The application of a groundwater/surface-water model to test the vulnerability of Bracciano Lake (near Rome, Italy) to climatic and water-use stresses [Utilisation d’un modèle eau souterraine/eau de surface pour tester la vulnérabilité du lac Bracciano (près de Rome, Italie) à la pression climatique et d’usage de l’eau] [Aplicação de um modelo de águas subterrâneas/superficiais para testar a vulnerabilidade do Lago Bracciano (perto de Roma, Itália) a estresses climáticos e de uso de água] [Aplicación de un modelo agua subterránea/agua superficial para testear la vulnerabilidad del lago Bracciano (cerca de Roma, Italia) a estreses climáticos y del uso del agua]

Modelling tools are necessary for quantitative assessment of groundwater-dependent systems such as interacting groundwater aquifers and lakes. Numerical groundwater models supplemented by stream and lake submodels are the best available tools for testing the conceptual relation of surface water to groundwater, for identifying gaps in the amount and quality of data, and for better understanding the sustainability of a groundwater-lake system in the presence of stresses. Models are of particular interest when applied to an infrequently studied geological context that is subject to specific vulnerabilities and patterns of interaction. Volcanic lakes are one setting where flow models serve to extend current conceptual and practical understanding. In this study, a groundwater/surface-water flow model is presented for the flow-through Bracciano deep caldera lake located near Rome, Italy. The steady-state model quantifies and tests the existing conceptual understanding of the system by taking account of all sources and sinks, and by calibration of key parameters to head and flow data. A transient version of the model demonstrates the response of the system to dry and wet years and to anthropogenic stresses. Although precipitation is the dominant source of water overall for the lake, a major finding of this study is that the groundwater inflow to the lake can buffer fluctuations in lake-water level and reduce lake-level declines, especially during shorter periods of dry conditions. © 2015, Springer-Verlag Berlin Heidelberg.