The Response Of Peak Runoff To Rainfall Temporal And Spatial Heterogeneity In Urban Watersheds

Rapid urbanization has profoundly affected the regional hydrological cycle conditions,resulting in significant changes in the spatial and temporal distribution patterns of regional rainfall,but the spatial and temporal heterogeneity of rainfall is often simplified or ignored in the process of hydrological analysis,and the rationality of this approach is increasingly questioned.As urban communities continue to expand,urban land is being exploited,and the impervious area of urban substrates is increasing,the spatial and temporal characteristics of rainfall will become increasingly important in the hydrological process.Many scholars emphasized that the in-depth exploration of the spatial and temporal variation of regional rainfall is the key to understand the evolution of regional production and confluence patterns,and is more helpful to accurately reveal the regional runoff characteristics and mechanisms.Although a considerable amount of work has been done on the spatial and temporal variability of rainfall and runoff characteristics under urbanization,"how to cope with the problem of lack of rainfall data with high spatial and temporal resolution in urban areas for rainfall frequency analysis? However,"How to characterize the variability of rainfall in urban areas in temporal and spatial dimensions?" And,"How is the peak runoff affected by the spatial and temporal heterogeneity characteristics of rainfall?" These scientific questions are still not well answered and thoroughly investigated.Therefore,to address this series of scientific problems,this study will carry out the following:(1)Based on a storm generator model called "Rainy Day" using stochastic transposition technique(SST),coupled with short time series(2008-2016)raster rainfall data,to solve the current problem of lack of long time series rainfall monitoring data in urban areas,and improve the accuracy of rainfall spatial and temporal resolution in rainfall frequency analysis.(2)Based on the(1)we obtain the design rainfall scenarios with different rainfall durtion and spatial and temporal distribution,and then construct a rainfall spatial and temporal heterogeneity index system to explore the variation of regional rainfall in temporal and spatial dimensions.(3)We constructed three different urban development subsurface scenarios,and simulated the urban sink processes through the GSSHA two-dimensional distributed hydrological model to analyzed the variation rule of peak runoff in three different urban development subsurface scenarios.Also we use the covariance analysis method and the constructed rainfall spatial and temporal heterogeneity index system to quantitatively reveal the influence of different rainfall spatial and temporal heterogeneity indexes on the peak runoff under different urban development subsurface scenarios.Through the analysis of the above,the following conclusions can be obtained:Based on the short time series(2008-2016)raster rainfall data,the "Rainy Day" rainfall generator model can create the design rainfall which the rainfall spatial and temporal distribution are similar to the actual rainfall,and the design rainfall with specific spatio-temporal distribution characteristics can be obtained.In the reconstructed rainfall scenarios,even with the same rainfall amount,there are obvious differences in time and space.In aspect of the temporal distribution of rainfall,the temporal distribution of rainfall in different rainfall scenarios shows obvious differences that the rainfall peak can be occurrd earlier,middle or later.What's more,there are also obvious differences in the concentration of rainfall in different rainfall scenarios.From the spatial distribution of rainfall,there are also significant differences in the total amount of rainfall in each raster and its rainfall volume at each moment.The spatial and temporal heterogeneity of rainfall has a significant effect on the peak runoff.That is,the spatial and temporal heterogeneity of rainfall has a stronger effect on peak runoff than the effect of rainfall duration and rainfall volume.Coupled with the change in the impermeability of the urban subsurface,the spatio-temporal heterogeneity of rainfall has a stronger effect on the peak runoff,i.e.,as the impermeability of the subsurface increases,more rainfall scenarios with small rainfall return periods or short rainfall durations produce a higher peak runoff than those with large rainfall return periods or long rainfall durations.The contribution of rainfall spatial and temporal heterogeneity index indicators to the peak runoff in different urban open impervious subsurface scenarios has a significant variation.Overall,the rainfall peak coefficient(r)and rainfall concentration(PCI)contribution are the best to the peak runoff.The contribution of r to peak runoff can reach up to more than 50%,while the contribution of PCI to peak runoff can reach up to more than80%.And the contribution of the 1-h maximum rainfall to the peak runoff shows a pattern of decreasing with increasing time,and the overall contribution ranges from 10% to 40%.And under the same rainfall duration,with the increase of imperviousness of the underlying surface,the influence of the r on the peak runoff in each rainfall return period shows a regular change of decreasing and then increasing,but the opposite situation occurs for the PCI.And the effect of 1h maximum rainfall on the peak runoff is greatest under the underlying surface with the imperviousness of 100% in the short rainfall return period.Although the contribution of the total rainfall center and 25mm/h rainfall coverage index on the peak runoff are smaller,both of them have certain non-negligible influence on the peak runoff.It is worth mentioning that the interaction between the indicators in different subsurface scenarios has a greater influence in each return period and rainfall duration,i.e.,the influence of the interaction between the elements on the peak runoff cannot be neglected.