Flood mitigation capability assessment and classification

The maximum flood mitigation capability (FMC) of each zone is evaluated by comparing the zone’s collectable runoff volumes with the amounts of catchment runoff reduction required to maintain flood protection objectives under climate change (<em>FMC</em> = 100∀_<em>C</em> /<em>C</em>_<em>R</em><em>)</em>. The required catchment runoff volume reductions (<em>C</em>_<em>R</em>) are calculated by subtracting the amount of current flood protection capacity from the future catchment runoff volumes corresponding to each scenario and future period without GSI implementation. The collectable runoff volume (∀_<em>C</em> ) is equal to the total amount of runoff from a zone drainage area if its potential in-ground storage capacity is not reached. However, if the total runoff volume from a drainage area exceeds the storage capacity, the surplus is assumed to discharge into the primary drainage system. The results of FMC assessment are used to identify FMC classes grouping industrial SWM zones capable of mitigating the similar severity of climate change impact to below the current flood protection capacity. FMC sub-classes categorise SWM zones within each class by the key factor that limits their FMC. Sub-classes include the size of the drainage area (<em>d</em>), the high groundwater level (<em>w</em>), and the amount of potential GSI area (<em>a</em>).

通过对比各区域的可收集径流量与气候变化情境下维持防洪目标所需的流域径流削减量，可评估各区域的最大防洪减灾能力（Flood Mitigation Capability，FMC），计算公式为<em>FMC</em> = 100×∀_<em>C</em> / <em>C</em>_<em>R</em>。所需流域径流削减量（<em>C</em>_<em>R</em>）的计算方式为：在未实施GSI的前提下，以对应情景与未来时段的未来流域径流量，减去匹配当前防洪能力的径流量。可收集径流量（∀_<em>C</em>）指某区域汇水区未达到潜在地下蓄水容量时的总径流量；若汇水区总径流量超出蓄水容量，则超出部分将被假定排入主干排水系统。FMC评估结果可用于划分FMC等级，将能够将气候变化影响的相似严重程度缓解至当前防洪能力以下的工业SWM区域纳入对应等级。FMC子等级则依据限制各SWM区域FMC的关键因素，对同一等级内的SWM区域进行分类。子等级类型包括汇水区面积（<em>d</em>）、高地下水位（<em>w</em>）以及潜在GSI区域面积（<em>a</em>）。