Flooding remains the most frequent and damaging natural hazard worldwide, and green infrastructure (GI) has been widely promoted as a nature-based strategy for flood mitigation. However, the scarcity of long-term event-based flood databases that integrate intensity, duration, and frequency limits understanding of large-scale flood dynamics, introducing uncertainty in future projections and the development of effective GI strategies.

This dissertation develops a national-scale analytical framework integrating event-based hydrological analyses to understand and project future flood risk. Building on this framework, the study further examines how GI composition and configuration differentially regulate flood dynamics across future risk trajectories. The dissertation consists of three major components: (1) identifying flood risk classes across the contiguous United States based on the full intensity-duration-frequency spectrum of flood dynamics; (2) examining the dominant climatic, land-cover, and biophysical drivers that shape divergence among flood risk classes and projecting their evolution under coupled climate and land-cover change; and (3) exploring how GI composition and configuration influence flood occurrence, intensity, duration, and frequency across watersheds with contrasting future risk trajectories in the Great Lakes region.

Results reveal a pronounced east-west divergence in future flood risk trajectories, which intensifies under high-greenhouse gas emissions (SSP5-8.5) and regional-economic development (A2) pathways. Flood risk declines across the western and interior United States as sustained warming reduces long-term snowpack accumulation and associated snowmelt-driven events. In contrast, risk increases across the Northeast, Southeast, and Midwest, driven by intensifying rainfall and accelerating urban development. Land-cover management provides effective near-term potential to mitigate risk. However, by the late century, climate factors dominate, rendering land management alone insufficient to offset rising hazards. Under these divergent future risk trajectories, the regulatory effects of GI are dimension-specific (i.e., intensity, duration, and frequency) and exhibit an evident heterogeneity across watersheds. In watersheds with stable flood risk classes, increasing GI coverage is effective in reducing flood occurrence, while in watersheds experiencing higher future risk, spatial reorganization of GI patterns is more effective.

These findings demonstrate that flood risk across the contiguous United States is increasingly governed by region-specific and temporally evolving climate-land interactions and highlight the need for adaptive GI planning and design strategies that respond to divergent hydroclimatic environments and risk trajectories. These strategies should be implemented in coordination with complementary flood management approaches to maintain long-term effectiveness.