The east coast megalopolises faces serious problems because of

Water Shortages

Explanation

Water scarcity is the lack of sufficient available water resources to meet water needs within a region. It affects every continent and around 2.8 billion people around the world at least one month out of every year.

it is very hard for the climatologists to precisely predict how will the global temperatures be changing so there's lots of models, some of which differ significantly, this is due to multiple factors, and probably the most important is the human activity.

humans have been a key factor in climate change around the globe since the start of the industrial revolution, and in the past few decades the consequences are becoming more obvious. there's lots of emission of pollutants in the atmosphere as well as changing the environment on the surface itself, so it's really hard to predict how will that go in the future because there's some countries that are reducing the damage and are going towards green energy, while others are stubbornly continuing with pollution and damages to the environment.

answer; the correct answer is chemical: