Environmental changes serve as important risk factors for health. Mental disorders are associated with different aspects of environmental conditions, such as average outdoor temperature, air quality, temperature variation, and seasonal amount of daily sunlight (1–3). These conditions can either directly induce psychosocial stress within individuals or generate confounding effects on physical inactivity, lifestyle, hormonal changes, and social interactions, which then result in changes in mental states (4, 5). Previous studies show that daily extreme weather conditions accompany increased risk for psychiatric disorders (6). It is also found that air pollution and temperature variability lead to declined mental health conditions (7–9). It is unclear how seasonal mild temperature variation is associated with the occurrence or recurrence of mental diseases.

Recent studies employing time-series analyses highlight the potential predictive effects of ambient temperature on mental health conditions (1). For instance, extreme temperatures increase the hospital admission of patients with mental disorders (1, 10), schizophrenia (11) and emergency mental disorders (12). However, few studies have systemically examined the association between temperature and psychiatric hospital outpatient visits over a prolonged period.

In practical management of clinical psychiatric services, it is important to predict the number of outpatients in the coming season. Located in Shanghai, China, a city without extreme weather conditions, the Shanghai Mental Health Center is one of the largest psychiatric clinical service centers in the world with nearly 1 million outpatient visits annually. We, here, retrospectively analyze the dynamics of outpatients visiting the center from January 2014 to March 2019 together with the temperature changes during this period. The results suggest an effect of environmental–cultural interaction on psychiatric outpatients.

The study demonstrates that temperature factors impact the number of clinical psychiatric outpatients significantly. Higher temperatures can be associated with increased psychiatric conditions as evidenced by the increased number of outpatient visits to public clinics. This makes it possible for public health administration departments to forecast the volume of psychiatric outpatients by taking monthly or even weekly and daily temperature dynamics into consideration.

The concurrent monthly temperature had a stronger effect on first-time rather than recurring patients in all subdivisions (marginally significant for children's psychiatry), suggesting that the current temperature did impact the mood status of already diagnosed patients, but it might act as an important cause for a patient's first episode of mental disruption. Notably, 1-month lagged temperatures were correlated to number of first-time outpatients in psycho-consultation and children's psychiatry, but not in general psychiatry. It is possible that the general psychiatry patients were more sensitive to high temperatures, and they sought treatment at clinics immediately after the temperature change while the psycho-consultation patients had mild conditions and the children were taken to the clinic by their parents, both of which resulted in prolonged treatment-seeking timelines.

It is also notable that the number of recurring outpatients did not show significant correlation to temperature conditions. It is highly possible that these patients were compliance with treatment and some knowledge of their own diseases, and therefore, they could partly self-adjust to environmental changes. However, it is important to divide these patients into different subcategories, such as bipolar disorder, schizophrenia, and major depression, in order to perform detailed analyses for each psychiatric condition.

Notably, for the years included in the analyses, seasonal dynamics were similar across different years although with a yearly increasing trend. February happened to have the fewest outpatients in a year. This is potentially due to the Chinese New Year festival; as a cultural period for family union, patients may have tended to take vacations to travel back home. This suggests that social factors interact with environment changes in prediction of outpatient visits.

In conclusion, the present study reports that environmental temperature correlates to the number of psychiatric outpatients. This offers some insight for hospital management into improving outpatient service qualities.

The datasets generated for this study are available on request to the corresponding author.

Ethical review and approval was not required for the study on human participants in accordance with the local legislation and institutional requirements. Written informed consent was not required to participate in this study in accordance with the national legislation and the institutional requirements.

YaS and J-MF designed the study. YiS, JX, YQ, YaS, and J-MF performed the study, analyzed the results, and wrote the paper together. All authors have read and approved the final version of the manuscript.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.