Experiment – Dry soil is water repellent – Meteo

In many regions of Switzerland it is dry and there is no precipitation. Rain is desirable, but not too much at once.

This article was inspired by a tweet by Dr. Rob Thompson, also known as «Dr. Rainman’, who works at the English University of Reading. With an experiment, he pointed out that it is better not to have too heavy rain showers during a dry phase, because these would not seep away well in the dry soil, but would run off on the surface and possibly lead to flooding.

We conducted this experiment on Swiss soil in the Mittelland. It becomes clear that the water seeps into the ground much more slowly on the dried-up lawn than on the green lawn. The technical term for this is hydrophobia.

It has not been scientifically clarified why the dry soil is water-repellent. They are probably organic substances that are not soluble in water and/or contain fatty acids and waxes. These prevent the water from penetrating the ground and it only seeps slowly through cracks or crevices in the ground.

To alleviate the dry soil, it would only have to rain moderately over a long period of time. Because as soon as the ground is moistened, the rain can seep away better.

Sources:
Florian Jehn: Properties of biological soil crusts before and after mechanical disturbances and their influence on hydrophobicity in Sekule / Slovakia (2014).

Matthias Kuhnert: Quantification of surface runoff and erosion on soils with hydrophobic properties, dissertation at the University of Potsdam (2008).