Natural disasters, such as floods, cyclones, droughts and fires have become more intense during the last four decades when the planet has warmed by more than 0.5 °C [1
]. With continued emissions, these disasters are predicted to increase as a consequence of climate change [1
]. The annual western forest-fire area in the US increased by ~1000% from 1984 to 2017 [3
]. Since the 1970s to 2018, particularly California has witnessed an eight-fold increase in the areal extent of fires [4
]. During the same period, California (CA) has warmed by 1.4 °C (about 50% greater than global warming estimates) largely due to anthropogenic sources [1
Recent studies [5
] have provided compelling evidence that climate warming has had a definitive role in CA fire extremes. These studies show that year-round warming has increased the aridity of the region due to the exponential increase in evaporation with temperature. The response of the fire extent to aridity is exponential, i.e., warming-driven fuel drying is increasingly impactful. Essentially, climate change is a force-multiplier, accelerating the pre-existing propensity of fires in CA. Between 2017 and 2018 alone, there were approximately 16,000 wildfires reported in this state, with 2 million acres of land burned, resulting in USD 13.7 billion in costs of damages, and ~250 reported injuries, 25% of which resulted in death [7
Weather extremes driven by climate change, such as the California wildfires, are associated with huge costs to human health [9
]. It is projected that the US population exposed to such climate extremes will nearly double by 2050, affecting nearly 25% of all humans in the US each year [12
Prior studies have stressed the mental health consequences of environmental disasters [10
]. Yet, we need to better study the mental health impacts in the context of weather disasters exacerbated by climate change. Such disasters could expose specific vulnerabilities and mental health outcomes that may be unique to climate change-driven events and not to routine natural disasters. The main distinction between naturally occurring weather disasters from those amplified by unchecked anthropogenic climate change is that weather disasters forced by climate change will progressively get worse [12
The two most common adverse mental health outcomes of natural disasters are depression and post-traumatic stress disorder (PTSD) [14
]. While research provides evidence for a cumulative impact of exposure to disasters [17
], most studies report data from the aftermath of a single disaster, and most of those again are classified as natural disasters, unlike recent climate change-driven extreme environmental events. Prior studies of wildfires provide evidence for mental health sequelae, particularly for PTSD symptoms in California residents in the immediate aftermath of the 1991 firestorm [19
]. Symptoms were shown to substantially decrease over time [20
]. PTSD symptoms were also found in firefighters one month after the occurrence of wildfires in Greece [21
]. Yet, to the best of our knowledge, no research to date has addressed distal mental health outcomes, i.e., PTSD, depression and anxiety symptoms in civilians differentially exposed to recent climate change exacerbated wildfires.
A causal pathways framework suggests direct effects of climate change on mental health through exposure to traumatic stressors, as well as indirect effects mediated by impacted physical health, physical environment or community wellbeing [22
]. Prior research suggests that an adverse impact of environmental disasters is dependent on the degree of disaster exposure. In those studies, degree of exposure was defined objectively (e.g., as geographical distance of residence from the epicenter of the disaster) [24
] or subjectively (e.g., as degree of household damage) [24
]. It has also been shown that PTSD symptoms occur in relation to fire exposure particularly in highly exposed individuals who have experienced loss of residency or injuries [19
]. However, it remains an open question whether different degrees of physical and mental exposure differentially impact PTSD, depression and anxiety.
Notably, it has also been argued that the impact of fire exposure on mental health is highly moderated by pre-existing vulnerabilities [26
]. Previous research has shown that past-year stressful life events are associated with an increase in current year risk of mental disorders, particularly in adults with adverse childhood experiences [27
]. Adversity in the form of child abuse and/or neglect is a transdiagnostic factor that increases risk for several mental disorders [28
]. A potential mechanism is stress sensitization, i.e., lower tolerance to stress due to adversities experienced early in life. Yet, prior research in the context of environmental disasters, now transforming into climate change-driven extreme events, has not taken these pre-existing vulnerabilities into account as we do here.
Finally, it is important to identify survivors of serious environmental disasters who have the capacity to mitigate adverse outcomes. Particularly relevant in this context is the notion of resilience, i.e., the ability to recover quickly and adapt well in the face of adversities. Yet, only a few studies to date have investigated dimensions of personal resilience in climate adaptation [20
]. One personal resiliency characteristic that has been suggested as a pathway towards achieving sustainable climate adaptation is mindfulness, i.e., a non-judgmental attentiveness to the present moment [30
]. Additionally, psychological resilience can be conceptualized from a social–ecological angle. Particularly, social support has consistently been highlighted as an indicator of resilience [29
]. Specific lifestyle factors may also be protective in the development of psychopathology. While sleep is known to play a crucial role in various mental disorders, recent research increasingly suggests that the relationship between sleep disturbances and symptom severity is bi-directional [31
]. Altered sleep not only temporally precedes the onset of psychopathology but may also serve as a risk or resilience factor [33
]. Similarly, the role of physical exercise in preventing stress-related psychopathology is supported by its effects on several neurobiological factors linked to individual resilience, including attenuation of stress responses and increased release of endorphins [35
In the current study, we aim to understand the mental health sequelae of a serious climate change exacerbated event, specifically, California’s deadliest wildfire to date, the 2018 Camp Fire. Uniquely, we assess mental health in the context of fire exposure, as well as several factors that may serve to impart vulnerability or resilience. Ultimately, we aim to gain some insight towards identifying and supporting individuals who must rebuild their displaced, post-disaster lives.
The current study investigates mental health outcomes of a significant environmental disaster, the deadliest California wildfire in history, the Camp Fire of 2018, which has been shown to be driven by climate change-induced temperature extremes [5
]. Our analyses include three groups of participants that were identified by proximity as well as help-seeking behavior post-fire. Previous research suggests an association between mental health outcomes after disasters and the degree of exposure as measured in distance to the disaster, degree of household damage or physical injury [19
]. In the context of this wildfire, we confirmed whether our cohort was directly exposed (i.e., to whom the fire happened), indirectly exposed (i.e., who witnessed the fire) or not exposed (i.e., who learned about the fire) as per their self-reported fire exposure. With regard to mental health outcomes, significantly higher symptom scores on mental health outcomes were found in directly exposed individuals, particularly for PTSD and depression. These findings align with previous research showing similar short- and long-term impacts of disaster exposure on mental health [51
PTSD, depression and anxiety disorders can all be conceptualized as stress-related disorders for which environmental stressors and individual (biological and psychological) stress responses are central to pathogenesis. In line with this, not only the experience of wildfires but also childhood trauma (i.e., child abuse and neglect) was consistently found to increase risk of all of these symptoms. This may be particularly relevant in the study samples from Chico, where over 70% of the population are reportedly affected by childhood adversities [53
]. Our findings support the notion that adverse childhood experiences may serve as a vulnerability factor for mental health sequelae in adulthood [28
]. Similarly, lower socio-economic status was also initially identified as a consistent predictor of PTSD, depression and anxiety symptoms, aligned with prior research on climate hazards to human health [10
]. However, this association between mental health and socio-economic status was only significant when childhood adversities as well as other cognitive and lifestyle factors were not accounted for.
We further included measures of resilience and resiliency-imparting lifestyle in our study. Several factors, including personal, social, economic, institutional, infrastructure and community resources, may contribute to resilience and adaptation to environmental disaster, and can be used as indicators thereof. Our study focuses on personal resilience as the ability to bounce back after stressful life events, as well as sleep quality, physical exercise, mindfulness and emotional support, which may all contribute to resilience. As hypothesized, we consistently found self-reported resilience to be inversely associated with PTSD, depression and anxiety symptom severity. Further, higher levels of sleep disturbances were related to higher scores on all clinical symptom scales. These results highlight the relevance of sleep in mental health, although our analyses cannot disentangle whether sleep disturbances were symptomatic of the mental disorders or a risk factor to their development [32
Additionally, mood disorders of depression and anxiety were negatively associated with mindfulness. It has been argued that mindfulness may support a fundamental shift in the way we think about and act on local and global ecological crises [54
], and thus plays a role in developing psychological resilience. Recent evidence shows that mindfulness correlates with responses to severe climate events, recovery and proactive climate adaptation [55
]. Although trait mindfulness is considered to relate to greater psychological adjustment following exposure to trauma in general, we did not find an effect of mindfulness on PTSD symptoms. Similarly, a study in Tsunami disaster survivors did not find a positive effect of trait mindfulness on PTSD symptoms, indicating that mindfulness may not be a protective factor against post-traumatic stress in trauma-exposed individuals [56
]. Much interventional research shows that mindfulness can be enhanced and serve to provide positive mental health benefits, which should be encouraged in these vulnerable communities [57
]. Finally, physical exercise was found to only have a positive effect on depression symptom severity. While we found no positive effect of emotional support on any of the mental health outcomes, future work with a focus on different socio-emotional protective factors may further elucidate the role of family and community in coping with mental health impacts.
A limitation of this study is an inhomogeneity of socio-demographic characteristics between study participants that were recruited at different sites, and thus a lack of representativeness of samples. While samples were selected with respect to the degree of proximity to and affliction by the 2018 Camp Fire, differences in socio-demographic characteristics may have introduced biases. Particularly, family affluence as an indicator of SES may be directly associated with the degree of fire exposure (e.g., by a loss of family belongings due to the fire) and may thus have skewed subjects in the primary proximity and help-seeking sample with high prevalence of direct fire exposure to lower SES. However, with variance inflation factors of <3 for all independent variables, multicollinearity between fire exposure and socio-demographic variables, and thereby confounding effects between those variables can be widely ruled out. Additionally, Cohen’s f2 indicated unique effects, particularly of fire exposure on explained variance in outcome measures.