Climate change in Baden-Württemberg: It recently rained so little in Calw – News

It hasn’t rained much in Calw in the past few days. Is this drought unusual for the time of year? Current and historical data on rain and temperature provide the answer – also on the connection with climate change.

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Is the weather in Calw (zip code 75365) normal today? Is it too hot or too cold, too dry or too humid for the time of year? The answer comes from data from the Renningen-Ihinger Hof weather station (precipitation) and the Stuttgart (Schnarrenberg) station (temperature).

Temperature today: up to 29.5 °C. That’s unusually warm.

What is considered “normal” is the long-term mean measured at this station. “Unusual” are values ​​that clearly deviate from this. We compare the current weather data in Renningen-Ihinger Hof with the periods 1961 to 1990 and 1991 to 2020. The comparison with 1961 to 1990 shows long-term changes in the climate – partly as a result of man-made climate change. In many places, climate change has accelerated in recent years. This is shown by a comparison with the period 1991-2020.

The colored line shows the daily maximum temperatures for the past few weeks to date (highlighted as a circle). If the line is above or below the normal gray area, it is unusually warm or cold. We show the normal range because it is more robust to random fluctuations in the weather than the pure mean (dashed line) comparison. The same comparison can also be made for the lowest temperature measured on a day:

Unusually warm and cold temperatures are outside the normal gray area in our model. The following table shows how large the fluctuation can be on one day over the decades:

How much it is currently raining – and what would be normal

Rain in the last 30 days: 14 mm. That is unusually little.

Precipitation can also be compared with long-term measurements. However, the amount of rain on a single day varies much more than the temperature. Therefore, this diagram not only shows the rain on one day, but each point represents the sum of the last 30 days. The same applies here: If a point is outside the gray normal area, it was unusually wet or dry in a long-term comparison.

What climate change has to do with it

There can be outliers even without climate change. The fact that the climate is changing only becomes apparent in long-term trends. We can not only calculate whether it is getting warmer overall, but also whether it is getting hotter more often in summer or colder and colder less often in winter. Such a tendency can be checked, for example, on so-called hot days, summer days and frosty days. The days are defined as follows: 30 degrees or more are measured on hot days, 25 degrees or more on a summer day, and the temperature falls below freezing on a frosty day.

Hot days from 30 °C: So far there have been 23 since March. The month in which these days occur varies from year to year, but since 1961 the number has increased.

How many days like this have happened since March? How many were there in total in the past summer months?

The trend line shows the development since 1961. If, for example, the number of hot days has increased over the decades, this indicates increasingly frequent and longer heat waves. On the other hand, if the number of frosty days falls, the weather tends to be milder in the colder months.

The following graphic shows whether the current year has been comparable to previous decades:

The right column represents the number of hot days measured since March/September. For comparison, the average values ​​for the years 1961-1990 and 1991-2020 can be seen on the left. The shaded gray zone shows the normal range for most of the years in the respective comparison period.

The “climate strips” diagram shows that climate change is causing Calw to become warmer overall.

Each climate strip represents a year. Blue means the average temperature that year was below the long-term mean from 1961 to 1990. Red means that the year was warmer. The stronger the red, the warmer the year was in comparison. These increasingly hotter and hotter years are becoming more frequent in recent years.

So far, climate change has had less of a clear impact on precipitation. In Baden-Württemberg it rains a little less overall in summer, although drought and heavy rain increasingly alternate. Winters tend to be wetter.

sunshine hours

The number of hours of sunshine is important for the well-being of many people. This is how often the sun last came out in Calw:

How much and how long the sun shines also varies depending on weather developments, but according to the current state of research has little to do with climate change. In the past, long-term changes were mainly caused by cleaner air.