Exposure and sensitivity can be combined into potential impact,which can also be regarded as the emergy value of the potential damage and loss caused by an event.The energy system diagram of urban flooding vulnerability(Fig. 1) shows the different energy and material flows between ecological and urban economic systems, and represents the basis of cause–effect relationships among the components of vulnerability. The energy diagram consists of natural and agricultural systems and the urban system. Flows representing climatic events,economic inputs and urban responses interconnect system components. When an extreme climate event occurs, it brings rainfall overa short period of time. The amount of rainfall energy (J1) can potentially contribute to the exposure of this area to the extreme climate event. Depending on the characteristics of land cover and soil properties, a proportion of the rainfall will become runoff energy (J2),which can be regarded as the exposure of the area. J3 is the ratio of runoff (J2) to rainfall (J1), representing the intensity of exposure. The assets stored in natural and agriculture systems and the urban system can be regarded as the components of the sensitivity to vulnerability. J4 and J5 are the damages that result in the natural and agricultural systems and the urban system, respectively.The larger the stored assets the more likely flood damage will occur from an extreme climate event. J6 is the summation of total damage to both natural and agricultural systems and the urban system.The interaction of the intensity of exposure (J3) and sensitivity (J6)will represent the potential impacts (J7). Higher potential impact is likely to result in higher vulnerability. At the same time, when an extreme climate event occurs the urban system can adapt (J10)by attracting more energy from outside sources in response to the event. Finally, vulnerability is assessed by dividing the emergy of potential impacts by the emergy of adaptive capacity (J11)