Hot, humid days and nights contribute to heat stress, heat-related deaths, reduced labor productivity and can exacerbate poverty. While everyone can be negatively impacted by extreme heat, certain people such as workers, especially those working outdoors in the sun or engaging in physical labor, the elderly and those with chronic illnesses, children and pregnant women are particularly at risk of suffering harm during such hot spells. Climate change is causing temperatures to increase around the globe, and leading to an increase in the number of hot days and nights.
Da Nang is a tropical city in which the humidity rarely drops below 60%; the humidity is always
high. Humidity and lack of wind can make a day or night feel even hotter than what the thermometer
registers, and as the body experiences increasing difficulty in cooling itself through sweating.
Heat stress indices have been developed to describe how hot it actually feels to people based on
humidity, temperature and physical activity, among other factors. We developed a heat stress index
for Da Nang to measure how the number of hot days and nights has changed in the past (1970-‐2011)
and how climate change might increase these in the near future (2020-‐2049).
The Vietnam Ministry of Health (MOH) regulations specify that temperatures in a work environment
should not exceed 34°C for light work (desk-‐based jobs) or 30°C for heavy work (construction,
outdoor labor, etc.) when the humidity is 80% or lower. At humidity higher than 80%, the
temperature thresholds are even lower because dangerous heat stress conditions can rapidly develop
and endanger workers’ health. Over the period of 1970-‐2011, there were an average 210
(295) days per year in which the heat index was equal to or greater than the MOH’s
recommendations of 34°C (30°C) for light (heavy) labor. On average, the number of days per year in
which the heat index exceeds 34°C has increased by approximately 5 days per decade.
Multi-‐model projections of future day and night ambient temperatures and heat index values under
nearly all climate change scenarios show continued warming through 2050. Warming is most pronounced in the months leading up to (April and May) and just after (September through November) the hot season, though the hot season will also get warmer. Because of these increases in ambient
temperature, the heat index during the day begins to continually average above 40°C during May
through September, creating dangerous working conditions for both outdoor and indoor workers. The
median heat index during the day is not likely to fall below 35.1°C during any season by 2050,
putting both outdoor and indoor workers at risk of heat stress unless a variety of coping
mechanisms are adopted. Nighttime temperatures and heat indices are also likely to increase, not
allowing individuals to recover while they sleep. When factoring urban heat island effects, future heat stress in Da Nang could be significant.
The rapid construction of buildings and roads, additional cars and air conditioning in Da Nang are
trapping heat in the city – this is known as the urban heat island effect and can make temperatures
in the urban core up to 10°C warmer than the surrounding rural areas. The potential for urban heat
effects on future heat indices is profound. Outdoor workers in urban areas will be at significant
risk of heat stroke and, possibly, death in the hot season if their localized heat index approaches
45 to 55°C and their employers do not allow them to rest and take protective measures.