How Sponge city policy influences urban design in China—a study from the perspective of parametric design

Sponge city policies in China primarily focus on micro-scale low-impact development (LID) facilities, yet their influence on macro-scale urban design remains insufficiently understood. This study develops a parametric “form – performance” framework that links quantitative policy requirements to key urban morphological elements. The framework integrates automated scheme generation, policy-based runoff calculations, and sensitivity analysis to clarify how stormwater control objectives interact with land-use intensity and underlying surface configurations. Results show that stormwater management strategies depend strongly on development density. High-plot-ratio sites rely more on green roofs to meet total and peak runoff control requirements, whereas low-density contexts benefit more from permeable pavements as a cost-effective alternative. Sunken green space consistently appears as the most sensitive indicator across scenarios, underscoring its disproportionate influence on runoff control. However, the findings also suggest that current policies may inadvertently encourage the overuse of certain high-performance LID technologies, potentially reducing spatial diversity and weakening resilience under extreme rainfall. This study demonstrates the value of integrating policy-based evaluation with parametric tools in early-stage urban design. The proposed framework offers a systematic approach for aligning policy targets with spatial design strategies, supporting more balanced and resilient stormwater management in future sponge city planning.