Although karst aquifers represent a widespread groundwater resource in Europe, there is no unified classification and each country has adopted his own typology, taking into account the characteristics of their own karst aquifers. The main objective of the CHAKA (CHAlk and KArst) work package, part of the GeoERA RESOURCE project (http://geoera.eu/projects/resource9/), is to achieve a joint classification typology that should be applicable to a large spectrum of karstic environments, and to associate it to recommendations regarding aquifer management (aquifer protection, monitoring strategies, exploitation, etc.). This presentation describes the current state of the art, in the sense of reviewing the existing methods/approaches used in the different partner countries to classify karst aquifers taking into account the responses from time series analysis. The existing approaches of carbonate aquifer characterization are studied and the differences and complementarity of the different approaches are discussed. The potential gaps are also identified.