Which city has the most severe projected water supply problems?

The most severe projected water supply problems are often linked to factors such as population growth, climate change, and over-reliance on limited water resources. In the case of Flagstaff, it faces unique challenges due to its reliance on a primarily forested watershed, which is highly sensitive to drought and other climate changes. Increasing temperatures and decreasing snowpack can lead to diminished streamflows and other water availability issues, exacerbating the city's water supply difficulties. Additionally, compared to larger metropolitan areas like Phoenix and Tucson, Flagstaff has limited water supply options to support its growth and any potential increases in demand, contributing to its more acute water supply concerns.

In contrast, larger cities may have a more diversified water supply portfolio and resources, allowing them to manage drought and demand more effectively. As a result, Flagstaff's particular geographic and climatic conditions, along with its water supply dependencies, are key factors that contribute to its status of having the most severe projected water supply problems among the options provided.