Extreme heat events are becoming more common as the climate warms. Cities around the world, but particularly in the Global South, are scrambling to cope, their buildings and infrastructure not designed to counter such dangerous temperature levels. This heat leads to humidity. And humidity — the amount of water vapor in the air, or that muggy feeling — can lead to fatigue, fainting or worse.
“If you’re sitting in the shade with unlimited drinking water in California’s Death Valley, conditions may not be pleasant, but they’re survivable,” says Colin Raymond, a climate scientist at NASA’s Jet Propulsion Laboratory in Southern California. “But in humid regions, once you approach wet-bulb temperatures of 34-to-36 degrees Celsius (93-to-97 degrees Fahrenheit), it doesn’t matter what you’re doing. You can’t survive for extended periods of time.”
Heat and humidity can feel particularly intense in the city. And the World Economic Forum predicts that the percentage of the world population living in cities will rise from 55% now to 80% by 2050. With more dramatic steps needed by both urban institutions and city-dwellers, HouseFresh has identified the most humid cities in the world and ranked every major city by the number of days per year that each major city is humid.
Key findings
- Honolulu (Hawaii) is the most humid major U.S. city, with 337.1 uncomfortably humid days per year.
- Singapore, Macapa (Brazil) and Cartagena (Colombia) are among the most humid global cities, with 365 uncomfortably humid days per year.
- Portsmouth is the most humid UK city, with 11.7 uncomfortably humid days each year.
- Hamilton is Canada’s most humid city, with 52.7 uncomfortably humid days per year.
- Cairns is Australia’s most humid city, with 315 uncomfortably humid days each year.
What we did
We analyzed Weather Spark’s humidity data for 14,657 major cities to find how many days in 2023 each experienced a dew point of at least 16°C (60°F). We ranked cities with the most days above this level as the most humid.
Dew point is the temperature at which perspiration evaporates from the skin, cooling the body, so higher dew points feel more humid. This makes it a more accurate measure of how muggy it feels on a given day compared to relative humidity.
Before we dive into the results of our study, have a read at the mini-infographic below to learn more about the difference between relative humidity and dew point:
The most humid cities in America
We found that Honolulu in Hawaii is the most humid major U.S. city, with 337.1 days per year when the dew point is 16°C (60°F) or over. However, Florida is the state with the most major cities among America’s most humid. There are seven Florida cities in the top ten, each with over 208 days per year of high humidity.
Honolulu is significantly more humid than any major U.S. city outside of Hawaii. The island state is more than 2,000 miles from the main continent and is surrounded by sea with a surface temperature that rarely dips below 22 degrees, causing moisture to rise from the ocean and contributing to humidity.
However, the humidity is far from uniform in Hawaii. The dramatic lay of the land plays a major part in modulating weather effects, and winds rushing down from the mountains can dry the air, worsening another climate-related threat: wildfires, such as those that engulfed Maui last summer.
Our study shows that the most humid Hawaiian cities eclipse mainland humidity levels. For the map below, we expanded from major cities to include all U.S. cities with a population of more than 10,000 people. We found that Kailua, to the north-east of Honolulu on the island of Oʻahu, is the most humid city of this scale in America, suffering from 342.9 humid days per year.
The second most humid city with a population of over 10,000 is Homestead, joining its larger Florida neighbors Miami, Orlando and Sarasota among America’s muggiest places. Homestead suffers from 301.5 humid days per year. Local farmworker Efraín López García died at work in Homestead on July 6, 2023 — the hottest day on record — having suffered “symptoms consistent with heat illness,” according to NBC News.
“All of this could have been prevented with the right legislation,” said Yvette Cruz, Farmworker Association of Florida spokesperson. “All we ask is for four basic things: water, shade, breaks and to work with somebody — not to be left alone.”
The most humid cities around the world
Next, we widened the net to identify the most humid major cities worldwide.
There are seven countries worldwide with cities that have constantly high humidity (365 days per year). Four of these are in Asia, and two are in South America, with Libreville in Gabon, Africa, the seventh.
No North American countries are among the global top 20. But San Pedro Sula in Honduras suffers uncomfortably high humidity 363.5 days a year, so it is not far behind. The city is hot throughout the year but may be a little less humid in April when it tends to rain less.
There are two Mexican cities among North America’s most humid. Cancun suffers from 348.3 uncomfortably humid days per year. The tropical climate and location on the Caribbean Sea combine to create a warm, damp atmosphere, particularly between June and October when it is rainier. To the west of the continent, Acapulco suffers even worse humidity, with Pacific Coastal conditions exacerbated by harsh trade winds.
Next, we looked at Europe, where the humidity level among the most humid major cities is lower than on any other continent. Nine out of the top ten cities are in Spain or Italy, where the climate and moisture from the Mediterranean combine to keep things muggy through the summer months.
The south of Europe also feels the knock-on effects of African weather events. “The bubble of hot air that has inflated over Southern Europe has turned Italy and surrounding countries into a giant pizza oven,” explained Hannah Cloke, a University of Reading climate scientist, during the European heatwave last summer. “The hot air, which pushed in from Africa, is now staying put with settled high-pressure conditions meaning that heat in warm sea, land and air continues to build.”
Conversely, Asian cities (below) are the most humid of all. In fact, the entire top ten suffers from humidity 365 days per year. In order to rank them, we calculated the number of days each city spent at an extreme level of humidity (24°C/75°F dew point or more). By this metric, Balikpapan in Indonesia is the most humid, suffering 365.0 humid days and 268.8 extremely humid days per year.
Asia is particularly susceptible to humidity due to its geographical layout, with vast mountainous regions, proximity to warm seas and intense monsoon seasons creating a “hothouse atmosphere.” Four of the most humid major Asian cities are in the Philippines. Humidity levels reached as high as 97% in May 2023. A 2019 report from the Institute for Economics and Peace suggested that the Philippines is the country most at risk from the climate crisis.
All of South America’s ten most humid major cities are in Colombia or Brazil, and all suffer 365 humid days per year. (As described above, we separated them based on how many days each city spent at an extreme level of humidity of 24°C/75°F dew point or more.)
Cartagena in Colombia is South America’s most humid major city, with 365 days of humidity, of which 248.91 are extreme. The city has plans to construct six embankments and four breakwaters to defend against the onslaught of climate change. Researchers at the Niels Bohr Institute predict that the median sea level will rise by one meter over the next 100 years, which will affect 93% of Cartagena’s tourism zone, according to the Center for Caribbean Oceanographic Research.
The bulk of Oceania’s most humid major cities are in Australia, partly because this is where the majority of the region’s major cities are. However, the Fijian capital, Suva, stands out as the most humid by far, with 356.6 uncomfortably humid days per year.
Fiji’s position puts it on the front line of climate change. “[M]any children in the region have already experienced firsthand the impacts of severe cyclonic events which are happening with greater frequency,” says Milika Sobey, Pacific Islands program manager at The Asia Foundation. “They are experiencing firsthand the warmer ocean, the sea level rise, the destructive storm surges, the eroding coastlines and the trauma of relocation.”
The most humid major African cities barely get a day without uncomfortable humidity each year; all among the top 20 most humid have more than 361 days per year of humidity. Cities from eight different countries are among the top ten, with diverse conditions contributing to local humidity, including proximity to the sea or dense forest cover and a tropical climate induced by closeness to the equator.
Libreville, the capital of Gabon, is the only city where the dew point is always at least 16°C. Gabon is mainly covered by forests and is considered “probably the most carbon-positive country in the world due to its strong environmental conservation and longstanding political commitment to preserving the country’s untouched natural environment.” However, weather patterns are already changing drastically in Gabon, and an increase in heat waves and coastal flooding is likely to impact the country’s biodiversity and the health of locals in cities and rural areas.
In addition to feeling muggy and uncomfortable, high humidity levels can have several effects on human health. This is particularly the case for older people, those with pre-existing conditions and those who are on medication — although young, healthy people are also vulnerable to severe, ongoing humidity.
The effects of dangerous levels of humidity include:
To learn more, check out our guide on how uncomfortable you’ll feel at different levels of humidity.
How to stay safe in high humidity
Once you know humidity is a threat, there are steps you can take to protect your family’s health from the various risks.
- Check the weather before you go: If the weather report suggests high humidity levels, plan to take it easy and not venture too far from well-air-conditioned areas.
- Dress to stay cool: Wear loose clothes to stay comfortable and a hat to keep the sun off your head and face. Light, breathable fabrics in pale, reflective colors will help your body stay cool.
- Drink plenty of fluids: “Drinking enough fluids is one of the most important things you can do to prevent heat illness,” according to the Centers for Disease Control and Prevention (CDC). The CDC recommends drinking water before, during and after activity.
- Be aware of the symptoms: Sweating, cramps, dizziness, an itchy rash, nausea and headaches can all be symptoms of heat or humidity-induced sickness.
Danny Ashton
Founder of HouseFresh
1. Use a dehumidifier. Dehumidifiers pull moisture out of the air and collect it in a tank. Choose an energy-efficient one, and you’ll find it uses far less energy than many other household appliances.
2. Use electric fans. An electric fan creates a breeze to keep you cool but also prevents moisture from settling and improves evaporation levels.
3. Open doors and windows. The simplest solution to keep air flowing through your home and let moisture escape is to give it somewhere to go. If keeping external doors and windows open isn’t possible, keeping interior ones open can still help.
4. Take shorter showers and dry laundry outdoors. Consider ways that your daily routine may contribute to humidity in the home, and take steps to reduce the amount of warm moisture that you create indoors.
5. Get dehumidifying houseplants. Plants such as Baby Rubberplant, Golden Pothos and Aloe Vera are excellent at removing moisture from the air in a room.
For more tips, check out our extensive guide with advice to help you naturally dehumidify a room without a dehumidifier.”
Final thoughts
Sadly, humidity is an issue that is going to get worse in cities all around the world, particularly in parts of South Asia and the Persian Gulf and states including Arkansas, Missouri and Iowa.
While the sick, the elderly and those who work most outdoors are among the most vulnerable to humidity, those “without access to air conditioning” are also vulnerable, according to NASA. “Air conditioning removes humidity from the air and is the best solution when wet-bulb temperatures get too high. Fans can help sweat evaporate more efficiently, but they’re less effective.”
To begin looking for the right dehumidifier for your home, you can start with one of our many guides on which to choose.
METHODOLOGY
To identify the cities worldwide with the most humid days annually, we pulled humidity comfort data from 14,657 major cities from https://weatherspark.com/.
The dew point defines humidity comfort levels. Dew point temperature determines when perspiration evaporates from the skin, cooling the body. Lower dew point temperatures feel drier, and higher dew points feel more humid.
Dew point better represents how humid a city feels than relative humidity. This is explained here and here.
Our study ranks cities based on the number of days each in 2023 with a dew point of 16°C (60°F) or above (the dew point at which the air stops feeling comfortable and starts feeling humid).
For cities that were tied on 365 annual humid days in the South America and Asia rankings, we separated them based on the number of days spent at an extreme level of humidity (24°C/75°F dew point or above).
For the U.S. map, we lowered the threshold to 10k population cities to dive deeper into the most humid cities by state beyond just the largest settlements.
