It is becoming increasingly sunny in the Netherlands. Since the early 1980s, a rising trend of an average of 3.3 percent per decade has been observed. This increase applies to all seasons and is strongest in spring. The main reason is that the air has become clearer, partly due to a reduction in air pollution. At the same time, it has become slightly more common for winds to blow from less sunny directions, mainly from the south and southwest. Otherwise, the increase would have been even greater.

Solar Radiation is Increasing

In the Netherlands, the increase in solar radiation is one of the most pronounced rising climate trends (see image 1). This year has also started off very sunny, and according to expectations, 2025 is on track to become the sunniest year on record, even sunnier than record year 2022. On average, the annual solar radiation is now about 15 percent higher than around 1980. In spring, the increase is strongest at 4.2 percent per decade.

What Causes the Increase in Solar Radiation? 

The increase in solar radiation is primarily due to the fact that the air has become clearer in recent decades. The sun has not become stronger. Possible causes include cleaner air, changes in cloud patterns, such as less or thinner cloud cover, or more frequent occurrences of sunny wind directions. Since the 1980s, various European environmental laws have been introduced to reduce air pollution. As a result, air quality in Europe has improved significantly. Fewer polluting particles in the air means less reflection and absorption of sunlight and thus an increase in the measured solar radiation at the ground.

Research has shown that the amount of cloud cover has increased, but at the same time, clouds have become thinner on average. The ultimate effect of these changes is that they have counteracted the solar radiation trend. The influence of changes in wind direction on the solar radiation trend was not well known until recently. In the past few months, I have researched that.