Exploration of water management adaptation strategies in the context of climatic changes in the Alps using a modelling tool

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1 Exploration of water management adaptation strategies in the context of climatic changes in the Alps using a modelling tool Eve Leroy 1 and Georges-Marie Saulnier 1 1 University of Savoie, EDYTEM laboratory, Le Bourget du Lac, France ABSTRACT : In the Alps, various studies conclude to a significant temperatures increase and a less clear signal for precipitation. Nevertheless, more solid precipitation is expected to become liquid due to the winter temperatures increase. As a result, hydrological regimes of mountainous territories are evolving. Business Models directly or indirectly linked with water availability will be then impacted by the hydrosystem evolution (e.g. drinking water, hydroelectricity, agriculture, industries, tourisme, etc.). Alpine regions should care about future water availability, i.e. to adapt in order to prevent water uses conflicts and to sustain its socio-economy. To help the Alpine community to face these issues, we improved hydro-meteorological models by coupling them with water resources management and socio-economic modules to explore different development strategies and to evaluate their effect on the water resources in the context of climatic changes. This works is funded by the Alpine Space C3-Alps project 1. To explore adaptation strategies to climatic changes in the water management sector, both climatic and socio-economic dimensions have to be represented as they are key drivers of the water resources sustainable use. A first model combining socio-economic and climatic scenarios was built for the Megève ski resort (France). Hydrological processes are represented as well as anthropogenic withdrawals. Effect of different climatic scenarios and anthropogenic activities on the water resources availability can be quantified. The model is used to help decision makers when designing reasonable development strategies taking into account future climates and human policies. KEYSWORDS : Water management, climate change adaptation, development strategies, Alpine Space 1 INTRODUCTION Most human activities highly depend on water availability. Interactions between the hydrological environment and the human activities are perpetual and work both ways. Water is withdrawn from the environment to be used for human needs and to be transformed for economic use. This impacts the quantity and quality of water bodies and consequently has implication in both short and long terms on the water resources availability for economic uses (Brouwer and Hofkes, 2008). The socioeconomic development of a territory depending on water availability is therefore constrained by two main drivers. Firstly, the hydrosystem sensitivity to climate firstly depending on precipitation and temperature conditions, impacts the amount of water available in the environment for all the activities depending on water availability. Secondly, socio-economic withdrawals and territorial policies (e.g. minimal flow, land uses etc.) impact the water sharing capacity and therefore the territorial potential development. The main drivers are subjected to changes. The Alpine territory well illustrates these changes. 1 The Alps face important climatic changes with a higher sensitivity to temperature increase (Auer et al., 2007) which impacts the mountainous hydrosystems. In the same time, economical models of the Alpine Space are impacted by the hydrosystem evolution (European Environmental Agency, 2009) with activities highly depending of the quantity of snow (winter tourism) and based on the multifonctionnality of the water resources (hydroelectricity, households, industry etc.). There is a need to understand the links between the hydrosystem sensitivity and socio-economic development in this area. This would help to develop strategies corresponding to current and future water availability in order to prevent water crisis in the Alps and to promote a sustainable development. This is the goal of the model developed on the Megève ski resort territory (France) and the Savoy department with the help of the C3-Alps project. In this paper we present the modelling tool develop in focusing on the Megève pilot area. 1273

2 2 MEGEVE PILOT AREA Megève is a ski resort municipality located in the French Alps. The Megève name meaning between two waters in local dialect comes from its geographical position in a pass between the Arly watershed and the Arbon watershed. Thus the municipality is in a central position to withdraw water but also have a main role in the water management of the Arly river. Megève does not significantly suffer droughts as the average precipitation is 1,464 mm per year. Nevertheless, many activities depend on hydrosystem services (e.g. drinking water supply, tourism, snow production, hydropower, agriculture, etc.). The risk of water scarcity is then real, especially during the winter season when the population is multiplied by ten in the mean time of the low water period A municipality involved in the European water management research Aware of the link between the economy of ski resort station and the water resources evolution, some projects have been carried on the Megève territory. The first Interreg Alpine Space project Alp-Water-Scarce aimed to build an early warning system to prevent water scarcity (this project ended in October 2011). This project helped in building a monitoring system of the Megeve catchment. This system surveys in real time hydrological conditions (precipitation, temperature, water conductivity, water tables, etc.). This monitoring enables a good estimation of the different variables implied in the water balance. An hydrological model was built which contributes to an improved understanding of the hydrosystem's functioning, resulting in a reliable, consistent and well constrained representation (Hohenwallner et al; 2011). This model was used as a basis for this research. The C3-Alps project, funding by the Alpine Space Programme started in 2012 and aims to capitalise previous knowledge on climate change adaptation into concrete actions. Two pilot areas are located in France : the Savoy department and the Megève municipality. In the case of Megève pilot area, the results of Alp- Water-Scarce project are capitalised to go a step further and implemented concrete water management adaptation. The municipality decision-makers and stakeholders are involved in the project and act directly especially on socio-economics aspects. 2.2 Climate change on the Megève territory Megève has experienced as all the Alps a strong temperatures increase. The histalp homogenised temperatures representing the Alps trend since 1900 (Auer et al., 2007) and the SAFRAN temperatures recorded in the Megève area since 1960s compared to the IPCC A1B trend for Europe (figure 1) show a clear temperature sensitivity of alpine territories to climate change. The Alps seems to warm as twice the rate of the rest of Europe. Temperature increase leads to a shorten snow period with less water storage in winter, impacting anthropogenic activities in the Alpine space. Consequences also affect downstream activities as most of the major European rivers have their headwaters in the Alps. It is therefore crucial to deal with this hydrosystem evolution and built a sustainable development taking into account actual and future climate. 3 MODELLING HYDROLOGICAL PROCESSES AND SOCIO-ECONOMIC ACTIVITIES Two main components influence the water availability for anthropogenic uses. Firstly the natural water available in the hydrosystem, depending on various parameters as temperature, precipitation, soil, topography, etc.. and secondly the socio-economic context including water withdrawals, laws, connected pipes, etc.. To define territorial development strategies, there is a need to well represent these two components in order to reflect the water resources reality. In this study, a modelling tool was built to answer this research question. We use a modular approach (figure 2) meaning that a connection is built between the hydrological model and the socio-economic model (Brouwer and Hofkes, 2008) The hydrological module The hydrological module used is this study was developed during the Alp-Water-Scarce project. By this way the capitalisation aim of the C3-Alps project is respected. It is based on the Topmodel framework (Beven and Kirby, 1979) modified to be able to study both floods risk issues (Saulnier and Le Lay, 2009) as well as water resources problems (Le Lay et al., 2008). Basically, the model predicts the soil water content spatial distribution at each time step at every DTM pixel. 1274

3 Figure 1. HistAlps and Safran temperatures and trends in the Megève area (Saulnier et al., 2011). The hydrological module built uses data from the monitoring network installed for more than 3 years and well dispatched in the Megève watershed. It allows a good consideration of the territorial reality. The model hydrological module is used to know in each point of the Megeve basin and at each time step the natural water runoff, storage, evaporation, etc. The runoff is then potentially available for anthropogenic uses, potentially withdrawn to be stocked in reservoirs or directly used (e.g. agriculture) The socio-economic module The second module of the model is the socioeconomic activities. It aims at modelling all the anthropogenic activities in the watershed and at being able to evaluate the impact of decisionmaker scenario on the water resources. The water supply system organisation is one of the components of the socio-economic module. How the supply system is organised in reservoirs, pipes and catchment areas? All the data corresponding to the water network organisation are compiled and used in the model. If some modifications occur as the construction of a new reservoir or a renovation of pipes to decrease leaks, the supply system component in the model can easily be modified as well. All the supply network characteristics were obtained thanks to the collaboration with the Megève municipality. A second component of the socio-economic module is the water consumption of anthropogenic activities. For each activity, a specific consumption is calculated at each time step (day or hour). The calculation can be done for household local and touristic populations, agriculture, snow production, hydroelectricity and each anthropogenic activity. A close relation with the municipality and the water managers of the city is required in order to insure the quality of the data and the good representation of all the anthropogenic activities. The third component of the socio-economic module gathers rules, legislations and decisions that can impact the water resources consumption. For example, the drinking water supply has the priority above all other uses and is always the first need to be satisfied. These rules are translated in algorithms within the model. Other legislations as the environmental minimal flow are also included in the model. The rules can be changed as the legislations or behaviours change. 1275

4 4 SCENARIOS DEVELOPMENT The main strength of the model organisation is to enable easy modifications of the socioeconomic components and the modification of precipitation and temperatures inputs for the hydrological module. By this way, two type of scenarios can be developed and tested in the model: climatic scenarios with the variation of precipitation and temperatures and socioeconomic scenarios with the evolution of several components like the water uses consumption or the legislation. The scenario term is used in this study to define a possible future in term of climatic conditions or socio-economic development of the area studied. It is not a prediction. Different scenarios are tested in the model in order to browse the larger possible futures. The aim is to define the possible sustainable ways to develop the Megève area in adequacy with the future water resources to avoid water crisis in the near or distant future. drivers for the water resources contain in the Megève watershed. Climatic scenarios tested are therefore based on this two parameters. Different time scales are studied for the climatic scenarios. A short term scenario (few days to a few weeks) using meteorological forecasts of the coming weeks as inputs of the precipitation and temperatures variables should help stakeholders to avoid water crisis. As an example, if the reservoirs are close to their lowest levels while tourists are hosted in the city and there is a need for snow production, it is useful to know few days in advance if precipitation would comes in order to take the adequate decision to avoid water shortage. It is the aim of the short term scenario. Medium term scenarios (few months), using climatological records and statistic should help stakeholders to define their strategies for the coming season Finally, long term climatic (few years to a few decades) scenarios using climate changes scenarios developed by climatologists, as the IPCC, should help to define local development strategies compatible with future climate conditions and especially future water resources. Fig. 2. The model organisation 4.1. Climatic scenarios Mainly constituted by surface waters runoff, temperatures and precipitation are the main 4.2. Socio-economic scenarios Socio-economic scenarios are designed with local stakeholders in order to insure consistency and interest of the modelling. The aim is to develop and test the sustainability of different development scenarios in the actual and future climatic conditions. For example, the legislation for environmental flow will likely evolves to more severe restrictions for anthropogenic withdrawals. How this new legislation will impact actual water uses? This parameter can be tested with different minimal flow thresholds in the model. With this simulation, stakeholders may design a response to this legislation evolution and adapt their actual and future consumption. For a long-term perspective, in France the decision-makers have to present a development plan for their area for the 10 to 20 coming years. The plan must represent the social, urban and economic development envisaged for the municipality. It has to take into account environment, water resources and climate vulnerability. By using the model developed in this study, different socio-economic development can be tested taking into account climatic changes scenarios and can help decision- 1276

5 makers to define a development plan for their territory. Every scenarios in different fields can be tested if sufficient data are available to insure results consistency : in agriculture (different crops, organic or intensive, irrigation, etc.), in tourism (ski tourism, four seasons tourism, highend tourism, etc.), in population (increasing population, decreasing and older population, etc.), in energy (hydroelectricity evolution with climate change), in legislation (environmental flow evolution, water saver implementation, etc.). The aim of the socio-economic scenarios is to test all the scenarios envisaged by stakeholders in order to find the best way of development for the municipality based on local data. 5. CONCLUSION Local decision-makers and stakeholders have to deal with many complex parameters to define the best ways of development for the territory they manage. Nobody can predict exactly the future climatic conditions but there are enough certainties to input the climate change parameter at the negotiating table. In mountainous area, temperature is a key variable to define the water resources amount available for anthropogenic uses. Since more than a century, the trend is to a warmer climate in the Alps. It impacts the hydrosystem functioning and through it the socio-economy of mountainous territories. The model developed in this study take into account the socio-economic dependency on water availability. By modelling the hydrosystem sensitivity to temperature and precipitation and the variability of human withdrawals, most of the main parameters of territorial development plan is included in the same tool. The effects on water resources of different climatic scenarios as well as different society development can be quantified. The tool works at three time scales corresponding to different problematic. The decision-makers can therefore support their decision on objective data and find the best development path for their territories. hydrology, Hydrological Sciences Bulletin, pp Brouwer, R.; Hofkes, M.; 2008, integrated hydroeconomic modelling : Approaches, key issues and future research directions, ecological economics, 66, pp European Environmental Agency, 2009, Regional climate change and adaptation, the Alps facing the challenge of changing water resources, 143 pp Hohenwallner, D.; Saulnier, G-M.; Castaings, W.; et al., 2011, Water Management in a changing environment strategies against water scarcity in the Alps, Alp-Water-Scarce project outcomes, 73pp. Le Lay, M.; Saulnier, G. M.; Galle, S.; Seguis, L.; Metadier, M. & Peugeot C., 2008,Model representation of the Sudananian hydrological processes: Application on the Donga catchment (Benin), Journal of Hydrology, 363, Saulnier, G. M. & Le Lay, M.; 2009, Sensitivity of flash flood simulations on the volume, the intensity and the localization of rainfall in the Cevennes-Vivarais region (France),Water Resources Research, 45, W10425 Saulnier, G-M. ; Castaings, W. ; Reszler, C. ; Hohenwallner, D. ; et al., 2011, Climatic scenarios guideline, Alp-Water-Scarce (Interreg IV B, Alpine Space Programme, project F), pp REFERENCES Auer, I; Böhm, R.; Jurkovic, A. et al., 2007, HISTALP Historical instrumental climatological surface time series of the Greater Alpine Region , International Journal of Climatology, 27, pp Beven, K.; Kirby, M.; 1979, A physically based variable contributing area model of basin 1277