ABSTRACT Based on field experiments and modeling in southwestern China, water storage layers increase annual runoff reduction by 12–25% and reduce the optimal runoff curve number from 96 to a range of 88–93. Green roofs play a key role in urban stormwater management. The runoff curve number (CN) model is commonly employed to estimate the impact of green roofs on regional runoff reduction. However, significant variations in runoff reduction rates among different types of green roofs preclude the use of a generalized runoff CN for accurate estimation. This study evaluates the runoff reduction performance of different green roof types through field experiments in a residential area in Southwest China, using water balance and CN modeling. Green roofs with a water storage layer increased annual runoff reduction by 12–25% compared with traditional designs. Optimal CN values were identified: 95 for traditional extensive, 97 for intensive, and 88–93 for storage-layer green roofs. Green roofs with a water storage layer contributed an 8–12% increase in annual runoff reduction in the study area. The findings provide essential theoretical and data support for determining CN values and assessing the effectiveness of green roofs with varied structures in stormwater management.
Wang et al. (2026) studied this question.