In light of seasonal climatic and anthropogenic changes, is the Vaud canton (Switzerland) vulnerable to water stress by the medium-term?

Abstract

Observed changes in hydrological processes during the past 20 years in Switzerland are particularly preoccupying as they directly affect water use. In 2003 and 2011, local water shortage episodes occurred. Water withdrawals and supplies had to be restricted, notably in the Vaud canton (Western Switzerland). These droughts highlighted increasing competition among water users and new water management issues arose. This study explores how hydro-climatic conditions and water needs could evolve by the 2060 horizon and assesses the vulnerability of the canton to water stress under climatic and anthropogenic changes. Flows were simulated based on a daily semi-distributed hydrological model. Future changes were derived from Swiss climate scenarios relying on ten regional climate models. Regarding water needs, a population growth scenario was provided by the canton whereas a business-as-usual scenario was considered for irrigation and breeding trends. Currently, catchments in the canton experience moderate water stress from June to August, except in alpine areas. By the medium-term, water needs could reach more than 80% of rivers' total runoff in July and August. This should be due to higher temperatures and a higher ratio of liquid-to-solid precipitation causing more severe low flows. In addition, water needs should significantly increase from April to July, due to higher irrigation (+25%) and urban (+40%) water needs. This study gives a first overview of where and when water tensions are most likely to occur in the Vaud canton. Highlighting these regional differences supports the development of strategies to cope with water stress that are currently being discussed with the cantonal authorities. RESUMEDans un contexte de changements climatiques et anthropiques, le canton de Vaud (Suisse) est-il vulnérable au stress hydrique ? Au cours des ces 20 dernières années, une modification des processus hydrologiques a pu être observée en Suisse. Par exemple, la limite des chutes de neiges s'est élevée de 150 m, la fonte et le recul des glaciers se sont accélérés et les épisodes de sécheresse se sont intensifiés en été. Ces changements sont particulièrement préoccupants, d'autant plus qu'ils affectent directement la disponibilité des ressources en eau et l'approvisionnement en eau des différents usagers. En 2003 et 2011, la Suisse a dû faire face à des épisodes de pénurie d'eau au printemps et en été, provoquant des restrictions d'usages de l'eau à plusieurs reprises, notamment dans le canton de Vaud (Suisse occidentale). Ces épisodes ont révélé des compétitions accrues entre usagers ainsi que de nouveaux enjeux en matière de gestion de l'eau, tel que la définition de priorités et de taux d'allocation en eau entre les différents secteurs d'activités. Ainsi, cette 1 Corresponding author: Marianne Milano Congrès SHF : «Water Tensions in Europe and in the Mediterranean: water crisis by 2050? October, 8-9 2015, Paris-Marne la Vallée »étude tente d'identifier comment les conditions hydro-climatiques et les besoins en eau pourraient év...

Droughts in forested ecoregions in cold and continental climates: A review of vulnerability concepts and factors in socio‐hydrological systems

“…As some of the reviewed literature on sub-national scales focused on agriculture in semi-arid climates, access to irrigation as a factor in assessments of vulnerability is further explained. At the same time, as was exemplified by Milano et al (2016), irrigation can be seen as a factor that may lower vulnerability in agriculture, while irrigation water needs can raise the vulnerability of water resources to water stress. Therefore, when using irrigation as a factor for assessing drought vulnerability, it is important to clearly establish the focus of the study, or to acknowledge the paradoxal nature of irrigation in the vulnerability analysis.…”

“…Among articles focusing on water resources and supply (Figure 5), as well as articles having a holistic perspective, factors concerning water availability were among the most frequently used. For instance, water stress was included in six out of eight articles looking at vulnerability in water resources and supply systems, where most expressed it by using indices such as water depletion indices (Ahopelto et al, 2019), water stress indices (Milano et al, 2016), or groundwater exploitation indices (Gurwin, 2014; Minea et al, 2020; Schumann, 1997). This factor was also mentioned in connection to other sectors.…”

“…For instance, access to irrigation is regularly used as a factor decreasing drought vulnerability in agriculture (e.g., Buzasi et al, 2021; Wittrock et al, 2011). Meanwhile, in articles assessing drought vulnerability using indices related to water stress and competing interests, irrigation is sometimes included as a factor that increases vulnerability by adding pressure on water sources used by several competing interests (Milano et al, 2016). Furthermore, as irrigation requirements during drought can exceed water availability (Ahopelto et al, 2019; Wheaton et al, 2008) or water allocation permits (Hurlbert & Montana, 2015; Neilsen et al, 2018), the potential of its performance as a factor lowering vulnerability may be dependent on surrounding circumstances as well.…”

Why do we have so many different hydrological models? A review based on the case of Switzerland

“…We further discuss such land-use change studies in Section 2.2.3. Overall, catchment-scale ecohydrological studies remain rare in Switzerland, a situation that might change due to increasing awareness of human pressure on natural ecosystems and potential water use conflicts (Milano et al, 2016).…”