This is the 5810th most frequent Polish word.
zalewają
"Zalewają" means "they flood" or "they pour over."
In this sentence, 'zalewają' metaphorically describes rain clouds covering or dominating the presence over the city, implying an overwhelming quantity.
Deszczowe chmury zalewają miasto.
Rain clouds are flooding the city.
Here, 'zalewają' signifies the excessive bombing or inundation of advertisements in a metaphorical sense.
Reklamy zalewają naszą skrzynkę pocztową.
Advertisements are flooding our mailbox.
In this context, 'zalewają' refers to an actual physical scenario where water overflows its boundaries.