Perspectives – not perfection – after silent revolution in Meteorology

Silent revolution

In the more than forty years that Professor Bert Holtslag has been active in meteorology, he has witnessed a silent revolution in his field. "Being able to predict the weather has been a long-held dream for humankind. Weather proverbs are just one example of this, although – contrary to what most people think – many of them are just folklore. The physical models, on the other hand, started a revolution. Today's seven-day weather forecast has roughly the same quality as the three-day forecast forty years ago, thanks to better computers, satellite images and measuring tools, and due to a better understanding of how the atmosphere works," according to Professor Holtslag's farewell entitled 'Atmospheric dreams and perspectives', which delivered on October 10.

The urban heat island effect

Thanks to our improved knowledge, we also have a better understanding of mankind's impact on the atmosphere, both in general and specifically as a result of land use and urbanisation. This is often very different from what people assume. "Urban expansion in the Netherlands and elsewhere can have warming effect on the environment. In Wageningen, we were able to determine that winds from the southeast would cause a temperature increase of 1°C in the rural area near the city, purely because the wind was pushed over the warmer city to the measurement site. And it is not unusual to see a 5°C temperature difference between urban and rural areas. In large cities such as Rotterdam, this urban heat island effect can be as high as seven degrees or more. This can seriously damage the quality of life in a city, as last year's record high temperatures demonstrated. This is in addition to global warming caused by the enhanced greenhouse effect," explains Professor Holtslag.

Detailed weather forecasts can be extremely useful for people living in cities. "The weather forecasts we tested for Amsterdam with a resolution of just 100 metres are already amazingly detailed. This could help us provide pedestrians and cyclists with the coolest route through the city on a hot day. When combined with an air quality forecast, such as for ozone, we can also advise people on the cleanest route to take."

Weather and climate myths

Professor Holtslag has had to debunk his fair share of weather and climate myths throughout his career. For example, many people think that hail cannons are effective, that we can make it rain in a specific area, or that we can use geo-engineering to stop climate change. "These are all myths," says the professor.

Others believe that the sun is the driving force behind global warming. Our measurements do indeed confirm that the amount of solar radiation that reaches the earth's surface has increased by more than 20% since the late 1920s. Wageningen's series of solar radiation measurements are some of the oldest in the world. "But this isn't caused by the sun," says Professor Holtslag. "Rather, it's caused by the fact that our atmosphere has become considerably cleaner over the past ninety years and that there are fewer and more transparent clouds."

Perspectives

In addition to urban applications, detailed weather forecasts on a smaller scale can be used to create more reliable forecasts for the production of solar and wind energy. Despite the occasional objections to wind turbines, these machines can be extremely useful on land to prevent night frost, particularly when fruit trees are in bloom.