Was looking at the news reports about the floods in UAE and wondering why a desert so vast with little to no vegetation just absorb all the rainfall?
In: Planetary Science
When something is very dry, it can get compacted and not have any space or cracks for water to soak into. It acts more like concrete than sand.
When you put dirt into water it turns into mud because the Dirt and Mud became one. When you put sand into water it remains sand, the sand is at the bottom of the water and the water is on top of the sand. Sand Sinks. Dirt and water combine and make Mud.
Sand does do a good job of draining water away. It’s one reason why FL rarely has severe floods from rain (floods from storm surge are another matter).
However, enough water coming down fast enough can still overwhelm how fast sand can drain away water, leading to flooding.
Cities are also covered not entirely by sand, but by lots of roadways, sidewalks, buildings, parking lots, and other paved space that doesn’t drain water well at all, relying on storm drains to divert water away.
Many cities in the UAE, Dubai especially, have grown exceedingly fast and without thought to central planning and utilities, so the storm drain system (as well as the sewage system in general, plus things like roadways and traffic management) are woefully inadequate.
On normal days they ride the knife’s edge of catastrophic failure. Throw in an actual natural disaster and there’s no chance they can handle it well.
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