set up a gap filling to derive daily HR snow cover area (SCA) time-series. These two research works are the pillars for the last contribution, which aims at combining all these information sources together with both in-situ data and a simple yet robust degree day model that provides an estimate of the potential melting to derive daily HR SWE time-series. These final results have an unprecedented spatial detail, that allows to sample the phenomena linked to the complex snow accumulation, redistribution and ablation processes with the required spatial and temporal resolution. The methodology and the results of each experimental work are illustrated and discussed in detail in the chapters of this thesis, with a look on further research and potential applications.