Climate change might affect energy production and therefore the energy security of a country or region. This vulnerability situation may affect Renewable Energy Sources (RES) such as hydroelectric and has consequences on effective energy transition. Since the transition to RES is a key for decarbonizing the economy in line with the Paris Agreement this situation is critical for many countries in which their energy systems are linked to resources strongly affected by climate. The aim of this study is to purpose a vulnerability indicator (VI) to evaluate the electric energy vulnerability of an on-grid system to climate change at national and regional level taking as base the case of study of Colombia, a country with a system based on 70% RES. VI is computed with different variables that may be related to climate change, the energy matrix, and vulnerability. Principal Component Analysis (PCA) was used to select the variables involved in the VI calculation. The VI was calculated for the whole country and the 32 departments (states) showing that the regions with the larger vulnerability correspond to the more energy demanding regions. These vulnerable regions to climate change are more than 50% of the maximum possible vulnerability, meanwhile, the vulnerability of the whole country was estimated as 43%. The analysis was developed for the current situation of Colombia in which there are two regions: interconnected (SIN) and not-interconnected (ZNI) areas.