What is a mud shower?

Mud rain is rain that contains a high concentration of sand or dust particles. When it dries, cars and windows are covered with sand.

This was the case during the last major episode in France in February 2021.

Where does the mud rain come from?

The soil and sand contained in mud rain can be of local origin or come from very distant regions such as the Sahara. It is when these dust particles come into contact with rain that they combine with water to form what is known as mud. When the rain droplets fall to the ground and evaporate, they leave behind a surface layer of dry mud and sand on the objects on the surface.

Is mud rain harmful to health?

Mud rain poses a health risk to people with respiratory problems, as the fine dust particles settle and can reduce the quality of the air we breathe. The polluted environment makes sensitive people more prone to allergies and irritations, and can lead to breathing difficulties if they are prone to asthma.

To avoid the adverse effects of sand-laden rain, it is advisable to cover the head and face when exposed to it. It is also recommended to clean surfaces exposed to sand and to wash hands regularly.

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What is the impact of a mud shower on crops?

Rich in sulphates, iron, phosphorus, carbon and aluminium, this sludge rain is very beneficial for crops, as it is comparable to a natural fertiliser that can revitalise vegetation. In addition, the iron and other nutrients in the dust can also cause phytoplankton blooms when the dust is deposited in nutrient-poor waters.

However, although sand is an excellent fertiliser for plants and algae, the impact of sand grains against exposed surfaces can damage crops. By clogging the pores of the leaves, the sand reduces photosynthesis and, consequently, the production of food for the plant.

In addition, sand can absorb water from rain before it reaches plant roots, causing plants to dry out. Finally, sand can carry harmful pesticides and herbicides into fields, damaging crops.

Where can you find mud rain?

The origin of mud rain is airborne dust. Mostly originating from the Sahara and the Gobi Desert in North Africa, this micrometer-sized dust is blown by the wind at high altitudes and transported over thousands of kilometres. Transported around the world, this dust has been observed on the Greenland ice cap, but also in France, North America, the Amazon...

Using ice cores from Greenland, scientists are able to trace the history of dust deposits, which appear as layers in the ice. The mineralogy of the dust in the ice allows them to trace the original desert and thus determine the global wind patterns of thousands of years ago.

Photo credit: CC BY-SA 2.0 | https://www.flickr.com/photos/falcon_33/13020374913