An integrated planning framework for assessing stormwater runoff and non-point source pollution impacts of vacant-lot buyouts and green infrastructure

Structural engineering solutions alone have proven limited in reducing flood risk, increasing interest in non-structural approaches such as land-use planning, buyouts, and green infrastructure (GI). This study evaluates the stormwater runoff and non-point source (NPS) pollution impacts of vacant lot buyout policies in Galveston County, Texas, a hurricane-prone coastal area along the Houston Ship Channel. Using the Dynamic Conversion of Land Use and its Effects (Dyna-CLUE) model, we projected vacant lot changes from 2022 to 2037 based on the most recent validated land-use dataset and a standard 15-year planning horizon. Buyout priorities were assigned at the parcel scale using floodplain location and inundation depths from Hurricanes Ike (2008) and Harvey (2017). Hydrologic and water-quality impacts of converting acquired parcels to GI were assessed using the Long-Term Hydrologic Impact Assessment Model (L-THIA) across three scenarios. Results indicate that vacant lot area is projected to decline by more than 1300 acres between 2022 and 2037, with land-use change estimated to increase runoff depth by 1.84 in. (6.4%) and chemical NPS loads by 24,429.23 tons (9.4%). GI implementation is estimated to offset these increases, reducing countywide runoff by 0.17–0.91 in. (∼9–50% of the projected increase) and lowering chemical pollutant loads by 1795–9362 tons (∼7–38%) by 2037. In the high-priority buyout category, GI transformation is estimated to yield $78.75 million in avoided flood losses. These findings suggest that strategically prioritized buyouts, coupled with GI transformation, can provide scenario-based rainfall-driven reductions in land-use-related hydrologic and water-quality impacts and support long-term flood-resilience planning.