Subtropical and tropical zones and their influence on the indoor climate

In the first part of our blog series on climate conditions worldwide, we looked at the different climate classifications and the influence of the temperate zone on the indoor climate. In this second part, we present the subtropical and tropical zones. We take a more in-depth look at some of the Asiatic regions based on their classification according to the Köppen-Geiger system.

Read on to find out about: 

1. The tropical zone: year-round high temperatures and a diurnal climate
2. Characteristics of the dry, humid winter and constantly humid subtropics
3. The climate in China: climate diversity and East Asian summer monsoon 
4. The main phenomena of the East Asian summer monsoon in China
   
5. Tips and tricks for coping with the high level of humidity in China
6. The climate in Malaysia: a tropical climate
7. The climate in Malaysia and the influence on well-being and indoor climate
8. The climate in Hong Kong: subtropical and humid
9. The influence of the climate in Hong Kong on life and living
10. The subtropical and tropical zones and their influence on the indoor climate

The tropical zone: year-round high temperatures and a diurnal climate

The tropical zone is characterised by its proximity to the equator which leads to characteristic climate conditions. It encompasses many countries in South America, Central America, Africa, Asia and Oceania. Temperatures in the tropics fluctuate more during the course of a day than they do throughout the year. That is why the climate here is also described as diurnal. The tropics do not have distinct seasons. Generally, there are few seasonal variations here and the average temperatures lie between 25 and 35 degrees Celsius all year round. Because of their proximity to the equator, the tropics get more sunlight than other regions which contributes to the warm temperatures.
Another distinctive characteristic of the tropics is the high level of humidity. Due to the high temperatures, a lot of water evaporates and this moisture is absorbed into the air. This leads to muggy conditions that many people from non-tropical regions can find unfamiliar and sometimes unpleasant. The high level of humidity can also affect the perceived temperature and lead to an increased perception of heat.

The tropics are also known for their frequent rainfall. The combination of high temperatures and high humidity leads to the formation of clouds and eventually to rain. The Köppen-Geiger classification indicates a minimum average rainfall of 60 millimetres during the rainy season. In many tropical areas, there are two main rainy seasons, characterised by heavy rainfall. This regular rainfall promotes the growth of lush rainforests which are known for their biodiversity.

Characteristics of the dry, humid winter and constantly humid subtropics

The subtropical zone extends between the temperate latitudes and the tropics. It encompasses many countries and territories worldwide – for instance, the whole of the Mediterranean region is classified as subtropical. The climate conditions in the subtropics are shaped by characteristic features that can vary depending on the geographical location. A distinction is generally made between dry, humid winter and constantly humid subtropics.

The dry subtropics are known for their hot and dry summers as well as mild winters. These regions are located close to the equator and are characterised by desert and steppe vegetation. The Atacama desert and the Sahara are classified as being in the dry subtropics, for example. The prevailing climate here is seasonal, with temperatures fluctuating more within a year than they do within a day. On average, the temperature in the dry subtropics is above 20 degrees Celsius.

The further you move away from the equator towards the poles, the more humid it becomes. The climate in the humid winter subtropics is characterised by warm and dry summers and mild winters with moderate to high rainfall. Temperatures remain mild in winter too, with an average of 10 to 15 degrees Celsius. The Mediterranean region, Southwest Australia and South Africa are all part of the humid winter subtropics.

The constantly humid subtropics are characterised by high temperatures and high rainfall all year round. They are located near the coast, where warm ocean currents and trade winds mean constant humidity. Rainfall is particularly heavy in summer. At this time of year, the monsoon winds from the east bring a lot of moisture that they pick up from the sea. The regions with constantly humid subtropical conditions include, for example, the east coast of the US, Eastern Australia and East Asia.

Now you are familiar with tropical and subtropical climate conditions, we are going to focus on China, Malaysia and Hong Kong.

The climate in China: climate diversity and East Asian summer monsoon

Attribution: Beck, H.E., Zimmermann, N. E., McVicar, T. R., Vergopolan, N., Berg, A., & Wood, E. F., CC BY 4.0, via Wikimedia Commons

In China, there is great climate diversity. According to the Köppen-Geiger classification, all the types of climate can be found here. The eastern side of the country has a wide range of monsoon climates. The winter here is characterised by a continental monsoon climate which is cool and dry. In summer, the climate is characterised by the East Asian summer monsoon which brings a humid, hot and rainy climate. With its altitude and expanse, the Qinghai-Tibet Plateau in south-western China has a unique alpine climate. And the north-western region has the oceanic monsoon and is characterised by a westerly, dry continental climate.

As the humid conditions of the East Asian summer monsoon have a significant effect on people’s well-being and the indoor climate, this is the climate phenomenon I would like to focus on below.

The main phenomena of the East Asian summer monsoon in China

• South China’s flooding season: The earliest onset of the flooding season is usually in March or April. The summer monsoon starts in May with the onset of the monsoon over the South China Sea which initiates the peak period of the rainy season. The summer monsoon outlasts the midsummer period, bringing frequent flood events such as flooding, before coming to an end at the end of July.
• Jianghuai Meiyu period: The so-called Meiyu front is a characteristic of the summer monsoon. In mid-June, when the summer monsoon pushes northwards and the subtropical high jumps northwards, the main rain belt reaches the middle and lower reaches of the Yangtze. This period is known as the Jianghuai Meiyu period in China. In some years, the rain goes on for longer. In 2020, for example, the rainy season reached the Yangtze basin as early as May. Today, the Meiyu area extends to the whole Jiangnan, Jianghan und Jianghuai region. The main rainy season in the middle and lower reaches of the Yangtze generally lasts until the beginning of July.
• The northern main rainy season: After mid-July, the warm humid period of the year reaches its peak, when the prevailing wind direction and the subtropical high move north. That is when the country experiences the most humid time of the year. At this time of year, typhoons and easterly precipitation can sometimes occur on the southern side of the subtropical high, which in turn can lead to a post-flooding period.

With the arrival of the main rain belt during the rainy season, the prevailing climate brings high temperatures and high humidity which can get up to 80 to 100%. In China, problems experienced in the humid areas include clothes not drying properly, spices clumping together, floors swelling, walls peeling and mildew forming on books as well as musical instruments as a result of which their sound changes. Because of that, China has developed its own methods for reducing humidity. Here are a few examples.

Tips and tricks for coping with the high level of humidity in parts of China

• Doors and windows: During the rainy season, the Chinese keep their doors and windows closed to keep the humidity out.
• Vacuum cleaner bags and dehumidifiers: One method for protecting clothes against moisture is to place vacuum cleaner bags and dehumidifiers in wardrobes.
• Hairdryers and tumble dryers: Hair dryers are not only used to dry hair but also to dry damp clothing. Tumble dryers are also used as an alternative.
• Screens, desiccants, etc.: Moisture-proof screens, desiccants and suchlike are used to protect household items against moisture.
• Using a dehumidifier: Especially when the air is extremely humid, using a dehumidifier is an efficient way of reducing the level of humidity indoors quickly.

The climate in Malaysia: a tropical climate

In Malaysia, there is a tropical rainforest climate (Af) and a monsoon climate (Am) according to the Köppen-Geiger classification. Malaysia’s position on the equator means that the climate is hot and humid all year round. The climate conditions vary within the country, with the climate on the Malaysian Peninsula being different to the climate in the east where the maritime weather has more of an influence. The average temperatures in Malaysia range between 28 °C and 32 °C, however in the months of March and April it can get up to 38 °C. On the eastern coast of the Malaysian Peninsula, a monsoon climate characterised by heavy rainfall prevails from November to March.

Like some regions in China, Malaysia also has a very high level of humidity which varies between 98% in the morning and around 70% in the afternoon. These climate conditions can also affect people's well-being and the indoor climate.

The climate in Malaysia and the influence on well-being and indoor climate

The heat and high level of humidity can be physically draining and lead to exhaustion. The climate can influence perception, reduce productivity and affect physical health. It is therefore important to dress accordingly, drink plenty of water and protect yourself from the intense rays of the sun. Many people wear light, loose-fitting clothing and use shade-giving parasols or headgear, for example, to protect them from the sun’s rays. In some households, fans are also used.

With regard to the indoor climate, the high level of humidity – which also develops in interior spaces – plays a significant role. Mould, spores and fungi are ever-present, especially in leather materials. A lot of people use moisture absorbers which they put in wardrobes and drawers to reduce moisture problems. However when it comes to preventing mould from forming indoors, dehumidifiers are once again the best option. They can permanently reduce the level of moisture and are an efficient solution.

The climate in Hong Kong: subtropical and humid

Hong Kong lies in the subtropics and has a humid subtropical climate (Cwa). Hong Kong has four seasons: spring is relatively mild but quite humid and foggy; summer is hot to very hot and rainy; autumn is warm, dry and sunny and winter is cool and dry.

The various months of the year have different characteristics. In January and February, there are clouds and occasional cold fronts that bring dry northerly winds. In urban areas, the temperature sometimes drops below 10 °C. In March and April, it is warmer but occasionally extremely humid. Fog and drizzle reduce visibility and sometimes affect air and ferry traffic. From May to August, it is hot and humid with occasional showers and thunderstorms. In the afternoon, temperatures often rise above 31 °C and remain at around 26 °C at night.

July, August and September are the months most likely to be affected by tropical cyclones. In November and December, there are sunny days with moderate temperatures and a pleasant climate.

The influence of the climate in Hong Kong on life and living

In Hong Kong, air-conditioning systems, fans and dehumidifiers are used to create a pleasant indoor climate. Every household should own a dehumidifier as a minimum and dehumidify the house thoroughly at least once a week, especially in the spring or on rainy days.

Tropical cyclones also have an influence on life and living in Hong Kong. Because of its geographical location, Hong Kong is prone to tropical cyclones, also known as typhoons. Typhoons are strong tropical cyclones which normally occur between June and November, with most activities happening between July and September. Hong Kong is located in a region where typhoons can occur as it is surrounded by waters such as the South China Sea and the Western Pacific where these storms arise.

The impact of typhoons can have severe consequences for people and the environment. Because of that, the Hong Kong government has developed a well-organised system for monitoring and predicting typhoons. The Hong Kong Observatory is responsible for issuing warnings and providing information on the development of typhoons. In addition, structural measures to minimise the impact of typhoons have been taken in Hong Kong. Buildings are constructed in accordance with strict regulations and standards to enable them to withstand stronger winds.

Subtropical and tropical zones and their influence on the indoor climate

Subtropical and tropical zones are characterised by their high temperatures and high level of humidity. As a result of this combination, the air in indoor spaces is often sticky which can affect general well-being. The high level of humidity can also lead to humidity-related problems indoors such as e.g. the formation of mould or clothing being constantly damp. To counteract these problems, various countries have developed different methods such as placing moisture traps in cupboards, for example. In any case, the use of a dehumidifier is recommended in order to keep the level of humidity within an ideal range of between 40% and 60%. On particularly hot days, fans can provide relief and a cool breeze. In buildings where air-conditioning systems are used for cooling, it is important to keep an eye on the level of humidity. If such systems are set to a temperature that is too cold, it will make the indoor air dry. If the indoor air goes below 40%, a humidifier should also be used.

In the next part of this series we will be looking at the climate in the Mediterranean and presenting to you the climatic conditions in areas such as the Lebanon and the coastal region of Slovenia.

* This article was written with the collaboration of the following Stadler Form distributors:

• China: Zhejiang Baiyang Electric Appliance Co. Ltd
• Malaysia: Blue Orange Resources SDN BHD
• Hongkong S.A.R., China: Union Camera Hong Kong Ltd.

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