Regional joint regulation mode for flood control in plain cities: addressing extensive heavy rainfall.

Establishing a coordinated flood storage and drainage joint regulation mode for various cities can effectively mitigate the disaster risk associated with extensive heavy rainfall. This study introduces a novel concept of joint regulation of urban agglomeration based on watershed features and spatial topological norms. From the perspective of urban agglomeration, three new modes are proposed to guide flood storage and drainage in plain cities: (1) storing before discharging, (2) discharging before storing, and (3) discharging while storing. The modes aim to facilitate coordination among neighboring cities in an urban agglomeration and enhance the temporal and spatial coordination of flood storage and drainage. Multi-layer tree rules are established to allocate modes to cities based on the spatial characteristics of flood risk, storage, and drainage performance. The fact case proves that the mode has certain practical applicability. There are 35, 151, and 30 plain cities that use DS, DWS, and SD modes, respectively, out of 221 total. Most urban agglomerations employ at least two different joint regulation modes. The multi-layer tree rules for mode allocation presented in this study provide theoretical guidelines for flood management in plain cities across various regions.