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Cities increasingly face challenging regulatory requirements for their aging sewer systems. Population density and can contribute to changes in impervious cover that limit infiltration, expedite the rate of water drainage, and overwhelm the conveyance system. This work presents a method for applying high-spatial resolution population-based scenarios to pre-existing stormwater models. We explore the impact of two long-term population growth scenarios for the Pittsburgh region. We find that an extreme 79% growth in population results in 24% increase in impervious area and an 11% increase in total overflows. In contrast, a moderate 15% rise in population yields an 8% increase in impervious area and a corresponding 5% increase in overflows. As the relationship between population growth, impervious area, and total sewer overflow is non-linear, it is of critical importance to understand neighborhood-level changes. Our work fills a critical scalar gap for adding robustness analysis to these projections.