Parched

The term “Heißzeit” (hot age) hit the headlines nationwide in Germany in 2018 and was choosen as “word of the year”. It is a wordplay on the German term “Eis­zeit” (ice age). The summer had indeed been unusually warm – with an average of 10.4 degrees Celsius, 2018 was even the warmest year since the beginning of Germany-wide weather records in 1881. For farmers in particular, however, the biggest problem was not the heat, but the extreme drought that began in June.

“Our measuring stations in the meadows and forests of the Eifel as well as on a field in Selhausen near Jülich recorded an annual average of up to 23 per cent less precipitation than usual in 2018,” reports Dr. Alexander Graf from the Institute of Bio- and Geosciences (IBG-3). The three stations belong to the Helmholtz initiative TERENO, a network for earth observation stretching from the North German lowlands to the Bavarian Alps. The researchers measure how the surface of the land and the atmosphere exchange substances and energy – from precipitation and evaporation to carbon dioxide.

Compared to the Jülich locations, rainfall in other German regions was even lower (see chart here). According to the German Drought Monitor, summer and autumn have never been drier than in 2018 compared to the average since 1951. The drought continued even after the great heat had passed in September: the peak of the strain on the soil was not reached until early December as the soil and groundwater systems have a delayed reaction to the absence of rain. “The 2018 drought is still in the system,” says Graf.

Poor starting conditions

“At the beginning of 2019, soil moisture was significantly lower in most regions than in the previous year and so were groundwater levels. If it continues to rain too little this year, the situation in the affected areas could worsen further. Some consequences become apparent later on: in forests, for example, such weather events can lead to pest epidemics years later.”

According to Alexander Graf, the biggest loser of the 2018 drought was the climate: “Every summer like the one in 2018 is a lost opportunity for our biosphere to reduce the carbon dioxide load in the atmosphere,” says the Jülich expert. A rule of thumb is that an area that evaporates less than usual also absorbs less carbon dioxide than usual – either because the plants have dried up anyway or because they close their stomata in the leaves and perform less photosynthesis, in which sugar and oxygen are produced from carbon dioxide, light and water. This means that the plants do not grow as well and absorb less carbon dioxide. More CO₂ in the atmosphere, however, intensifies the greenhouse effect and thus advances global warming – and as a result, climate change. Global warming, in turn, means more drought on average – a vicious circle.