Drought, climate change and land management
In many countries, also in Germany, it is getting hotter and drier, and the dry season in particular is getting longer and longer. But where does this come from? Many associate the drought only with climate change. Yes, that's true, but that's only 50% of the story. To understand what the other 50% is due to, we asked Stefan Schwarzer.
Summer drought and little rain
betterSoil: In eastern Germany, as in many other areas and countries, it is very dry. Why is there so little rain? What are the causes of the summer drought?
Schwarzer: There are varied reasons for this. Partly this is due to poor, because of sandy soils, which cannot hold the water very well. Then there are naturally regions which receive less rainfall. There are clearly effects of human induced climate change. But and this is especially important to know, droughts are often not God-given, but have a human influence through bad land management practices. Overgrazing, overuse of the soil through plowing (remember the Dust Bowl in the US in the 1930s!), drainage systems all add up to an interruption of the natural water cycle. Thus, 50% of the drought conditions in eastern Germany could eventually be attributed to bad land management practices – which is good news, as we can change these through regenerative, water holding agricultural, forestry and water practices.
Where is it dry, where wet?
betterSoil: Why are some parts of Germany very dry and some parts very wet?
Schwarzer: The distribution of rainfall depends very much on a) the distance to the ocean (the further away, the less rain) and b) the topography and c), as we saw above, on vegetation, forests. Mountains block the clouds, force them to lift which increases the chance of precipitation.
betterSoil: Summers are becoming very hot also in Germany. What can be done to reduce the temperature? What can soil do to bring down the temperature that we feel?
Schwarzer: Vegetation not only recycles the water but transports it through so called “flying rivers” across thousands of kilometers further inland. The phase change from liquid water into water vapor is an energy intensive process, which explains why in hot temperatures we prefer standing or sitting below a tree or walking in a forest: Vegetation cools the environment! A large tree in the temperate zone can transpire up to 500 liters of water on a sweltering day, cooling its environment with the equivalent of 10 air conditioners running full power for the day.
Cooling soils and vegetation
betterSoil: Why is it warmer on a bare field than on a vegetated area? Why is it especially important to leave a vegetated area to cool the environment in the summer?
Schwarzer: When the sun rays hit a vegetated area, 80-90% of its energy is transformed into latent energy – the energy then stored in water vapor. On a bare field, 70-80% of the sun’s energy is transformed into sensible heat, increasing the ambient air temperature, as well as a larger part into warming the soil. Now, instead of transferring that latent heat into higher parts of the atmosphere, where it then condenses, creating clouds and enabling the dissipation of parts of that freed energy in outer space, the heating up of soil and now atmospheric ground layer emits an increasing amount of long-wave radiation, which hits in the atmosphere the greenhouse gas molecules, increasing the GHG effect. And, without water (vapor) rising into the atmosphere, there are no clouds, thus no rain.