The lack of information on how climatic variability affects water resources frequently limits efforts to sustain them. The research objective is to evaluate the water resources vulnerability to climate variability in the Opak Watershed, Special Region of Yogyakarta, Indonesia. The vulnerability assessment focused on how people’s access to water is being impacted by climate unpredictability. The IPCC concept, which states that vulnerability is a function of exposure, sensitivity, and adaptive capacity, was applied in vulnerability assessments. Previous research provided the exposure criteria and indicators (changes in watersheds), sensitivity criteria and indicators (water demand, community dependence on land), and adaptive capacity criteria and indicators (quality of human resources, socioeconomic status, and water catchment area). The vulnerability map was then created by assigning criteria and indications a score and weight based on how important they were, geographically displaying them, and superimposing them with the use of mapping software. Results showed that according to the vulnerability map, 49% as having a slightly low level of vulnerability, 24% as having a low level of vulnerability, 21% as having a moderate level of vulnerability and 6% as having a slightly high level of vulnerability. Based on the watershed region, the sequence of vulnerability levels from moderate to lowest is the middle, downstream and upstream regions. These findings may help the Local Government or the Opak Watershed Authority develop plans, strategies, and other efforts to deal with the issue of how climate variability is affecting water resources.