Dévoluy is a mountain range located in the southern French Alps. It is the last foreland chain before the outer crystalline Pelvoux massif. The carbonate rocks that constitute it form a reservoir of several hundred meters thick, folded and fractured by Alpine orogeny during the Cenozoic. This reservoir, exposed to erosion, was then intensively karstified, creating a network of interconnected karstic conduits leading to a unique outlet: the Gillardes spring. This is one of the most important karstic resurgences in south-eastern France, with a peak discharge that can reach 40m3/s and an average of 5m3/s. Due to its position in the Southern Alps, a geographical area subject to increasing water stress in the context of climate change, the Dévoluy massif presents a major challenge in understanding and preserving the local groundwater reserves. It is located in an area where anthropic needs a represented by two main activities : agriculture and tourism with ski resort. It is essential to better constrain the underground water resourcesto protect it from potential pollution and to use it in a sustainable way. The aim of this study is to provide an overall analysis of the evolution of the karstic reservoir, from its formation to its current state, by analysing each of its components. This section of the study focuses on modelling the dynamic of the karstic reservoir. The data used are the discharge measured at the outlet and the weather conditions: temperature and precipitation from various stations located in and around the massif. The impact of snow is also taken into account, as the case study is located in a mountainous area. The model enables us to understand how the different compartments of the reservoir can affect the flow at the outlet and is a way of better understanding the structure of the karstic reservoir: is there one or more compartments, how do they interact with each other, what is the response of the aquifer to precipitations. This model can then be used to predict future flow in different scenarios based on climate change projections. These scenarios make it possible to test hypotheses on changes in precipitation and temperature in order to assess the impact of these changes on the behaviour of the reservoir.