Why does it rain so much in Belgium?


28 februari 2019
Auteur(s): Philip Lepoutre
Before clouds collapse into rain, they can actually reach an incredible mass of 500,000 kg (1.1 million pounds). For perspective, it’s like having 12,500 heavy pianos floating around in the air.

by Philip Lepoutre

Science Editor

For some, there is nothing better than a rainy day to make you feel so full of joy you want to break out in song and dance as Don Lock- wood did in the 1952 film Singin ́ in the Rain. “I’m singin’ in the rain, just singin’ in the rain, what a glorious feeling and I’m happy again!”

However, movies are not always true to life and many people have a much more difficult relationship with the rain. Belgium has always received heavy rain. In fact, it rains so much in Belgium that hundreds of artists and painters from all around the world come to Belgium to create works of art portraying it. Famous examples include Keiko Tanabe, a Japanese painter who lives in the United States and the world-renowned Leonid Afremov, a master of the palette-knife technique. Not only are they deeply intrigued by Belgian culture but also by its weather that stirs up debates all over the world.

Rain is formed when the energy from sun rays heating the ocean surface cause water to change from a liquid to gas state in a process called evaporation. When the clouds eventually cool down they turn back to a liquid state near dust and other particles. The small droplets then become visible and start to be attracted to other neighbouring molecules, behaving like magnets. As more and more droplets merge together, their combined mass becomes too large and hence falls back down as the rain we know all too well. However, before clouds collapse into rain, they can actually reach an incredible mass of 500,000 kg (1.1 million pounds). But how do clouds manage to support so much weight in the first place, seemingly defying gravity? In fact, even though they have an immense combined weight, this weight is usually spread out over a few kilometres, allowing each cubic meter to weigh less than 1g.

When we look more specifically at Belgian weather, the first indicator, which may explain this bad weather, is Belgium’s location near the North Sea. According to a study by the Royal Belgian Institute of Meteorology in 2019, winds that come from the North to the East of Belgium outnumber any other direction. As these winds pass above the sea, they pick up water molecules from the ocean and become humid.

But, if we look at the average rainfall in Belgium, another question arises: the area with the most rainfall is the Ardennes, despite being located much farther from the ocean than the majority of places in Belgium. Why is that so? This is caused by the fascinating behaviour air masses display when coming in contact with mountainous landscapes. As wind packed with water molecules travels, it picks up more and more molecules as it goes, but when it reaches a large obstacle like a mountain, it is forced to climb up and condense, releasing all of its moisture into the clouds. These clouds will then release the accumulated moisture onto one side of the mountain for the most part. As this happens, the dried-up wind travels to the other side, picking up any moisture that is present.

This behaviour is known as the “Rain Shadow”, an effect first discovered in 1982 by two Argentinian scientists.

The second clue as to why Belgium finds itself under constant rainfall lies in weather maps that reveal the dynamics of our atmosphere. There are very strong currents of air directed to the North Western European continent whose origins lie in the Atlantic Ocean. These strong currents are called “jet streams”. They are very fast flowing air currents, usually at around 15km in altitude, that appear due to the union of two air masses with radically different temperatures. Hence, the larger the temperature difference between the two air masses, the faster the “air river” will flow.

As it turns out, jet streams are not only present on Earth, but also on other planets of our solar system like Jupiter and Saturn. Jet streams are very frequently used by commercial airliners to reduce travel time. By flying in a jet stream, planes travelling from West to East get a significant boost from the tailwind, which saves time and fuel. Conversely, planes flying in the opposite direction lose time and expend more fuel flying against the jet stream so pilots usually adjust their flying altitude to avoid them. But what does this have to do with Belgium’s weather? As jet streams flow from the Pacific to Europe, they bring in warm air, filled with water molecules. As they reach Belgium, they increase the air humidity and hence also increase the chance of rainfall.

So next time you open your umbrella to go outside, look up the raindrops falling and remember that they travelled huge distances just to arrive where you are, travelling through fast moving jet streams from the Atlantic just to end up in clouds where they will spend their last moments, packed with other raindrops, ready to fall as soon as the cloud gets too heavy.