Both relative humidity and dew point are widely used indicators of the amount of moisture in the air.
Relative Humidity: The ratio of how much moisture the air is holding to how much moisture it could hold at a given temperature and indicated by a percentage.
Dew Point Temperature: The highest possible temperature that water vapor can condense to form water droplets known as dew.
So what’s the difference between dew point and relative humidity?
The main difference is that relative humidity is dependent on temperature and is relative to that specific temp. The dew point is the temperature at which the air can no longer "hold" all of the water vapor, so some of the water vapor condenses into liquid water, usually in the form as fog, precipitation or dew.
Dew point: An accurate measurement of "humidity"
Relatively humidity is often misleading because warmer air can hold more moisture than cold air. For every 11°F increase in temperature, air’s ability to hold water doubles. For example, at 37°F with 100% relative humidity, the same exact amount of moisture in the air would equate to 20% relative humidity at 86°F. As for a dew point example:
40°F outside with a dew point temperature of 40°F = 100% relative humidity
75°F outside with a dew point temperature of 60°F = 60% relative humidity
Because dew point is a more reliable indicator of humidity, this articles uses it to answer three questions about humid places around the world:
What is the most humid city in the world?
What is the most humid country on Earth?
What’s the most humid place?
(Image Source: Cizauskas)
1) Most Humid City in the World
Pearl-Qatar - an artificial island in Qatar
There are several contenders for the most humid city in the world, based on which city across the globe has the highest dewpoint, and records incredibly high dewpoints all year round. Cities located almost directly on the Equator, have a constant wet season and intense heat, and are close to a large stretch of warm water are most likely contenders.
These include many cities in tropical Equatorial climates, such as:
Kuala Lumpur
Singapore
Jakarta
Manaus
However, other cities have recorded higher dew points, particularly around the Gulf of Aden and Persian Gulf regions, but only during the summer months.
Kuala Lumpur
Kuala Lumpur and Singapore record incredibly high dewpoints across the entire year. Average maximum dew points in Kuala Lumpur reach an impressive high of 83.3°F (28.5°C) during April, only falling to 80.2°F (26.8°C) during August.
However, Singapore is slightly more humid, with maximum average dewpoints of 83.8°F (28.8°C) recorded in April, and 81.9°F (27.7°C) recorded in August. This is not surprising as Kuala Lumpur and Singapore are located around 340 km (210 miles) and 140 km (90 miles) north of the Equator respectively, with an overhead Sun providing intense heat all year round. Both cities are also located close to a large body of water – Singapore borders the large Singapore Strait, whereas the centre of Kuala Lumpur is located around 40 km (25 miles) to the west of the Melacca Strait. The strong sunlight evaporates water from the warm surrounding seas, which in turn increases the moisture content of the air.
However, Manaus in Brazil also records comparatively high dewpoint values throughout the year. With a latitude of 3°S, and its location on the Amazon River in the middle of the Amazon Rainforest, it is no surprise that the average maximum dewpoint fluctuates between 81.3°F (27.4°C) in July and 83.7°F (28.7°C) in October.
Some cities around the world have seen higher dew point values than those already presented, but only during certain times of the year. Bangkok sees higher average maxima – of 85.3°F (29.6°C) in April and 83.7°F (28.7°C) in September, but dewpoints fall to below 78.8°F (26°C) during December and January.
Other high values are recorded seasonally, particularly around the Red Sea, Gulf of Aden and Persian Gulf regions. Despite being on the edge of a hyper-arid desert region, large evaporation rates and high sea surface temperatures combine to produce incredibly high humidity along the coastal regions between May and October.
Jakarta, the capital of the Republic of Indonesia
The highest dewpoint recorded on Earth is in the city of Dhahran in Saudi Arabia, which experienced a dewpoint of 95°F (35°C) in 2003 – however, dewpoints above 90°F (32°C) are rare, and only occur in these regions during the summer months. For example, the city of Muscat is situated in Oman and overlooks the Persian Gulf.
Average maximum dewpoints above 84°F (29°C) in July and August regularly occur in Muscat, but these fall below 68°F (20°C) during December, January and February. Similar seasonal variations occur across the entire region.
(Hosseinzadeh Talaee et al.)
2) Most Humid Country in the World
Palembang, Indonesia
Identifying the most humid country in the world depends on numerous factors. Many countries have large differences in terrain, elevation, and climate.
Although the highest dewpoints in the world have been recorded on land bordering the Persian Gulf, Gulf of Aden, and the Red Sea, these are only limited to the coastal regions of the countries which border those seas.
For example, Saudi Arabia, Oman, and Yemen record dewpoints in excess of 86°F (30°C) along their coastal regions, but their large desert interiors located far from the surrounding seas record comparatively low dewpoint values.
This piece examines countries that have rather high dewpoints recorded across most of their terrain, and maintain the values during much (if not all) of the year.
The small country of Qatar is a strong contender for being the most humid country in the world. Despite its desert landscape and hyper-arid climate, it is a narrow peninsula located on the western side of the Persian Gulf, meaning that it is surrounded by water on its eastern, northern and western sides. Its maximum width of 90 km (55 miles) across means that much of the country is close to water. Its capital city, Doha, records dewpoints exceeding 81°F (27°C) between July and October peaking at 86°F (30°C) in September. However, there is a wide seasonal difference, with dewpoint values below 68°F (20°C) between December and March, meaning that the incredibly humid summer months are cancelled out by the winter months, which are significantly less humid.
Other contenders are likely to be an island, archipelago or coast-bordering nation that is close to the Equator, and has much of its terrain at or near sea level. Although many Equatorial countries that include large rainforests are rather humid, these often include many large upland areas that are cooler due to the lapse rate, making these countries less humid overall than other nations.
Singapore is both a city and a small country in its own right – since its average maximum dewpoint fluctuates between 81 - 84°F (27.7 - 28.895°C) throughout the year, it would be fair to declare this as the world’s most humid country overall.
But what about countries with a larger land mass? Both Malaysia and Indonesia have large lowland areas, despite the presence of large mountain ranges. Indonesia in particular straddles both sides of the Equator, and is made up of a vast archipelago that includes many islands surrounded by warm seas that often top 86°F (30°C). Inland areas of Indonesia also record high humidity levels, such as the city of Palembang around 75 km (45 miles) from the nearest sea. Here, dewpoint levels between 82 - 84°F (28°C and 29°C) are recorded throughout the year – this incredible humidity is felt across much of Indonesia all year round.
3) World’s most humid place
Persian Gulf of Qatar
Although the coastal area alongside the Persian Gulf records incredibly high dewpoints, the coast of Eritrea along the Red Sea has the highest dewpoint in the world. This is due to a combination of incredibly high levels of strong and uninterrupted sunshine, as well as high water temperatures in the southern section of the Red Sea, which often exceed 90°F (32°C) during the hot months. For example, average maximum water temperatures alongside the port town of Assab in Eritrea peak above 86°F (30°C) between June and October. These factors produce incredibly high evaporation rates along the coastline, resulting in incredibly humid air along the Eritrean coast.
The air is moister along the south-western coast of the Red Sea than it is along the Persian Gulf. Like much of Arabia, the Persian Gulf is surrounded by a hyper-arid desert landscape, which limits the levels of humidity in the area to a small degree. However, although the terrain along the south-western side of the Red Sea is also rather dry, it is not as hyper-arid as the Middle East. For example, in Assab, at least one rainfall day is recorded per month. The wettest month is August, which sees an average of 29 millimetres of rain falling in the town, and around 80 millimetres of rainfall across an entire year.
The Blue Nile Falls is a waterfall on the Blue Nile river in Ethiopia. It is known as Tis Abay in Amharic, meaning "great smoke"
The country of Ethiopia lies to the south of Eritrea – it is significantly less arid than the coastal regions around the Persian Gulf. This is in part due to its high altitude, with its large Ethiopian Highlands mountain range promoting a rather temperate climate, but also in part due to its latitude – it is far enough south to receive an annual monsoon season. The Ethiopian Highlands receive enough rain to be rather vegetated. The position of areas with relatively high rainfall rates (and therefore lower aridity) located significantly closer to the Eritrean coast means that the air will be more humid along the Red Sea than it will around the Persian Gulf.
Valentina is a guide for Pedal Chile and is our resident badass. Valentina was born and raised in La Patagonia, which probably explains her affinity for adventuring. When Valentina isn’t crushing some poor dude’s soul, you can find her shredding down Rucapillán. Favorite season: Austral Summer
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Sources & References
Cizauskas, Thomas. “Dew Point.” Flickr, 9 Aug. 2017, www.flickr.com/photos/cizauskas/36373448982.
Hosseinzadeh Talaee, P., et al. “Observed Changes in Relative Humidity and Dew Point Temperature in Coastal Regions of Iran.” Theoretical and Applied Climatology, vol. 110, no. 3, 29 Mar. 2012, pp. 385–393, 10.1007/s00704-012-0630-1.
Raymond, Colin, et al. “The Emergence of Heat and Humidity Too Severe for Human Tolerance.” Science Advances, vol. 6, no. 19, May 2020, p. eaaw1838, 10.1126/sciadv.aaw1838.
US Department of Commerce, NOAA, National Weather Service. “Dew Point vs Humidity.” Weather.gov, 2019.
Weather Atlas. “Āssab, Eritrea - Detailed Climate Information and Monthly Weather Forecast.” Weather Atlas, www.weather-atlas.com/en/eritrea/assab-climate.