Impact of different rainfall patterns on flood risk on the urban-rural gradient.

With the high incidence of extreme rainfall, the differences in flooding brought about by the urban-rural gradient (URG) have led to unexpected damage, and rainfall patterns may affect the extent of flooding differences on the URG. Currently, the patterns of dynamic responses of flood risk (FR) along the URG to different rainfall patterns remain poorly understood. In this study, a framework combining coupled hydrodynamic modeling and multi-indicator decision analysis was developed to quantify the characteristics of the dynamic response of flood risk to different rainfall patterns (RFRRP) and analyze its trends along the URG, with key data sourced from local hydrological and meteorological departments. Results indicated that the further back the rainfall peak was during the rainfall period, the longer the flood risk response time was, which could be shortened by increased rainfall. The time of peak occurrence of FR in the lower reaches of the river may be outside of the rainfall period: FR in these areas was lower during rainfall and starts to increase after rainfall stops, and the higher the rainfall, the more significant the increase in FR was. The RFRRP pattern remained across the URG. FR showed a decreasing and then increasing trend on the URG (Urban -- Sub-urban - Middle -- Sub-rural -- Rural). In general, FR was significantly larger in areas close to the countryside than in those close to the city, and FR in the rural area was about three times as large as that in the sub-urban area and about 1.5 times as large as that in the urban area under the 50-year return period, with differences worsening under heavier rainfall. The results of the study can guide planning and design of urban-rural integration and flood mitigation in areas with similar urban-rural gradient distribution.