Answer:
"with all this rain, we will have to build an ark"
Step-by-step explanation:
Allusion is a figure of speech that refers to a place, an event, a person or even an item. They may be real, or imaginary. Referring to things that are fictitious, referring to myths, referring to religious manuscripts and even as much as folklore.
The references can be direct, and some others, indirect, it doesn't matter. Allusions are a way to bring the readers into the piece being read since a lot of people just read without necessarily being in the piece.
These being said, the allusion in the quoted text is
"with all this rain, we will have to build an ark"
And it is a reference to a religious manuscript.