Hong Kong has been at the mercy of spells of torrential rain and thunderstorms for the past week. Up until 22 June, the total amount of rainfall since the beginning of June has reached 622mm – much higher than 456mm, the monthly average of June over the last 30 years.

Downpours are the norm from May to August for a tropical region like Hong Kong. Besides the floods and traffic congestion that lead to collective groans from the public, is there any substantial evidence that connects bad weather and bad mood?

Weather lovers or haters: Which one do you belong to?

Bad weather is generally considered as one of the reasons leading to bad mood. On the contrary, more sunlight, warmer temperatures and higher barometric pressures have been associated with better moods (clear, sunny weather is associated with high pressure).

In 1984, psychiatrist Dr Norman E. Rosenthal introduced the term seasonal affective disorder (SAD) to illustrate the weather-mood relationship. He described the term as a psychiatric “syndrome characterised by recurrent depressions that occur annually at the same time each year”.

SAD may affect a person up to 40% of the year, and is commonly experienced during autumn and winter (Winter SAD). That being said, there are patients who are diagnosed with SAD during the spring and summer months (Spring SAD), as well. Patients with Winter-onset SAD tend to develop atypical depressive symptoms – displaying an increased inclination for sleep and an increased appetite. Meanwhile, patients with Spring SAD tend to develop typical depressive symptoms, such as insomnia and loss of appetite.

However, not everyone’s mood is affected by weather. A novel study conducted in Belgium tried to investigate the effect of mood on weather by categorising 497 adolescents into four unique groups, namely:

1. Summer Lovers (improved mood with sunnier and warmer weather);
2. Summer Haters (the inverse of Summer Lovers);
3. Rain Haters (worse mood on rainy days); and
4. Unaffected (people who do not have their moods significantly linked to weather).

Results have showed that approximately half of the surveyed population fell into the ‘Unaffected’ subgroup. Interestingly, mother-child pairs tend to display the same ‘weather type’.

Weather may also influence cognitive functions

Apart from mood, weather may influence cognitive functions. In a study carried out by researchers from the University of Virginia and University of Houston, two groups of participants need to proofread an article at temperatures of 25°C and 19.4°C, respectively.

Results revealed that participants in the warmer setting did significantly worse than the other group in the cooler room – missing nearly half of the errors in the article. Subsequently, researchers tried to replicate the findings in even more complex decision-making tasks, such as choosing between two cell phone plans. The findings suggested that even a mild fluctuation in temperature could contribute to tangible changes on cognition functions.

Researchers explained that human body spends valuable energy adjusting to a more comfortable temperature under a warmer environment. Hence, this requires depleting the glucose supply needed for mental processes. Nevertheless, these findings do not necessarily mean that people from cooler climates are ‘better’ – cognitive changes only become apparent when the temperature fluctuates from the expected norm. MIMS

Read more:
The rise of non-communicable diseases in Hong Kong amid climate change
Hot weather can increase risk of dehydration and heat stroke in persons
From electrotherapy to wearable brain stimulation devices – Treating depression and elevating mood
Mental health in Hong Kong: failing system and its consequences