Coastal cities increasingly face compound flooding risks due to sea-level rise and intensifying storms. This study systematically evaluates the synergistic regulation of coastal hydrodynamics by mangrove vegetation and intertidal topography as a nature-based solution (NbS) for coastal defense. Based on the Delft3D Flexible Mesh (FM) system, we simulate tidal and storm surge scenarios in two contrasting shorelines in Shenzhen, China, the naturally evolved Xiwan Mangrove Park and the engineered Bao'an Airport coastline. Results show that intertidal topography plays a dominant role in attenuating flow velocity, while mangrove vegetation becomes the primary factor in reducing peak water levels during extreme events. A functional shift in mitigation zones occurs, from mid and low tidal flats under tidal conditions to high flats during storm surges, driven by increased inundation and canopy engagement. Additionally, a clear design threshold of 600 m planting width is identified, beyond which additional vegetation provides diminishing returns due to the complete submergence of mangrove vegetation. These findings underscore the complementary roles of topography and vegetation and offer actionable guidance for optimizing NbS strategies in site-specific, climate-adaptive coastal management.

As the world grapples with the profound impacts of climate change, water scarcity has become a pressing issue. However, there is a shortage of in-depth research on the trade-offs between water resource dependence and the economic, ecological, and social needs of arid and semi-arid regions like Lanzhou, China. Flower cultivation in Lanzhou relies heavily on the Yellow River, often overlooking the potential of natural rainfall. Here we first calibrated a water balance model through artificial precipitation experiments in a Soil and Water Conservation Demonstration Park in Lanzhou. We then developed a multi-objective optimization model to balance the cost-benefit considerations of various plausible measures across economic, ecological, and social dimensions in the searching for solutions that are more adaptable to climate change and local development needs. Model simulations show that the solutions we designed can effectively manage water-shortage days, significantly reduce Yellow River water extraction, and improve cost-effectiveness, meeting 66%–80% of water needs for flower cultivation in the studied park. The findings highlight the potential of rainwater collection and utilization solutions to mitigate water scarcity in arid and semi-arid cities, thereby enriching water resource management.