# **Summary of results**

This paper describes the methodology and findings for the extreme hazard exposure analysis of the Chinese wastewater sector to flooding and earthquakes hazards. This analysis is undertaken for changing flooding, under climate scenarios, and earthquake exposure of a spatially accurate wastewater treatment plants (WWTP) database for China, covering a total of 1,346 assets with additional attributes quantifying the treatment capacity and users dependent on each plant.

For flooding, we apply a global river routing (CaMa‐Flood) model that quantifies the change degree of flood exposures from the present time‐period (1980‐2005) to the near future time‐period (2016‐2035) to a far future time period (2036‐2055). These changes are evaluated for all floods exceeding 1 in 30, 1 in 50 and 1 in 100 events as estimated through an ensemble of 11 climate models under RCP4.5 and RCP8.5 climate scenarios.

For earthquakes, we use Peak Ground Acceleration (PGA) hazard maps for return periods of 250‐, 475‐, 950‐, 1500‐, and 2475‐years, and group PGA into five discrete categories: Very High **VH** (>0.65g), High **H** (0.34g ‐ 0.65g), Medium **M** (0.18g ‐ 0.34g), Low **L** (0.092g – 0.18g), and Very Low **VL** (<0.092g). Similar categories are assumed for liquefaction susceptibility: VH, H, M, L, VL. These are based on a readily available dataset created for use at the global scale using a calibrated geospatial prediction model.

# **_Flood exposure results_**

Our analysis shows that more numbers and users of WWTPs will witness an increase in extreme flooding exposures, in comparison to the numbers of WWTPs that will witness a decrease.

- Under RCP4.5 emission scenarios, 10 out of 11 climate models are in complete agreement of a net increase in plant exposure numbers and users impacts for all flood exceedance probabilities in the near future. In the far future, all 11 models agree that there will be a net increase in plant exposures and user impacts for all 1 in 50 and 1 in 100 flood exceedance probability events.

- Under RCP8.5 emission scenarios, 9 out of 11 climate models are in complete agreement of a net increase in plant exposure numbers and user impacts for all flood exceedance probabilities in the near future. In the far future, all 11 models agree that there will be a net increase in plant exposures and user numbers for all 1 in 100 flood exceedance probability events.

- The net user impacts of increasing flooding exposures for events exceeding 1 in 30 return periods can be as high as approximately 180 million in the near future under RCP 4.5 emission scenarios, which potentially grows to about 208 million in the far future. The averages of net users facing increasing exposures increases from 47 to 61 million between the near and far futures.

- The changes under RCP 8.5 are similarly severe with about 121 million net users impacts from increasing WWTPs flooding for events exceeding 1 in 30 return periods in the near future, which potentially grows to about 187 million in the far future. The averages of net users facing increasing exposures increases from 40 to 72 million between the near and far futures.

- Spatially we observe that in the near future, flood hazards for RCP 4.5 are concentrated along the Yangtze River, in southern Hubei, northern Hunan, central Anhui, northern

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