Too dry spring in the north: the drought that remains

Once again, too little rain has fallen. A dry summer is looming in northern Germany. There is much to suggest that we will have to get used to it.

This is what the future will probably look like: Field that needs to be irrigated Photo: Julian Stratenschulte/dpa

April 2020 was the sunniest April since records began. According to initial evaluations by the German Weather Service (DWD), it is the third driest and seventh warmest since regular measurements began. At the same time, climate statistics show that Germany experienced the twelfth consecutive April that was too dry. If climate researchers’ models are anything to go by, this is likely to continue for the next few years.

According to calculations by the Helmholtz Centre for Environmental Research (UFZ) in Leipzig, northern Germany is facing a paradoxical development: although there will be slightly more rain over the year, the low water levels in the rivers will fall and the periods of drought will become longer. This is the result of a UFZ study on the "Effects of global warming on hydrological and agricultural droughts and floods in Germany".

In it, researchers combined four different hydrological models with five climate models and calculated a warming of 1.5 degrees, two degrees and three degrees respectively compared to the reference period 1971 to 2000. In this way, they can determine how different climate targets will affect which region. The inclusion of hydrological models is a special feature here. "You can estimate what happens in the ground," says Andreas Marx, one of the study’s authors.

The international community agreed on a maximum global warming of 1.5 degrees at the 2015 climate conference in Paris. Previously, two degrees was the norm – but three degrees is more likely, based on past experience and promises, says Marx.

Droughts increase in every scenario

"Under all warming rates, droughts increase," Marx says. "But at 1.5 or two degrees, the changes are much smaller than at three degrees." While a warming of 1.5 degrees Celsius would lead to slightly more frequent low water only in Lower Saxony and Bremen, at two or even three degrees, shipping would be at increased risk from low water in all five northern German states.

The situation is similar for dry fields. At 1.5 degrees, the annual drought would last 13 percent longer in both Schleswig-Holstein and Lower Saxony, and percent longer at three degrees. The fact that the soil contains less water despite increasing precipitation over the year is due to higher evaporation.

Anyone who wants to see how global warming is likely to affect them in detail can do so at klimafolgenonline-bildung.de, a website of the Potsdam Institute for Climate Impact Research. Here, the future can be seen for certain regions and areas by including various scenarios – based on the reference period 1981 to 2010. We choose the probable scenario for weak climate protection and as forecast periods 2021 to 20 to 2100.

According to this scenario, groundwater recharge in the Harz Mountains and a corner of the Weserbergland would decrease by at least 30 millimeters between 20, and between 20 the same would apply to the Luneburg Heath and southern Lower Saxony.

In our chosen scenario, there would be more days without precipitation in 2021 to 2050 throughout northern Germany compared to 1981 to 2010 – with over plus 20 days especially in southern Schleswig and a small part of southern Lower Saxony. 2071 to 2100 there would be more than 20 additional dry days almost everywhere.

Hot and humid around Bremen

Two to four more hot days would occur south of Bremen by mid-century, and more than twelve additional hot days by the end of the century south of Bremen and in Munsterland. More humid days must be expected in Bremen, East Frisia, Cuxland and in Munsterland.

The longer wet and dry periods would have consequences for agriculture. Yields of winter wheat, potatoes and silage corn would decrease only in Schleswig-Holstein by mid-century, and in all of northern Germany by the end of the century.

In southern Lower Saxony in particular, many trees would suffer from the increasing drought, especially the beeches. In the case of oaks, on the other hand, which cope better with drought, yields could even increase in the Harz Mountains by 2050. In large parts of northern Germany, pine could gain by the end of the century.

Danger for the forest

Caution is needed in drawing these conclusions, however. "Extreme events are not well represented by the models we currently have," warns UFZ researcher Marx. What is lost in them, for example, is an accumulation of dry years. "I’m surprised by the drought we saw in 20," Marx says.

While field crops can benefit immediately from a good year, forests are a different story. In addition to direct damage from prolonged water shortages, trees become vulnerable to pests and wildfire. Entire forests can fall victim to this. "You can’t pull up a new forest every year," says Marx.

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