Self cleaning street - photo

Self cleaning street in South Korea. Anyone know what's going on here? Why is this needed to supplement rain? Cooling?

https://diqn32j8nouaz.cloudfront.net...ing_street.jpg

Previously:

https://www.homemadetools.net/forum/...3661#post99717
https://www.homemadetools.net/forum/...397#post107280

That's for cooling.
The city of Daegu, South Korea is surrounded by mountains and because of that it suffers from severe urban heat island effect a lot.
So they implemented what you see in that photo.