Answer: B. Zeitoun is realizing the likelihood of flood casualties.
In this passage, Zeitoun reflects on the difference between the situation in his neighborhood, and that of other parts of the city. He thinks about how his neighborhood was miles from the closest levee, so the water rose slowly and it was unlikely that anyone had died. However, in the neighborhoods closer to the breaches, it is likely people had died. He is realizing that the likelihood of flood casualties near the breaches is high.