It happens just like fires. Drought increases because it is self-propagating. And this additionally generates an increase in the rainfall deficit. This is pointed out by the European Research Council (ERC).
It is not like other extreme weather phenomena, such as hurricanes or winter storms. Droughts affect humans in most climatic zones of the world. It ranges from the arid steppes of the Sahel to the rainforests of the Amazon. They are intensifying in many regions as a result of global warming. It is described as “the next pandemic”.
Dry land and less rain
Rainfall deficits eventually manifest themselves as dry soils. The land surface, however, also plays a very active role in rainfall generation. Why? Because it provides moisture to the atmosphere through evaporation. What happens during a soil drought when much less water evaporates than normal? The drought increases because it is self-propagating. There is less moisture for precipitation, not only locally, but also downwind.
The study is published in Nature Geoscience. It is led by the University of Ghent (Belgium). It analyzed the 40 largest droughts in recent history. Up to 30% of the rainfall deficit may be caused by this self-propagating drought.
Dominik Schumacher is first author of the study. He says: “In essence, droughts behave similarly to wildfires. Fires spread downwind by igniting more and more ‘fuel’ in their environment. Droughts do so by reducing their own rainfall supply through drying out the land surface.”
The authors find self-propagation strongest in subtropical drylands, such as in Australia and southern Africa. There the limiting effect of low soil moisture on evaporation is strongest.
Drylands are projected to expand in light of climate change. So the self-propagating nature of droughts may lead to even larger events. This would further exacerbate water scarcity, as well as the associated socioeconomic and environmental consequences.