Rapid quantification method and parameter sensitivity analysis of waterlogging water surface ratio in urbanized areas: A case study of Guangzhou downtown area
As the urban waterlogging issue grows increasingly prominent, rapid quantification of the water surface ratio of waterlogging has become an integral part of improving the efficiency of urban stormwater management. Based on the water balance equation and the theory of stormwater volume calculation, this study derives an analytical formula that links the water surface ratio of waterlogging to the key parameters of rainfall intensity, land area composite runoff coefficient, catchment concentration time, and storage depth. By substituting the proposed closed-form solution for the conventional iterative algorithm, the water surface ratio of waterlogging can be quantified rapidly and explicitly. Taking the central urban area of Guangzhou as a case study, this paper systematically evaluates how the water surface ratio of waterlogging responds to variations in the study area, storage depths, rainfall durations, and rainfall return periods. The results show that the water surface ratio of waterlogging is positively correlated with the rainstorm intensity, land area composite runoff coefficient, and catchment concentration time; but negatively correlated with the storage water depth. The water surface ratio of waterlogging increases with the increase of the rainfall return period and rainfall duration, while decreases with the increase of the study area. When the storage depth is less than 0.7 m, the water surface ratio of waterlogging decreases significantly with the increase of storage depth. Sobol global sensitivity analysis further indicates that the storage depth is the dominant parameter, followed by the rainfall return period; whereas the study area and rainfall duration exhibit only minor influences. This method provides an expeditious accounting program to quantify water surface ratio of waterlogging for urban flood control and sponge city planning.