Modelling snow and runoff patterns in Swiss mountain environments under conditions of climate change

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Thesis

Reference

Modelling snow and runoff patterns in Swiss mountain environments under conditions of climate change

UHLMANN-SCHNEITER, Bastienne

Abstract

Les montagnes sont particulièrement exposées aux changements climatiques. Il a en effet été observé que la moindre modification atmosphérique est accentuée dans un tel environnement en raison de la topographie complexe et du fort gradient altitudinal du terrain. Or, les Alpes en général et plus particulièrement en Suisse sont considérées comme le « château d'eau » de l'Europe puisqu'elles constituent la source de nombreux fleuves du continent. A cela s'ajoute leur rôle essentiel dans l'écosystème et leur fonction socio-économique conséquente (notamment dans le tourisme ou la production hydroélectrique) qui leur confèrent une importance capitale. Leur influence s'étend en outre bien au-delà de leurs limites territoriales.

Par conséquent, le réchauffement climatique, mesuré depuis l'ère post-industrielle et dont la tendance simulée ne montre aucun signe de fléchissement pour la fin du siècle, pourrait avoir de sérieuses répercussions dans cet environnement. Ce travail se propose donc d'investiguer les impacts physiques d'un réchauffement climatique dans les montagnes helvétiques, plus [...]

UHLMANN-SCHNEITER, Bastienne. Modelling snow and runoff patterns in Swiss

mountain environments under conditions of climate change . Thèse de doctorat : Univ.

Genève, 2011, no. Sc. 4388

URN : urn:nbn:ch:unige-184870

DOI : 10.13097/archive-ouverte/unige:18487

Available at:

http://archive-ouverte.unige.ch/unige:18487

Disclaimer: layout of this document may differ from the published version.

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UNIVERSITÉ DE GENÈVE FACULTÉ DES SCIENCES Institut des Sciences de l’Environnement Professeur Martin Beniston

Modelling Snow and Runoff Patterns in Swiss Mountain Environments Under Conditions

of Climate Change

THÈSE

présentée à la Faculté des Sciences de l’Université de Genève pour obtenir le grade de Docteur ès Sciences, mention environnement

par

Bastienne UHLMANN-SCHNEITER de

Amsoldingen (BE)

Thèse N° 4388

GENÈVE

Atelier d’impression ReproMail 2011

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Remerciements

La première personne que je tiens à remercier du fond du cœur est Martin Beniston, qui a cru en moi, parfois plus que moi-même, dès notre première rencontre. Il a toujours pris la peine de répondre à mes questions, de m’aiguiller dans la direction la plus appropriée et a de cette manière contribué à faciliter mon passage du monde météorologique au monde climatique. Il m’a également donné l’opportunité d’aller à la rencontre d’autres chercheurs par le biais de conférences nationales et internationales, ce qui n’a pas manqué d’enrichir le fruit de mes recherches. J’aimerais aussi le remercier pour les corrections scientifiques et linguistiques de mon manuscrit.

Stéphane Goyette a également favorisé l’élaboration et l’aboutissement de ce travail. Il m’a non seulement appris toute la base de la modélisation numérique – et certainement bien davantage – mais aussi transmis les fondements nécessaires à la rédaction d’articles scientifiques. Sa relecture attentive de mon manuscrit a sans aucun doute concouru à améliorer la qualité de cette recherche et je lui en suis très reconnaissante.

Je souhaite également remercier Frédéric Jordan qui m’a guidée dans l’univers de l’eau.

L’enthousiasme qui l’habite lorsqu’il s’agit de mettre en avant le modèle hydrologique qu’il m’a mis à disposition est tout à fait contagieux et ses patientes explications ont fini de me convaincre quant à l’efficacité de cet outil.

J’adresse aussi mes remerciements à Ignacio López-Moreno et Vera Slaveykova qui ont accepté de faire partie de mon jury de thèse.

Il m’a été donné de partager ces quelques années avec d’autres personnes qui ont toutes, à leur manière, laissé une trace dans ce travail. Merci donc à Camille Gonseth et Javier García-Hernández pour leurs conseils économiques et hydrologiques respectivement et aux membres de l’Institut des Sciences de l’Environnement Anthony Lehmann, Marjorie Perroud, Christophe Etienne, Nicole Gallina, Ramona Maggini, Margot Hill, Maura Brunetti et Charles-Antoine Kuszli

Je voudrais pour finir remercier infiniment mes proches qui m’ont soutenue sans faille tout au long de ce parcours. Je pense tout particulièrement à mon mari David, sans qui cette thèse n’existerait pas : il fut d’un soutien inconditionnel, tant du point de vue psychologique que logistique. Je pense à mes enfants Eloïse et Félicien qui sont venus au monde durant ce doctorat et qui, s’ils ont reporté le point final de ce travail, m’ont insufflé beaucoup d’énergie. Je pense à mes parents Anne-Marie et Louis et à ma sœur Pauline qui ont su me faire avancer notamment dans les moments plus difficiles. Je pense enfin au reste de ma famille et à mes amis qui sont restés à mes côtés et qui m’ont toujours encouragée.

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Résumé

Les montagnes sont particulièrement exposées aux changements climatiques. Il a en effet été observé que la moindre modification atmosphérique est accentuée dans un tel environnement en raison de la topographie complexe et du fort gradient altitudinal du terrain. Or, les Alpes en général et plus particulièrement en Suisse sont considérées comme le « château d’eau » de l’Europe puisqu’elles constituent la source de nombreux fleuves du continent. A cela s’ajoute leur rôle essentiel dans l’écosystème et leur fonction socio-économique conséquente (notamment dans le tourisme ou la production hydro- électrique) qui leur confèrent une importance capitale. Leur influence s’étend en outre bien au-delà de leurs limites territoriales. Par conséquent, le réchauffement climatique, mesuré depuis l’ère post-industrielle et dont la tendance simulée ne montre aucun signe de fléchissement pour la fin du siècle, pourrait avoir de sérieuses répercussions dans cet environnement. Ce travail se propose donc d’investiguer les impacts physiques d’un réchauffement climatique dans les montagnes helvétiques, plus précisément dans le domaine de la neige et de l’eau durant ces prochaines décennies.

Dans la première partie de ce travail, une analyse des conditions d’enneigement dans les milieux montagneux suisses a été menée. Tout d’abord, l’évolution du manteau neigeux a pu être évaluée dans différentes régions pour la fin du siècle à l’aide d’un modèle numérique de bilan énergétique de surface, appelé GRENBLS. Les intrants horaires (températures, précipitations et points de rosée) nécessaires au fonctionnement du modèle ont été perturbés afin de reproduire un réchauffement climatique à la fin du siècle (pour la période 2071-2100). Afin de ne pas modifier les intrants de manière uniforme et conserver les variations naturelles des séries de variables, l’amplitude saisonnière de ces changements atmosphériques a été dictée par les résultats du modèle régional de climat HIRHAM, basé sur le scenario climatique A2 du Groupe d’experts Intergouvernemental sur l’Evolution du Climat (GIEC). Les simulations de GRENBLS montrent que les régions qui connaissent actuellement des hivers en moyenne peu enneigés (ouest de la Suisse, Préalpes et Alpes bernoises) seraient aussi les régions les plus vulnérables face à un réchauffement climatique.

En raison de l’augmentation récente de la valeur économique de la neige, notamment dans le domaine du tourisme hivernal, l’étude a été ensuite approfondie en analysant l’évolution de l’enneigement dans 20 domaines skiables répartis sur l’ensemble du territoire au nord des Alpes. Le modèle projette une diminution de la couverture neigeuse, ainsi qu’un raccourcissement de la saison hivernale dans toutes les stations de ski étudiées. Dans six d’entre elles, il n’y aurait même aucun jour skiable à la fin du siècle. L’utilisation de

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GRENBLS a en outre permis d’aller au-delà de la simple relation entre l’altitude d’une station et son enneigement : les caractéristiques régionales générées par les différentes expositions, inclinaisons des pentes et localisations des stations dans le pays doivent également être prises en compte pour une évaluation complète de la couverture neigeuse future.

La question de savoir si des hivers fortement enneigés seraient encore possibles dans un climat plus chaud peut également être posée. Afin d’y répondre, une analyse des distributions conjointes des variables de températures et précipitations a été menée. Cette méthode a permis de classer les hivers en quatre catégories liées à des situations synoptiques dominantes: froid/humide, froid/sec, chaud/humide et chaud/sec (CS). Il a donc pu être établi que le nombre d’hivers fortement enneigés était inversement proportionnel au nombre d’occurrences des situations CS. De plus, malgré une augmentation observée de la température hivernale dans les Alpes par rapport aux décennies précédentes, un enneigement abondant a été enregistré durant quelques hivers récents. En utilisant à nouveau les résultats du modèle régional HIRHAM, il a pu être montré que même si les hivers fortement enneigés tels que nous les avons parfois vécus ces dernières années ne se produiraient que 5% du temps durant la période 2071-2100, ils ne devraient pas pour autant totalement disparaître dans un climat plus chaud.

La seconde partie de cette étude traite du régime hydrologique actuel et futur du bassin versant fortement englacé de Findelen, situé dans le complexe hydro-électrique de la Grande Dixence en Valais. Le débit à l’exutoire du bassin de Findelen a été simulé à l’aide du modèle hydrologique Routing System 3 (RS3.0). Ce modèle numérique conceptuel convient particulièrement bien à la représentation de processus en milieux alpins puisqu’il est notamment composé de sous-modèles de neige et de glace. Après avoir démontré ses capacités à reproduire les valeurs observées d’écoulement et de surface glaciaire, RS3.0 a permis d’évaluer les capacités d’adaptation du débit d’eau et du glacier de ce bassin versant à un climat artificiellement maintenu dans des conditions atmosphériques de la période de référence (1961-1990) durant plus de 100 ans. Cette expérience a été élaborée dans le but de déterminer le comportement du système dans le cas théorique où la tendance actuelle de réchauffement climatique venait à cesser. Les résultats indiquent que les débits diminueraient de 15% puis se stabiliseraient après un peu moins de 50 ans.

D’autre part, le glacier perdrait 3.5% de sa surface durant le même laps de temps avant de trouver un équilibre avec les conditions atmosphériques locales (i.e. il ne rétrécirait ni ne s’accroîtrait).

Finalement, une perturbation progressive a été appliquée aux intrants de RS3.0 jusqu’à la fin du siècle selon les résultats du modèle HIRHAM, afin de simuler un réchauffement climatique. Ainsi, une série continue de débits journaliers, ainsi qu’un aperçu de l’évolution des surfaces et épaisseurs de glace ont été obtenus. Les résultats affichent en premier lieu une augmentation des débits (19.4% en 60 ans environ) due à la fonte rapide du glacier, suivie d’une forte diminution de l’écoulement jusqu’à la fin de la période étudiée. Sur la durée totale de la simulation, le débit à l’exutoire diminuerait de 28%, tandis que le glacier de Findelen perdrait 91% de sa surface. En ce qui concerne la saisonnalité des écoulements, RS3.0 montre dans un climat plus chaud une fonte de neige et de glace plus précoce et plus importante au printemps alors que les valeurs de débits seraient plus basses le reste de l’année en raison de l’épuisement des ressources glaciaires. Dès lors, le

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cycle annuel de l’eau dans ce bassin versant ne pourrait plus être caractérisé par un régime hydrologique de type glaciaire mais plutôt par un type nivo-pluvial.

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Abstract

Mountains are particularly exposed to climate change. It has been observed that minor atmospheric modifications are largely enhanced in such environments due to their complex topography and the significant altitudinal gradient of the terrain. The Alps, particularly in Switzerland, are considered as the “water tower” of Europe as they constitute the source of many rivers on the continent. Besides, not only do they play a major role in the global ecosystem but they also do assume an important socio-economic function (namely in tourism or hydropower). Moreover, their influence extends both to nearby areas and to far downstream regions. Hence, the atmospheric warming, measured since the post-industrial age and where simulated trends reveal no sign of relenting for the end of the century, could have serious repercussions in this environment. This study intends therefore to investigate the physical impacts of climate change on snow and water in the Swiss mountains during the next decades.

In the first part of the research, an analysis of snow patterns in Swiss mountain environments has been conducted. The evolution of snow cover in different regions has been first addressed by means of a surface energy balance model called GRENBLS. The hourly input (temperature, precipitation and dew point temperature) that drives the model has been perturbed in order to reproduce a climate warming by the end of the century (for the 2071-2100 period). To avoid a uniform forcing and to preserve the natural variations of the time series, the seasonal amplitude of these atmospheric changes is suggested by the output of the regional climate model HIRHAM, under the climate scenario A2 of the Intergovernmental Panel on Climate Change (IPCC). The simulations of GRENBLS show that the regions which already currently have little snow (Western Switzerland, Prealps and Bernese Alps) are the one that would be the most vulnerable in a warmer climate.

Due to the recent increase in the economic value of snow, in particular in the context of winter tourism, the study has next been enlarged with the analysis of snow patterns within 20 selected ski areas throughout the northern part of the Swiss Alps. The model shows a decrease of the snow depths and duration in every studied ski fields. Six of them do not even encounter a single skiable day at the end of the century. The use of GRENBLS has also enabled to go beyond the simple relation between altitude and amount of snow: the regional characteristics such as exposure, inclination of slopes and localization in the country must be taken into account for a complete evaluation of potential future snow patterns.

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It is also of interest to investigate whether snow-abundant winters could still occur in a warmer climate. In this perspective, an analysis of joint probability temperature/precipitation distributions has been carried out. This method has enabled to categorize winters into for modes linked to dominant synoptic situations: cold/moist, cold/dry, warm/moist and warm/dry (WD). It has thus been established that the number of snow-abundant winters was inversely proportional to the number of occurrences of WD situations. Besides, despite an observed increase in winter temperatures in the Alps during the last decades, snow- abundant winters have nonetheless occurred in past years. Using the projections of the HIRHAM regional model, results indicate that, although snow-abundant winters as experienced in recent years may occur less than 5% of the time during the period 2071- 2100, they would not totally disappear in a warmer climate.

The second part of this study deals with the current and potential future hydrological regime of the highly glacierized Findelen watershed, situated in the Grande Dixence hydropower complex in Valais. The discharge at the outlet of the Findelen catchment has been simulated with the hydrological model Routing System 3 (RS3.0). This conceptual model is particularly well conceived to represent the alpine hydrology as infiltration and runoff routines are supported by a snow and an ice sub-model. RS3.0 has shown to be very efficient in reproducing observed flows and glacier surfaces. It has thus enabled an assessment of the adaptation of runoff and glacier area/volume in the Findelen watershed to climate artificially maintained under the atmospheric conditions of the reference period (1961-1990) through to more than 100 years. This theoretical experiment was undertaken in order to give indications on the hydrological trends that would be expected if the current warming tendency were to cease. The findings reveal that the discharge values would decrease by 15% before stabilizing in a little less than 50 years. On the other hand, the Findelen glacier would lose 3.5% of its surface area during the same timeframe and would then achieve equilibrium with surrounding atmospheric conditions (i.e. the glacier would neither grow nor shrink).

Finally, a progressive perturbation to the end of the century has been applied to the input of RS3.0, according to the results of the HIRHAM with the aim of reproducing a climate warming. Thus, a continuous series of daily discharge amount and insights of the evolution of ice surface and thickness have been obtained. The results indicate in the first place an increase in runoff (19.4% in about 60 years) due to the rapid melt of the glacier, followed by a marked decrease in discharge through to the end of the studied period. During the entire simulation interval, the runoff values at the outlet would decrease by 28%, whereas the Findelen glacier would lose 91% of its surface area. Concerning the seasonality of flows, RS3.0 shows an earlier and more consequent snow and ice melt in spring in a warmer climate, while the discharge amount is lower the rest of the year primarily because of the depletion of the solid water reservoir. Therefore, the annual cycle of water in this catchment would not be characterized by a glacial hydrological regime anymore but by a more nivo- pluvial one.

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Chapter 1 Overall Introduction

The most commonly-perceived landscape in Switzerland is that of its mountain environment. Rock, ice and snow are generally the main elements that come to mind when visualising orographic features. Because mountains are subject to numerous natural hazards (landslides, snow avalanches, storms, debris flows etc.), they have long been regarded as predominantly hostile environments. Mountain regions have however gained recognition during the last century for their significant function in the global ecosystem as well as for their economic potential. Their resources are plural – as areas of recreation or sources of water for instance – and do not only bring benefits to the areas concerned but also to the connected lowlands.

The climate of Swiss mountains and uplands is mainly characterized by four major factors (Barry, 2001), namely continentality, latitude, altitude and topography of the landmasses.

The latter interact strongly with the general atmospheric circulation: they are influenced by a succession of oceanic, continental, polar, Mediterranean and, on occasion, Saharan air masses just as much as they themselves affect large-scale atmospheric flows simply by their sheer physical presence (Beniston, 2006). As a consequence, the spatial and temporal variability of the main climatic drivers which are temperature and precipitation is very large in such environments. Hence, this complexity makes them very vulnerable to atmospheric changes that can affect rainfall, snowfall, and snow and ice melt (Birsan et al., 2005). This can be illustrated by the disproportionate increase in observed yearly mean surface temperatures in the course of the 20^th century (Figure 1.1) compared to mean global warming. The interannual variability has been generally more pronounced than on a global scale and the warming exceeded 1.5 °C, which is more tha n twice the global warming average (Permanent Secretariat of the Alpine Convention, 2009). Concerning precipitation however, no global significant trend has been detected in the Alps, although spatial variability of precipitation has been considerable (Bogataj, 2007)

This rapid atmospheric warming is very likely due to the observed increase in anthropogenic greenhouse-gas (GHG) concentrations (IPCC, 2007). Over the course of the 21^st century, there is every reason to believe that the warming trend will not be attenuated with continued

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1 0.5 0 0.5 1 1.5

1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

Global Alps

1900

Year

Temperature Anomaly [C°]

Figure 1.1. Temperature departures from the 1961-1990 climatological mean in the Swiss Alps compared to global temperature anomalies, for the period 1901-2000. A five-year filter has been applied to remove interannual noise (modified from Beniston, 2005).

GHG emissions at or above current rates. Such warming will induce possible large changes not only in the physical but also in the biological and socio-economic systems that characterize the Alps (OECD, 2006). As a matter of fact, the simulations considered in the Intergovernmental Panel on Climate Change report (IPCC, 2007) suggest that the global mean surface temperature would increase by 1.4 °C to 5 .8 °C (the wide range of change is due to different climate modelling results and a set of climate scenarios based on different greenhouse-gas emission pathways) by the end of this century. In the Swiss Alps, model results show a temperature increase close to 4 °C in wint er and more than 6 °C in summer compared to the baseline 1961-1990 climate (Beniston, 2009). Changes in precipitation amount and seasonality are also expected, but the poorly resolved mountain topography in climate models leads to considerable uncertainties. However, while no unequivocal conclusions can be drawn, an increase in wintertime precipitation and a curtailed summertime rainfall amount is projected in the Alps over coming decades (Schmidli and al., 2007; Beniston et al., 2011).

Significant repercussions of global warming on mountain areas are consequently anticipated. The function of snow and water in environmental and economic systems in the Alps as well as in regions far downstream is considerable, particularly on the tourism, energy, agriculture, and ecosystem sectors (Barry, 2006). It therefore seems necessary to assess the potential changes that can affect the mountain cryosphere and hydrosphere. As an example, winter tourism in the Swiss Alps is often by far the most important source of income for many resorts (Koenig and Abegg, 1997), where snow-reliability is an essential requirement for a financially viable skiing industry (Elsasser and Bürki, 2002). Potential future snow depth and duration is an issue that has been addressed in several studies (e.g., Etchevers and Martin, 2002; OECD, 2006). The latter generally express projections of the

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future rise in the altitude of the snowline. The physical characteristics of Swiss ski resorts are very diverse, however, and a detailed analysis of representative ski areas could bring further valuable elements. From a broader perspective, several studies have examined the potential changes of average snow patterns in an enhanced greenhouse climate (Beniston et al., 2003; Keller and Goyette, 2005) but few have investigated the variability of winter snow conditions (López-Moreno et al., 2009). It is therefore of interest to examine whether snow-abundant winters could still be expected in a warmer climate, as it can have many environmental (e.g. vegetation or natural hazards) and socio-economic (e.g. hydropower or tourism) implications. Hydrological regimes in mountain areas will also be affected by climate change, which will have repercussions in the supply mechanisms for hydropower for instance. This topic has been previously analysed in the Alps for the Rhone and the Rhine basins namely by Etchevers et al. (2002), Middelkoop et al. (2001) or Westaway (2000). In this domain, glacier-fed water will definitely constitute a special case since it will be particularly exposed in a warmer climate (Huss et al., 2008; Kobierska et al., 2011). In order to evaluate this specific outcome over coming decades and to improve our understanding of local processes, a close investigation at a high temporal resolution is required, first in a stable climate, then in a warmer one.

The principal objectives of this thesis are hence to analyse different aspects of water (intimately linked to the behaviour of snow and ice) in a complex and sensitive environment under conditions of climate change. Modifications of snow patterns in Swiss mountain environments and the response of water discharge in an exploited catchment in the light of global warming are at the core of the study. The common methodology used to assess snow conditions and water resources available for skiing and energy production, respectively, through to the end of the century is based on numerical modelling. Modelling can enable a precise analysis at a local scale of the current and future evolution of snow and runoff.

This study therefore builds upon two distinct parts that are thematically related and that compose the following chapters of the thesis. Each chapter corresponds to manuscripts edited or submitted to scientific journals and can be considered to be stand-alone papers.

Part 1: quantification of the potential changes in snow amount and duration in various Swiss mountain areas and selected ski resorts under conditions of climate change with the help of a surface energy balance model (Chapter 2). Investigation of the potential occurrence of snow-abundant or snow-sparse winters through a joint distribution analysis of temperature and precipitation for present and future climate conditions (Chapter 3).

Part 2: modelling of the current discharge of a small but highly glacierized basin in the Swiss Alps with a hydrological model, and simulations of runoff throughout the 21^st century with climatic conditions identical to those encountered during the baseline period 1961 to 1990. Special attention is given to the effect of glacier imbalance on current discharge rates (Chapter 4). Thus is followed by an analysis of the physical impacts of atmospheric warming on runoff in this watershed through to the end of the century, according to the amplitude of change suggested by regional climate model simulations (Chapter 5).

Because of the very contrasted but data rich environment (in terms of availability and length of time series), Switzerland is an ideal territory to conduct investigations such as those presented in this work. Besides, a detailed analysis of water regimes through case studies

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can help assessing the hydrological significance of mountains (Viviroli et al., 2003).

Moreover, because the spatial resolution of climatic models still remains generally too crude to adequately represent most mountain areas for now, new case studies with proper downscaling methods are necessary to decrease the level of uncertainty (Beniston, 2006;

López-Moreno et al., 2009). Chapter 2 of the study is mainly linked to tourism whereas Chapter 5 is related to hydropower. Insights of these interactions are briefly discussed in the next sections of this chapter. However a subsequent analysis of the socio-economic impacts that climate change would have on both domains – as well as on other fields such as agriculture or vegetation – is beyond the scope of this dissertation. Nor will the evolution of extreme discharge quantities be addressed in the present research, as it would require a further extended examination.

The next paragraphs constitute the framework within which this research has been carried out. First, snow cover patterns and variability in Swiss mountain environments are presented, as well as the winter tourism associated to it. The hydrology of the Swiss Alpine region is described in the second place. Runoff of one of the largest exploited watershed in Canton of Valais is then more particularly examined, as it will serve as a case study in chapters 4 and 5. Further, the methodology for assessing climate, snow, and runoff changes is developed, as well as the criteria of choice for a particular model or climate scenario. The last section will give some insights of the mitigation and adaptation strategies that can be applied in the Swiss mountain environment.

1.1. Snow cover in Swiss mountains and tourism

Snow amount and duration in the Swiss mountains is highly dependant on precipitation and especially on temperature, and shows large fluctuations from year to year that are conditioned by seasonal patterns. Additionally, a strong altitudinal effect is observed on snow: as altitude increases and average temperature drops, there is greater precipitation and it takes increasingly the form of snow (Stone, 1992). At elevations between 1000 m and 3000 m, snow accumulates between the end of fall and the beginning of winter and melts during spring and early summer (Keller, 2003). The snowline above which extended snow fields remain throughout the year varies from 2400 m to 3400 m in the Swiss Alps (Stone, 1992). In mountains outside of the Alps proper, snow does not exhibit any perennial snow- covered area but in the upper parts of the Jura mountains, for example, that culminate in the Swiss part of the range at 1679 m (Mont Tendre), there are nevertheless many winter days with snow on the ground.

Due to their almost west-east orientation in Switzerland and their role of barrier for atmospheric circulations, the ridge of the Alps exhibits a pronounced contrast between northern and southern slopes in terms of precipitation and hence of snow cover (Barry, 2001). Snow patterns on each side of the Alpine chain do not present many similarities and the trends in snow depth or duration cannot be easily compared. As a consequence, chapters 2 and 3 of this research only examine selected regions of the northern part of the Swiss Alps, together with areas of the Jura chain. Large regional and altitudinal variations in snow within these mountains have already been observed by Laternser and Schneebeli (2003) over the last century. The authors broadly found that high altitudes showed only

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slight changes whereas the trends became more pronounced at mid and low altitudes: a gradual increase in mean snow depth, duration of snow cover and number of snowfall days is seen until the early 1980s followed by a marked decrease towards the end of the 20^th century. In the 1990s, a low level of snow was attained as never reached before during the last century. Scherrer and Appenzeller (2004) pointed out that this decrease could mainly be attributed to an increase in seasonal mean temperature whereas amount in precipitation did not affect this evolution in a substantial manner. These anomalously warm winters can be explained, at least in part, by the presence of very persistent high pressure episodes, induced by a positive and high North Atlantic Oscillation index (NAO) (Beniston, 1997). This large-scale climatic forcing strongly influences the surface pressure field and is amplified in the Alpine region. As a result, the low to medium elevation sites have encountered little snow and high melting rates during this period while above the range 1500-2000 m, the snowpack is much less sensitive to such atmospheric shifts.

This does not mean that snow-abundant winters have not occurred in recent years. For instance, the largest snow height ever measured in Switzerland by the national weather service (MeteoSwiss) corresponds to 816 cm at the high-elevation Säntis station located at 2502 m above sea-level, and was recorded in 1999. However, these particular events are the result of unusual weather situations, as described in Chapter 3. Therefore, the observed general trend of snow-deficient winters is rather likely to be reinforced in the forthcoming decades due to projected climate change. In this perspective, the threat for Swiss ski resorts is expected to be enhanced. As mentioned before, winter tourism in Swiss mountain areas is a major economic resource and has generally become a necessary income for local residents in addition to agriculture. Earnings of cableway companies have decreased by 20% in the late 1980s due to significant snow shortages (Becken and Hay, 2007). Snow- reliability (amount and duration) is thus definitely a key element for the ski industry. As a matter of fact, the long-term survival of cableway companies, disregarding the various economic situations of individual firms, depends on the frequency and regularity of winters with good snow conditions (Bürki et al., 2005). It is usually accepted that a ski resort can operate with profit if, in 7 out of 10 winters, there are at least 100 days of snow on the ground with a depth of at least 30 cm between December 1 to April 15 (Koenig and Abegg, 1997). On closer inspection, a large variety of ski areas coexists in Switzerland, in terms of infrastructure. This fact leads to the determination of a critical altitude beyond which snow is required for the ski lifts to run (Figure 1.2, see also Chapter 2). Furthermore, regional climatic conditions, topography, the exposure of ski slopes to solar radiation, ground texture and the use of artificial snow modulates the concept of snow-reliability for a given ski resort (Gonseth, 2008).

At the end of the 20^th century, 85% of all 230 Swiss ski regions were considered as naturally snow-reliable (Bürki et al., 2005). Snow being obviously the backbone of winter tourism, there is no doubt that climate warming is going to jeopardize considerably the financial situation of many Swiss ski areas. In this context, snow patterns in selected ski resorts in each of the main mountain regions of the country will be analysed in Chapter 2. It is also of interest to investigate whether snow-abundant winters in the long-term could still occur even in a much warmer climate, giving thus the opportunity on an occasional basis to alleviate the economic pressures on the ski industry (Chapter 3).

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UPPER RUNS

CRITICAL ALTITUDE AVERAGE ALTITUDE

LOWER RUNS

Figure 1.2. Schematic ski resort: the upper runs correspond to the top of the resort, the critical altitude to the level beyond which the snow is required for the ski lifts to run and the lower runs to the bottom of the resort. The average altitude is the mean of the three altitudes.

1.2. Hydrology of the Swiss Alps – the Grande Dixence watershed

Aschwanden and Weingartner (1985) have classified the Swiss hydrological regimes in three main classes: Alpine, Midland-Jura and Southern Alpine. The first one is characterized by an important contribution of snow and glacier melt that influences runoff seasonality. In Alpine basins, runoff generally reaches a maximum in the spring and summer, when winter precipitation locked as snow or ice is released (Westaway, 2000; Birsan et al., 2005). It is also during summer months that evaporation, which is a function of temperature and water availability, reaches a maximum (Beniston, 2004). Furthermore, the amplitude of the monthly flows in alpine areas is high between the low flows and the high flows (Horton et al., 2005) and runoff is as much as three to four times higher than in the rest of Europe (Weingartner et al., 2009). This is due to low evapotranspiration rates related to relatively low mean temperatures in such regions and due to much greater precipitation induced by orographic mechanisms. Isolated but sharp peaks in runoff are another specificity of alpine regime: strong precipitation events or rapid snow melt during sudden warming episodes can significantly enhance normal runoff in a brief period of time, potentially resulting in flooding (Schär et al., 1998).

The Alps play a major role in the hydrological regime of the Swiss and international river network (Horton et al., 2005). Surface runoff from the alpine area feeds river systems that flow into the North Sea (Rhine river basin), the Mediterranean (Rhone river basin, with about 18% of Swiss water exports), the Adriatic (Ticino basin) and the Black Sea (Inn basin) (Beniston, 2004). The vast majority of the Swiss rivers are controlled streamflows allowing flood protection, irrigation and especially electric power generation. Water power represents 56% of the Swiss electricity generation (OcCC/ProClim, 2007) and the Canton of Valais accounts for over two-thirds of the total hydroelectric generation in the country. There are indeed nine major storage hydropower dams built on tributaries within the Rhone River watershed. One of them is the Grande Dixence gravity dam that remains to date the highest of its kind in the world.

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About 400 million m³ of water is stored each year in the Lac des Dix, retained by the Grande Dixence wall. The latter was built between 1950 and 1966 and is placed at the heart of a 357 km² catchment area, half of which is covered by 35 glaciers (Luqué, 2010) (Figure 1.3).

The lake does not only collect water from its tributaries but also from other valleys, thanks to a complex system of supply tunnels over 100 km long. This hydropower facility produces an annual mean of 2100 GWh, which represents a fifth of Swiss storable energy. More electricity is produced in winter when the demand is high and when the water stored in the reservoir during the summer can be released.

As the multiple outlets that drain the Grande Dixence area are mainly dependant on pro- glacial and snow-fed rivers, the watershed is also particularly sensitive to climate change.

From a general perspective, a reduction of the amplitude between summer and winter discharge is indeed expected as larger amounts of water will run off in winter and spring, whereas summer discharge will be reduced (Horton et al., 2005). On a smaller scale, the contributions of each sub-basin will be modified and require a closer investigation. The Findelen sub-catchment area, on the East side of the watershed of the Grande Dixence, will therefore serve as a case study in chapters 4 and 5.

1.3. Modelling – methodology

1.3.1. Modelling climate

The increasing role of computer science during the 20th century has enabled the emergence of general atmospheric simulations of the earth, giving the opportunity of a better understanding of climate systems. The interactions between atmospheric, oceanic, cryospheric and biological processes must be taken into account when analysing the climate and this complexity can only be apprehended by numerical modelling. Global Climate Models (GCMs) have the ability of representing not only the past and current climate but also providing a means of testing hypotheses and theories concerning changes of future climate, thus constituting useful tools for policy analysis (Thorpe, 2005; IPCC, 2007). Nowadays, GCMs have become particularly sophisticated and can take into account sea ice component, the carbon cycle, ice sheet dynamics or even atmospheric chemistry for instance. However, in order to limit the computational demand of GCMs but preserve the most important climate properties at the highest affordable spatial or time scale resolution (typically 110 km to 500 km of horizontal resolution and 10 to 30 vertical layers, IPCC, 2007) simplifications to the full model interactive physics are unavoidable (Goosse et al., 2011). As a consequence, physical processes that are too small – such as those related to clouds or to complex topography – or operate on time scales too fast to be resolved on the grid cannot be properly modelled (IPCC-TGICA, 2007; Im et al., 2009). To avoid eliminating such important mechanisms, subgrid-scale parameterization schemes are used, that attempt to include unresolved motions and processes over circumscribed regions in a simplified, but physically-coherent manner. Cirrus and stratus cloud formation and dissipation, cumulus convection and turbulence and subgrid-scale mixing are but a few examples of parametric schemes commonly employed in GCMs (CCSP, 2008).

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Findelen sub-watershed Lake Dix reservoir Glacier

Power station Catching point Headrace tunnel

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Figure 1.3. General scheme of the Grande Dixence hydropower complex.

In addition, GCMs also provide initial and lateral boundary conditions to drive Regional Climate Models (RCMs). RCMs constitute dynamical downscaling tools that can increase the resolution of GCMs over a limited area of interest, with more detailed physical formulations, and indeed are sometimes referred to as “intelligent interpolators”. Hence, complex topographic features which strongly modulate the climate can be better taken into account by such models (Déqué, 2004; CCSP, 2008). The range of spatial resolution of RCMs is generally from 10 to 50 km and simulations are undertaken for several decades, mostly 20 to 30 years. RCMs are not an alternative to global high resolution modelling but a necessary complement (Giorgi, 2006).

At the other end of the model resolution spectrum, simulations of the climate dynamics can be generated by local models. Such models allow one to explore the potential sensitivity of the climate to a particular process over a wide range of parameters and a limited spatial extent (IPCC, 2001). Such models include the surface energy balance model or the hydrological model that have been used in the following chapters. Both of them are described further on in this chapter.

1.3.2. Modelling climate change

1.3.2.1. Natural and anthropogenic greenhouse effect

Without the natural greenhouse effect, life as we know would not exist as the mean global temperature would approach -18 °C. Instead of that, the average surface temperature is currently around 15 °C. This is due to the presence of t he atmosphere that traps a part of

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the solar radiant energy. As explained by Schneider (1992) and the IPCC (2007) for instance, particles and gases in the Earth’s atmosphere absorb about 25% of this incoming energy, Earth’s surface about 45% and the remaining part is reflected directly back to space. To maintain the energetic equilibrium, the solar radiation that is absorbed by the Earth-atmosphere system must be balanced by an equal amount of outgoing radiant energy, without which the temperature of the planet would be modified. However, according to Wien’s Law, since the Earth is much colder than the Sun, it emits radiation at longer wavelengths, primarily in the infrared region of the spectrum. The consequence is that the Earth’s surface emits thermal radiation which are absorbed by a number of trace gases within the atmosphere and reradiated both up to space and back down to the Earth. The largest contributor to the natural greenhouse forcing in the atmosphere is water vapour, followed by carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). Should the amount of a GHG be increased, it would then intercept a larger fraction of the infrared energy coming upward from the surface and thus enhance the natural greenhouse forcing.

Since the pre-industrial era, a large alteration of the energy balance of the climate system has been actually observed, induced primarily by enhanced anthropogenic CO2 emissions caused by the burning of fossil fuels. The presence of water vapor in the atmosphere is indeed not believed to be affected by human activity by far in the same proportion as CO2

(Willett et al., 2007). As a result, global average CO2 concentrations have increased from 280 ppm in 1750 to 388.5 ppm in 2010 (Conway and Tans, 2010). At the same time, the observed global average temperatures have increased by about 0.74 °C between 1906 and 2005 (IPCC, 2007). The increasing concentration of other human-induced GHGs and pollutants in the atmosphere also contribute to global warming but to a lesser extent.

1.3.2.2. Emissions scenarios

The build-up of natural and anthropogenic GHGs in the atmosphere is the primary cause for concern related to global warming over coming decades. There are, however, large uncertainties inherent to the future course of climate, linked to insufficient understanding of complex, non-linear mechanisms between elements of the climate system, data gaps and insufficient data (Nakicenovic, 2000). Moreover, in order to anticipate changes in climate, it is necessary to take into account not only the physics of the system but also a wide range of the numerous driving forces of future emissions, that range from demographic to societal systems, including technological change and economic growth (IPCC, 2000). In this perspective, the Intergovernmental Panel on Climate Change published a Special Report on Emissions Scenario (SRES, IPCC 2000) where a set of alternative emissions projections are developed, each of which can be considered as representative of possible emission futures. Thus, 40 different SRES scenarios encompass most of the GHG emissions range in the published scenario literature and are intended to serve the scientific community in assessing climate change impacts. It should be noted however that they do not include any explicit policies directed at reducing GHG sources or enhancing sinks. The set of scenarios is rather inclined at providing a benchmark for the evaluation of mitigation and adaptation measures, as well as climate policy interventions.

The 40 SRES scenarios are grouped into four alternative scenario families or “storylines”

(A1, A2, B1 and B2) in an attempt to define a manageable and relative small number of projections. They represent nevertheless a wide range of possible futures and yet avoid the

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impression that there is a central or most likely case. Each of the four storylines includes a demographic, politico-economic, societal and technological future associated with global and regional developments and their implications for GHG emissions. Within each family one or several particular scenarios were selected to serve as “prototypes” that can particularly well illustrate the entire set. In this study, only the SRES A2 scenario is applied on snow and runoff data. This A2 experiment gives a relatively strong climate change signal compared to the other scenarios. According to the IPCC (2000), it describes a very heterogeneous world. The underlying theme is the strengthening of regionally oriented economic growth with an emphasis on family values and local traditions, a continuously increasing global population, less concern for rapid economic development and low priorities on GHG abatement strategies. Concerning the repercussions on emissions values, this scenario projects a high level of CO2 concentrations of about 800 ppm by 2100, i.e.

about three times their pre-industrial values. In the following chapters the selection of a unique scenario should not be considered as limitative since the overall goal of the present study is to establish methodologies on how snow and runoff may be modified in an enhanced greenhouse climate. Besides, the SRES A2 scenario, standing in the upper bound of estimates of climate futures, is likely to lead to severe outcomes. It has thus the advantage of preparing stakeholders concerned by such issues to one of the strongest responses to GHG forcing; any other emissions scenario would presumably lead to less severe impacts.

1.3.2.3. PRUDENCE project

To better evaluate climate change at the Europe level driven by SRES scenarios, the Prediction of Regional scenarios and Uncertainties for Defining European Climate change risks and Effects (PRUDENCE) project was carried out from 2001 to 2005 (Christensen, 2005). It involved more than 20 European research groups with the common objective of assessing general trends of climate change scenarios for Europe at the end of the 21^st century with dynamically downscaled high-resolution models. A further objective of PRUDENCE was to explore the uncertainty in these projections (Déqué, 2004; IPCC, 2007).

The results of such analyses have the advantage of justifying the use of simulations from one RCM experiment only. Indeed, the outputs of the HIRHAM RCM of the Danish Meteorological Institute (Christensen et al., 1998) correspond well with those of the other RCMs used in PRUDENCE and are located mostly in the middle of the range of simulations for most geographical regions, climate variables, and seasons (Christensen and Christensen, 2007). The HIRHAM model has therefore been chosen in this study in order to evaluate the physical impacts of climate change on snow and runoff. This RCM has a horizontal resolution of 50 km, in which Switzerland is covered by 21 grid points. Among the many fields archived in HIRHAM, only daily values of air temperature, precipitation and dew point temperature were used in this research. During the duration of the PRUDENCE project, this RCM completed both a control simulation to reproduce the baseline climate period from 1961 to 1990, and a future scenario simulation – the greenhouse climate – representing the period from 2071 to 2100. For the A2 scenario, simulations have used the boundary data from the Hadley Centre Atmospheric Model HadAM3H GCM to provide a detailed understanding of the regional model uncertainty (Pope et al., 2000; IPCC, 2007).

Again, the use of one rather than an ensemble of RCM outputs should not be viewed as restrictive, as the HIRHAM has in the past proven to be reasonably accurate in mountain

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regions (Beniston et al., 2010). To apply the climate projection of the selected RCM to the physical features of snow and runoff, two different approaches of the so-called “delta downscaling method” were used. These are described in detail in chapters 2 and 5 and comparison of both methods is to be found in Appendix C.

1.3.3. Modelling snow 1.3.3.1. Modelling snow patterns

The use of fine-scale snow cover modelling is essential as snow patterns cannot be totally captured by RCMs simulations due to very varying local atmospheric conditions in mountain areas. Scattered meteorological measurements in such environments constitute another difficulty. In addition, the energy aspects linked to snow melt processes require an accurate treatment of the thermodynamics of the snow pack (Keller, 2003). Downscaling techniques or snow models can achieve this aim; a physically based Surface Energy Balance Model (SEBM) is another option to serve this purpose and has been selected in chapter 2. A SEBM is a simplified physically-based representation of the climate system, based on the simulation of the temporal evolution of the radiative, energetic and hydrological budgets, determined by boundary conditions. Results are valid at a given location, in response to these specific local atmospheric states. In addition snow patterns are well described by equations taking into account energy and water fluxes between the Earth’s surface and the atmosphere (Gustafsson et al., 2001; Keller, 2003).

GRENBLS (GRound ENergy Balance for naturaL Surfaces) is the model used in this study.

It is a semi-prognostic model driven by hourly datasets that can be provided either by meteorological observations or in the present case by archives of an RCM. The model computes solar and infrared radiative fluxes, turbulent fluxes of sensible and latent heat, as well as the heat flux in the ground and within the snow pack. Precipitation determines the amount of snow that falls when temperature drops below 0 °C and liquid precipitation falling on the snow pack induces snowmelt. The snow pack is modelled as a unique but evolving layer characterized by a temperature, a mass and a density. Except for heat flux, the internal processes within the snow cover are hence not represented in the model. The snow temperature is obtained in a semi-prognostic manner from the energy budget of the pack.

Runoff results from the bottom drainage and soil saturation. The melting snow directly enters the underlying surface and contributes to the soil moisture equilibrium (Keller, 2003;

Keller and Goyette, 2005). A more comprehensive model formulation and upgrades can be found in Appendix A.

Consequently, such model is a useful tool that can give a reasonable overview of snow patterns at a fine scale in the Swiss mountains. With climatic (i.e. long-term) forcing, it has the ability of assessing the sensitivity of the snow pack and winter season to shifts in temperature, precipitation and humidity.

1.3.3.2. Variability of winter snow conditions

GRENBLS is a valuable model for determining snow patterns but cannot give direct indications on the variability of winter different snow conditions. It has been seen that a few snow-abundant situations have been experienced in recent years, despite an increase in

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temperatures in many parts of the Alpine domain. It is thus of interest to investigate whether snow-abundant winters could still occur in an enhanced greenhouse climate.

The snow amount and duration of a season is clearly dependant on particular synoptic circulations. The latter can be assessed by a statistical technique: the joint probability temperature/precipitation distributions that represent reasonable proxies for weather patterns and persistence (Beniston and Goyette, 2007; Beniston, 2009). In this perspective, the 25% and 75% joint quantiles were used to define winter situations that are cold/dry, cold/wet, warm/dry and warm/wet. This methodology enables to extract the weather mode that has currently the strongest influence on snow and to examine whether this particular mode would still arise in an enhanced greenhouse climate.

1.3.4. Modelling runoff

As GRENBLS also describes the evolution of the water budget at a specific location, it could have been used in chapters 4 and 5. However, a hydrological model that can address the overall issues related to water (together with snow and ice) and that is designed especially for drainage surfaces seemed more appropriate. Among the numerous existing hydrological models, a conceptual model named Routing System 3 (RS3.0) was chosen. It is particularly well conceived to represent in an accurate manner the hydrological routines linked to temperature and melting processes as it is essential in the cryosphere. Besides, not only can the model reproduce particular events but it can also be applied to continuous multi- annual simulations (Hernández et al., 2007). The selection of RS3.0 was also determined by the possibility of modelling natural and artificial elements at the same time. Indeed, hydroelectric installations, such as turbines, storage reservoirs, pumps or river water intakes for instance, can be implemented in the model. The civil engineering orientation of RS3.0 thus provides the opportunity of future developments towards the modelling of the entire Grande Dixence watershed, including hydraulic infrastructures. Energy and economic impact studies could therefore easily be achieved and could definitely bring a valuable asset to this research topic.

RS3.0 is composed of four sub-models that are described in chapter 4 and more thoroughly in Appendix B. Snow and ice sub-models use a degree-day approach. Such a method is fairly simple to implement, has few data input requirements and shows good performance in terms of accuracy. In addition, a parameterization of some characteristics of the glacier (such as ice velocity or mass transfer downstream) is incorporated in the ice sub-model.

Runoff and infiltration sub-models are implemented through a conceptual model (an extension of the GSM-SOCONT model, described by Schaefli et al., 2005). For ice-covered areas, mass conservation is respected, the snow mass is transferred to the ice mass and the gravity flow of the glacier is integrated in the sub-model definitions. For areas not covered by ice, the equivalent precipitation composed of snow melt and precipitation is transformed into runoff through two reservoirs: a linear one for the slow contribution of soil and underground water and a non-linear one for direct or quick runoff. Consequently, this conceptual methodology in RS3.0 enables an analysis of the components of runoff in order to achieve a realistic water balance in the catchment area.

This hydrological model has shown good skill at reproducing observed runoff in a highly glacierized catchment in the Alps. With stochastic generated weather data as input, RS3.0 was capable of evaluating the response of runoff to a stabilizing climate over more than one

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hundred years (i.e. if the current observed warming trends were to cease) and highlighting the role of glaciers that are out of balance with respect to atmospheric conditions. Similarly with climate change, discharge trends and glacier evolution have been projected to the end of the century. Discharge series both of the artificially stable and perturbed climates are compared in Appendix D.

1.4. Implications for mitigation and adaptation strategies

The analyses that are developed in the next chapters evaluate the physical impacts of climate change on snow and runoff. The expected results will inevitably force a profound mutation of the ski industry and the hydropower management. An important mitigation potential in Switzerland, consisting in reducing GHG emissions, exists and is determined by the rigor of the political constraints (i.e. by normative policies) and by the pace of technological development (OcCC, 2008). Mitigation would also include, in the case of winter tourism, reducing emissions in relation to both activities at the ski fields and to transportation systems themselves that connect to ski fields (Becken and Hay, 2007).

However, adaptation strategies are globally still prevailing (Elsasser and Messerly, 2001).

Changes are also expected on the demand-side for ski tourism as unfavourable snow conditions may prevail in the future (Koenig and Abegg, 1997) but are rarely taken into account in vulnerability assessments. Climate change adaptation in the ski industry is anticipated to remain largely individualistic as well (Scott and McBoyle, 2007) but measures to counter the increasing potential for snow scarcity in ski areas follow nevertheless three main orientations: the attenuation of the signal, the diversification of the leisure activities and a partial or total reorientation of tourism (OcCC/ProClim, 2007). One of the best known measures in relation with the first orientation is the investments in artificial snow making facilities. However, such installations have growing limitations with a warming climate, including disproportionately larger and larger investments, operational and exploitation costs, ecological impacts or water availability (De Jong et al., 2008; OECD, 2006). Besides in this domain, many ski companies are even in present day conditions dependant on the financial support by local authorities (Gonseth, 2008). Such options should thus be considered as a palliative response to deteriorating snow conditions as it will sooner or later become unsustainable. The diversification of the leisure activities seems more appropriate to such an issue. For example, the drier and warmer mountain summer months may offer more mountaineering and hiking opportunities that could partially compensate for reduced skiing (Beniston, 2003). A new range of recreation activities may also emerge with longer summer seasons (Becken and Hay, 2007, Hoy et al., 2011). The last orientation concerns resorts whose skiing future is far more in economic danger. The development of wellness spas or summer bob slides for instance could assure a financial viability for resorts where snow can no longer be guaranteed, which implies a complete reorientation of marketing strategies towards snow-independent winter tourism.

The mitigation and adaptation measures to cope with climate change on hydropower facilities are more ambiguous. Hydropower indeed represents a mitigation measure in itself to reduce GHG emissions as it is the only major renewable energy source contributing to electricity supply (Harrison and Whittington, 2001). But at the same time hydropower

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production patterns will paradoxically suffer from climate change and will therefore have to take adaptation actions. As a consequence, reciprocal repercussions and possible conflict between mitigation and adaptation might arise over hydroelectric generation (Bates et al., 2008).

Hence in the future, less water will be available for hydroelectric production whereas an inevitable increase in energy consumption is expected. To face this challenge, new hydroelectric facilities are still likely to be developed to reduce dependence on fossil-fuel energy sources (OcCC/ProClim, 2007) since hydropower has an extremely high earning ratio: it can produce 150 to 250 times as much energy as is needed for the construction and operation of the plant (Hauenstein, 2005). In the context of energy stress, other environmental issues may arise as well, such as potential modifications of flood intensity and frequency or increasing sediment loads in rivers, resulting from permafrost degradation.

Adjustments of existing infrastructures will thus have to be implemented as well. In this perspective and to avoid undesirable feedback mechanism, solutions should not be initiated without the integration of climate change into planning processes (Beniston et al., 2011).

These mountain-specific challenges in the framework of climate change would not be possible without a thorough analysis of snow and runoff patterns. The studies presented in the next chapters intend to provide some physical basis for further indirect assessments of global warming on tourism and hydropower production.

Modelling snow and runoff patterns in Swiss mountain environments under conditions of climate change

Thesis

Reference

Modelling snow and runoff patterns in Swiss mountain environments under conditions of climate change

UHLMANN-SCHNEITER, Bastienne

Abstract

UHLMANN-SCHNEITER, Bastienne. Modelling snow and runoff patterns in Swiss

mountain environments under conditions of climate change . Thèse de doctorat : Univ.

Genève, 2011, no. Sc. 4388

URN : urn:nbn:ch:unige-184870

DOI : 10.13097/archive-ouverte/unige:18487

Available at:

http://archive-ouverte.unige.ch/unige:18487

Modelling Snow and Runoff Patterns in Swiss Mountain Environments Under Conditions

of Climate Change

THÈSE

Remerciements

Contents

Résumé

Abstract

Chapter 1

Overall Introduction

1.1. Snow cover in Swiss mountains and tourism

1.2. Hydrology of the Swiss Alps – the Grande Dixence watershed

1.3. Modelling – methodology

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1.4. Implications for mitigation and adaptation strategies