*3.2. Case-Study Area*

In this study, the transposition domain selected for RainyDay is Guangdong Province in the south of China. The latitude ranges from 20.08 to 25.32 ◦N, and longitude ranges from 109.04 to 117.20 ◦E (Figure 2). The area belongs to a subtropical monsoon climate, and the rainfall has the characteristics of large amount and high intensity. The annual average rainfall is 1300 to 2500 mm. The rainfall in this area is seasonal, mainly from April to September, and record-breaking rainfall and flood disasters occur frequently during these months.

**Figure 2.** The transposition domain and the location of the case-study area (**a**), and the land use and drainage system of the case-study area (**b**).

In order to verify the rationality of the proposed framework, a highly developed and typical residential area (22.08–23.09 ◦N, 113.20–113.21 ◦E) is selected as the case-study area in Guangzhou city (Figure 2). It belongs to the subtropical monsoon climate, and the average annual rainfall is 1675 mm. Extreme rainfall events may occur throughout the year, but are mainly concentrated in April to September. In the past 60 years, the maximum and minimum annual rainfall are 2865 and 1009 mm, respectively. The area of the case-study area is about 1.55 × 10<sup>5</sup> m2, and its land use types can be generalized into three types such as building, green space, and road land (Figure 2). The slope ratio of the drainage system is 0.1~1.0%, and the pipe diameter is 600~1650 mm. The drainage system of the case-study area is designed according to rainfall accumulation at 2-yr return period. However, the regional flood problem has become increasingly prominent with increasing record-breaking extreme rainfall events.

According to the generalization theory of SWMM, the case-study area is divided into 10 sub-catchments, while the drainage system is generalized into 18 pipes, 18 manholes, and 1 outlet (Figure 2). More details are referred to in Zhu et al. [54].
