There is an old country saying that rain in July rules out a good harvest. There is hardly any other industry that is as dependent on the weather as agriculture. Interesting facts about Europe’s great weather makers.
The Icelandic Low – wind and rain
Rough landscape, wild ponies, hot springs, unpredictable volcanoes – these make Iceland what it is. An island which, thanks to its geographical location, influences the weather throughout Central Europe. And that’s not all: Iceland’s weather has made world history. Strictly speaking, the French Revolution did not begin in Paris in 1789, but six years earlier in Iceland with the eruption of the Laki: one of the largest documented volcanic eruptions in the world. The large, viscous ash cloud that formed during the eruptions moved towards Central Europe and reduced solar radiation levels there for several years. Temperatures dropped. A whole succession of cold summers with catastrophically poor harvests set in. Hunger rebellions broke out everywhere. In France, people raided the armouries. One of these – on 14 July 1789 – was the Bastille in Paris. The starting shot of the French Revolution.
Even today modern agriculture is still dependent on the weather. However, farmers are now better able to react. A large supply of meteorological data has made things more predictable. Even the smallest changes are continuously recorded and published – thereby making a decisive contribution to successful agriculture. After all, a short rain shower is enough to damage an entire hay harvest. Rain washes valuable nutrients out of the hay. What’s more, it only takes a short amount of time for bacteria and fungi to form, which in the end become part of the harvested hay.
Weather extremes due to climate change
Particularly extreme weather conditions such as drought, hail, storm, frost or continuous rain can cause considerable damage to agriculture within hours, days or a few weeks. Climate change means these could occur more frequently in the future. For example, 68 percent of 131 extreme weather events that occurred around the globe, such as severe thunderstorms in southwestern Germany and northern Italy, have been proven to be caused by climate change. Extreme events are therefore already being influenced by climate change in many cases. For farmers, the agricultural meteorology developed for the industry is therefore becoming increasingly important. It also provides important information on soil temperature and moisture, frost penetration depth, evaporation, dew and leaf wetting. Armed with this information, farmers can choose the best time for their work: from tilling the fields to plant-health measures, fertilisation, irrigation and harvesting.
To this day, Iceland continues to affect the quality of harvests throughout Central Europe. This is because Europe’s largest low pressure areas develop in the extreme northwest: the Icelandic Lows. When the sun heats up the ground and the layers of air above it, the warm air rises. The air pressure at the top rises, while a low-pressure region forms at the bottom. As it rises, the warm air cools down again. The result is that it can no longer hold the water vapour it contains. The invisible vapour forms visible clouds; rain showers follow. Weeks of rain, deep grey clouds and wind are then common. And a poor, rainy harvest is often the result.
Bright sunshine – the Azores High
A high pressure system is the exact reverse of the low pressure system. Both are directly connected and together they shape our weather. In the high pressure system, the air masses sink and warm up. Clouds disperse, the sky is blue and the sun shines. There are large areas of high and low pressure around the world, which mesh together like gears and can determine weather patterns over long periods of time. The counterpart to the Icelandic Low is the Azores High. If it stretches to Central Europe in the summer, we see plenty of sun.
Sandy beaches, deep blue sea, lots of sun, exotic and colourful – this is the image these nine small Portuguese islands conjure up. And that’s how they are. Sometimes. Because things often look different here where the big highs for the whole of Europe emerge. Storms, heavy rain, floods and landslides caused by masses of water – none of these are uncommon. No wonder, given that the Azores lie exactly between the USA and Southern Europe in the rough Atlantic Ocean. Just the right place for exciting weather: strong winds and rainfall alternate at breakneck speed with blue skies and sunshine. In the Azores, humid ocean air is pushed against the mountains, where it rises and condenses. Dense rain clouds form. And after the rain, the beautiful landscape of the islands shines again in the sunlight.
But why do Europe’s largest high-pressure systems develop over the Azores in particular? Part of the answer lies in the Coriolis effect. Warm air rises at the equator. But the earth is rotating. A point on the equator covers 40,000 kilometres a day, while a point in Frankfurt, Germany, only manages about 25,000 kilometres. So the farther north equatorial air comes, the slower the Earth seems to rotate below it. The air hurries ahead and is pushed to the right. Further and further to the north-east until, around the Azores, it loses strength and can no longer go any further. The air now is forced down, since a steady supply is always coming from the equator. Therefore the air pressure rises – a high pressure system is created. Sometimes these are so large that they spread over all of Central Europe, giving us sunny weather – and a good harvest. According to old countryside lore: “July, bright and clear, gives a good harvest year.”