# **1. Introduction**

Wastewater infrastructure has seen phenomenal growth across China in recent decades (Zhang _et al._ , 2016; Mumbengegwi, Li and Muhoza, 2018). From 1991 to 2003, treatment capacities have increased from 400 to 3800 ML (megalitres) and treatment efficiencies from 14.9% to 89.3% (Zhang _et al._ , 2016). Much of this infrastructure was built for the purposes of sanitation, environmental health, and to serve the need to reuse water due to pressures of growing water demand from rapid urbanization.

Typically, wastewater infrastructure systems span city‐scales with large collecting catchments conveying water to centralized wastewater treatment plants (WWTPs), and finally a disposal to the environment (Libralato, Ghirardini and Avezzù, 2012). While centralized treatment plants tend to be more cost effective, they are highly reliant on single assets (i.e. the plants themselves) which means that there is great potential for widespread services losses or significant reductions treatment capacity should they become partly or completely inoperable.

Natural disasters have been known to cause problems in wastewater service provision. Significant rainfall for example, may see increased rates of inflow and infiltration often leading to system overflows of raw wastewater to the receiving environments whether it is land or a receiving stormwater/river system. Similarly, WWTPs are often at greater direct risk to fluvial and coastal flooding given the tendency to locate the assets in lower lying areas or near rivers and coasts to take advantage of gravity conveyance and for proximity to a disposal water body. On the other hand, earthquakes and related ground deformation may cause disruptions to the system through pipe breakages, mechanical equipment failures, and structural failures of tanks and related storage equipment.

In recent decades, no country other than China has experienced more frequent major damaging natural hazard events, with only the exception of the USA suffering higher economic losses (CRED and UNISDR, 2018). The majority of these expected annual damages in China can be attributed to flooding and earthquakes (CRED and EM‐DAT, 2019). Some recent globally significant flooding and earthquake events include the 2016 Yangzte and Huai River Flooding and the 2008 Sichuan Earthquake, both of which resulted in widespread losses of life and property, and infrastructure damage. With climate change, the frequency and severity of climate related flooding hazards are expected to rise, thus posing an ever increasing threat to China’s wastewater infrastructure networks – in particular WWTPs given their proximity to water bodies for treated effluent discharge.

In contrast, while the risk of earthquakes is not necessarily increasing (Shearer and Stark, 2012) compared to climatic hazards, the potential damages from shaking, ground deformation, and secondary hazards are particularly relevant for China given its vast size, proximity to fault lines, and large river systems. Secondary hazards from earthquakes are also of concern, such as the increased flood risk arising from landslide dams in upstream catchments, ground subsidence in coastal areas, and where liquefaction, lateral spreading, and sedimentation leads to bed rises and narrowing of river channels and flood plain.

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