This paper presents a new methodology for the zoning of littoral sand barriers on the basis of their groundwater dynamic responses to the local mean water level (MWL) climate. The method is based on the comparison of the characteristic scales of the horizontal drainage and recharge processes. Using the Boussinesq equation and basic hydro-geomorphological parameters, this methodology identifies the climatic events that markedly affect the groundwater dynamics across the barrier, along with the location of the most affected cross sections. The application of the methodology to the Mar Menor sand barrier shows that a significant number of cross sections can be particularly vulnerable to the effects of local storm events typical of the Mediterranean coast during the spring and winter seasons. The location of the affected cross sections is analyzed as a function of both the local MWL forcing and hydrogeological parameters. This case study highlights the possible use of the proposed methodology for land use planning and the environmental management of coastal sand bars.