Cyclic environmental events, such as the El Niño Southern Oscillation (ENSO / El Niño) phenomenon may add to the development or worsening of mental disorders and may have a negative psychosocial impact. Little is known of the effects of El Niño on the mental health of residents from historically vulnerable zones, such as the northern coast of Peru. Community-based strategies, such as those based in theories of Social Capital (SC), may increase mutual cooperation and lower the risk for mental disorders, increasing post-disaster resilience. Using a mixed-methods approach this thesis aimed to understand the effects of El Niño-related events on mental health of affected residents of Tumbes, Peru, explore their perceptions on their mental well-being and identify resilience strategies that would help them to overcome future El Niño events. First, through a systematic review I identified quasi- experimental studies, randomised controlled trials and pilot studies that evaluated interventions with SC components to improve mental health outcomes. Second, I explored whether time trends of mild depression rates changed by exposure to the El Niño 2015-2016 event, through a secondary data analysis. After adjusting for an a priori set of confounders I linked individual and ecological-level data, from participants of a three-year pragmatic stepped-wedge cluster randomized-trial conducted in Tumbes. Finally, through qualitative research methods, I explored the perceived effect of the occurrence of the El Niño events of 2015-2016 and 2017 on residents’ mental well-being, the individual and community responses, availability and access to support systems and community resilience strategies. I found that communities with chronic exposure to El Niño events may not have a high prevalence of a mental disorder, such as depression, but they are affected from prior trauma, through relived personal disturbing experiences, relentless distress associated to scarcity, hopelessness related to authorities’ neglect and lack of community resilience. I recommend that policy should include a two-level (individual and community) approach, with greater emphasis on psychosocial and community empowerment support, nested within and alongside structural interventions that improve survivors’ social and material reconstruction of their livelihoods and fragmented social bonds.