Abstract
Urban floods have been exacerbated globally, associated with increasing spatial-temporal variations in rainfall. However, compared with rainfall variabilities of intensity and duration, the effect of rainfall movement direction is always ignored. Based on 1313 rainfall scenarios with different combinations of rainfall intensity and rainfall movement direction in the typically rainy city of Shenzhen in China, we find that the effect of rainfall movement direction on the peak runoff may reach up to 20%, which will decrease to less than 5% under heavy rainfall intensity conditions. In addition, our results show that the impact of rainfall movement direction is almost symmetrical and is associated with the direction of the river. The closer rainfall movement direction is to the Linear Directional Mean of rivers, the larger is the peak runoff of section. Our results reveal that rainfall movement direction is significant to urban peak runoff in the downstream reaches, which should be considered in urban hydrological analysis.
Highlights
Extreme rainstorms have been increasing in urban areas due to continued global warming and rapid urbanization [1,2,3,4].This increase is expected to lead to an increment in urban runoff generation and, to the intensification of urban flood risks [5,6]
We found that the influence of variation in rainfall intensity (RI) and rainfall movement direction (RMD) combinations on the peak runoff can reach 30% based on the index of peak runoff deviation (Ifp) in the study area
The statistics of 538,200 Ifps show that the variations in the RI and RMD are more likely to cause negative effects on peak runoff, with 77.1% of Ifps < 1.0 and 22.9% of Ifps > 1.0
Summary
Extreme rainstorms have been increasing in urban areas due to continued global warming and rapid urbanization [1,2,3,4].This increase is expected to lead to an increment in urban runoff generation and, to the intensification of urban flood risks [5,6]. The interactions among extreme rainfall variability, river features and runoff responses remain poorly understood, especially in urban areas [11,18] Such attributions require sufficient information about the spatial distribution of short-term rainstorms and runoff responses, which is lacking in measurements for the sudden rainfall process and the complex inhomogeneity of urban areas introduced by the building envelope. While some studies have found no impact of RMD on hydrological responses [8,30], relatively few studies reported in the literature have remained inconclusive with respect to the impact of RMD on urban runoff This contrast may be explained by (1) the limited RMDs observed from rainstorm events, which is almost fixed rather than 360 degree and lacks information in an urban area; (2) isolated analyses of the impacts of RMD were conducted in these studies by neglecting the interactions between RMD and the directions of urban river segments.
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