Does urban green infrastructure lead to equity issues for flood vulnerable areas? A case study in an urbanized polder area

Abstract

Vegetation can help cities to mitigate and adapt to flood risks as urban green infrastructures (UGI). However, the spatial equity outcomes of UGI in flood regulation among vulnerable areas are not well understood. Taking an urbanized polder in Kunshan, China as a case, our study estimates flood regulation efficiency (FRE) by the actual evapotranspiration, infiltration and increased runoff, then flood vulnerability index (FVI) from physical and social characteristics is evaluated to detect variations in FRE among blocks with different levels of flood vulnerability. The findings revealed that UGI achieved greater FRE under rainfall with lower intensity and longer intervals (S1 = 2.61; S2 = 5.88) than higher intensity and shorter intervals (S3 = 0.96), as the latter showed lower infiltration during rainfall and less evapotranspiration rate after rainfall. Public service areas obtained the highest mean FRE whereas self-built housing areas had the lowest. Statistical analysis revealed negative associations between FRE and FVI across all rainfall conditions (slope = −11.61 to −4.06, p < .05), and showed a stronger bias towards groups with less flood vulnerability (Gini = 0.87). This inequity outcome was derived from social (Gini = 0.72) other than physical vulnerability (Gini = 0.43), which was further proved by significant difference of FRE between high and low social vulnerability levels (p < .05), especially between self-built and commodity housing areas. This study provides a process-based methodology framework to promote equitable UGI for mitigating and adapting flood risk in urban communities.