Fractal tools to analyse the spatial variability of Blue Green Solutions in an urban area

A city's response to a rainfall event depends not only on the rainfall spatial-temporal variability, but also on the spatial distribution and the initial state of its Blue Green Solutions (BGS), such as green roofs. They hold back runoff and may prove being critically important elements of blue-green build environment.

The aim of this study was first to adapt the existing hydrological model to the urban area of Melun (France), to validate it and then to assess numerically an optimal configuration of green roofs to mitigate pluvial floods for particularly vulnerable areas. The main focus was put on the investigation of interactions between rainfall space-time scales and resulting hydrological response over fine scales, all being controlled by the performance assessment of BGS.

This presentation will particularly illustrate how fractal tools were used to:

- highlight the scale dependency of the input variables and its effects on gridded model performance;

- explore, analyse and represent the influence of BGS location and configuration on the mitigation of runoff associated with short-duration, high-intensity rainfall at neighborhood scale;

 - identify the urban design options that maximize the potential for runoff reduction.

In overall, these results may serve as a referential for upscaling the optimized implementation of BGS in urban areas, by considering other urban infrastructures and their interactions.