Lessons learnt from Typhoons Fitow and In-Fa: implications for improving urban flood resilience in Asian Coastal Cities

Frequent typhoons significantly affect many coastal cities via intensive rainstorms, tidal surges and strong wind. Natural factors induced by human disturbance such as climate change and sea-level rise come alongside anthropogenic factors such as rapid urbanisation and land use/land cover change, leading to detrimental consequences such as urban floods. This short communication offers various lessons learnt by Ningbo municipality from two strong typhoons that hit the city directly, namely Fitow in 2013 and In-Fa in 2021. On the one hand, usage of “Big Data” and “Social Media” for better “Preparation” and “Prevention” reduced flood impacts noticeably. On the other hand, implementation of “Flood Insurance” sped up the “Recovery” processes. The successful “Preparation”, “Response” and “Recovery” helped Ningbo to enhance its flood resilience, and thus to reduce or avoid substantial impacts of injuries, household damages and the associated economic loss. These three key terms should be heeded in typhoon/flood governance in which various stakeholders are involved, and be incorporated into the city’s long-term strategic development plans to merge with the climate actions towards the 2030s and beyond. This will be vitally important in reducing climatic hazards and improving coastal flood resilience under the future climatic uncertainties in Asian coastal cities.


More upcoming typhoons and extreme storms
The coastal regions in East Asia, such as the East and South coast of Chinese provinces including Zhejiang, Fujian and Guangdong, are experiencing particularly frequent typhoon disturbance and facing great flood risk due to rapid urbanisation and extensive development on the low-lying coastal plain with little topographic relief and thus are prone to floods (Wang 2018). For example, the prospect of climate change will likely exacerbate the temperature increase of seawater and increase the magnitude of low-pressure systems associated with tropical cyclones in the West Pacific in the upcoming future (Griffiths et al. 2019). This will impact the deltaic region of the Yangtze River and the Pearl River, two most important economic centres and logistic hubs in southeast China, where many major cities like Ningbo, Shanghai, Hong Kong, Shenzhen and Guangzhou are located . The Hong Kong Observatory (Hong Kong Special Administrative Region' Meteorological Office) recorded over 40 typhoon visits in the Pearl River Delta in the 1990s and 2000s, and expected typhoons, storm surges and intensive rainstorms will visit the region more often in ensuing decades (Woo and Wong 2010).
Obviously, the probability of urban surface floods in coastal cities in southeast China is increasing due to the following factors: (1) more frequent and intensive rainstorms that exceed the capacity of the current land drainage system ); (2) surge-enhanced backlash of seawater that might affect land drainage systems; (3) direct inundation by extreme tidal changes via storm surge ) and (4) the coactive impacts of these factors. In addition, global sea-level is predicted to rise by 0.2 to 0.4 m over the next 50 years (Hallegatte et al. 2013), which would be as much as 1.2 to 1.8 m by 2100 under various economic development scenarios and climate change models (Church and White 2011;Verheggen et al. 2014;Nerem et al. 2018). Locally, the Hong Kong Observatory and the China's State Ocean Bureau estimated an annual sea-level rise rate at 2.1-2.3 mm/ year from the 1950s up to now, which means we can expect about 0.6 to 0.7 m increase if nothing changes substantially ). These dual effects would bring further challenges to flood governance.
This short communication aims to illustrate how Ningbo managed to minimise injuries and damages in two Typhoon events, namely "Fitow" in 2013 and "In-Fa" in 2021, and meanwhile to enhance the city's climate resilience by integrating Climate Action Plans (focussing on Preparation, Prevention and Recovery) with long-term strategic development plans. The successful experiences of Ningbo should be heeded in typhoon/flood governance of many other Asian coastal cities prone to flooding.

Ningbo-background
Ningbo is a typical coastal city located in the east coast of China ( Fig. 1), with immense annual rainfall (50% of the mean annual rainfall at about 1500 mm) during typhoon season that runs from June to October annually. By contrast, rainfall in dry season (November to February) normally ranges from 250 to 300 mm annually. Water resources management in Ningbo focuses on not only the capacity of dams and reservoirs to prevent the outburst of dams under storms, but also the provision of adequate water resources during dry season (Griffiths et al. 2017). The majority of the city's 9816 km 2 land area is flat, with elevation ranging from 2 to 10 m above-sea-level, whereas the tidal range is from 1.6 to 5.8 m.
Traditionally, Ningbo is equipped with a land drainage system that can only handle rainfall events at 1-in-1 to 1-in-5 years return period. This means the city is at high risk during the typhoon period, as intensive stormwater is difficult to be discharged quickly through the drainage system and three tidal rivers (Yao River, Fenghua River, and Yong River), particularly when the surges are concurrently raising the river level to decrease the runoff capacities ). Since 1950s, fifty typhoons have hit Ningbo, caused 12 severe floods, and resulted in economic losses totalling an estimated RMB93 billion (Tang et al. 2015). Taken together, surges and astronomical tidal inundation in typhoons and storms period present challenges and risks to the city. Since 2015, the city joined the nation-led Sponge City Programme (SCP) as one of the pilot cities, with an aim to raise stormwater protection capacity to handle storms at 1-in-30 years return period. Through retrofitting urban drainage system that aiming and constructing integral green-blue infrastructure in 80% of its urbanised area by the end of 2030s Tang et al. 2018;Qi et al. 2020;).

Typhoon Fitow and In-Fa
Typhoon "Fitow" made landfall on the 7th October 2013 in Fuding (northern Fujian Province) that is located at the boundary between Fujian and Zhejiang Province, and influenced Ningbo severely. It affected over three million people in Zhejiang and produced prolonged intensive rainfalls and storm surges that were aligned with a second typhoon (Danas) right after Fitow. A rainfall of 263 mm/24 h was recorded in the main urban districts of Ningbo including Yuyao, Fenghua, Yinzhou, Haizhu districts (Griffiths et al. 2019). Particularly, more than 100,000 properties in Yuyao district were inundated, and the economic loss was estimated at about RMB2 billion (at 2013 rate). The intensive rainfalls could not be discharged via the city's land drainage and the canal/river network because of the high level of river flow attributed to the high tide levels (Tang et al. 2015). Stormwater overtopped canal walls and caused severe pluvial floods (see Fig. 2). Typhoon "In-Fa" (literally it means fireworks), the sixth tropical storm of this year, landed in Zhoushan (right besides Ningbo on the east coast of Zhejiang) at 12:30 pm on  (Li, 2021a). The typhoon, after making landfall in Zhoushan, moved through Hangzhou Bay and made a second landfall at Pinghu located between Hangzhou and Shanghai at 0950 am on 26 July 2021, with the maximum wind speed at 100 km/h (Ma 2021). "In-fa" initiated from the West Pacific close to Guam on 16 July 2021 (9 days before making landfall in China's coastal area). This typhoon started with an average speed of 25mph to 70mph during 16-20 July, and was recognised as a category 1 typhoon (74-85 mph) on 20 July 1300 and then category 2 (at 96-110 mph) during 21 July 0700 am and 22 July 1900 pm (Weather Underground., 2021). Indeed, the wind of In-fa was not a concern, but rather the large coverage of lowpressure and enhanced intensive rainstorms that mattered. Between 24 and 27 July, intensive rainstorms brought heavy downpours at 150-200 mm/24 h in Ningbo. Particularly, Yuyao and Haizhu districts recorded 539 mm/72 h and 454 mm/72 h rainfalls, respectively. A monitoring station at Yuyao district recorded a historical accumulated rainfall of 1003 mm from 19 to 22 July (Tencent News 2021). All other districts, such as Yinzhou, Fenghua, Xiangshan, recorded over 400 mm/72 h rainfalls. In-Fa caused severe surface water flooding and rapidly increased urban water level of river networks in the catchment area of Ningbo (Wang 2018).

Good "Preparation"
Typhoon In-Fa has brought torrential downpours to Ningbo and the region across Zhejiang and a few neighbourhood provinces. Particularly, Ningbo was facing coactive effects of "rainfalls", "tides" and "wind" according to the China Meteorological Administration (PHYS 2021). The municipal government was well prepared, through identifying high-risk areas (such as hilly and low-lying flood prone zones) and issuance warnings periodically. Major airports and transport hubs were shut down and public were persuaded to stay at safe places (Chen 2021a). Moreover, timely relocation service was executed to evacuate communities from "high risk" areas to temporary shelters (such as sports halls, schools and community service centres, etc.), where basic essentials were provided, including cup noodles, hot water, bathing places, toilet, air conditions and even televisions. Affected residents can stay at these places free-of-charge until the event was completely over (Hu 2021). During In-Fa, more than 421,000 residents were relocated before severe impacts occurred. This is key to ensuring "zero casualties" in this fierce typhoon event.

Smart technologies helped to build effective "Response"
The importance of social media and technologies such as "Big Data" and "Smart Technologies" has been recognised by the municipal government to disseminate warnings through a joint public-private partnership and ensures effective public-private communication before, during and after the typhoon event (Zhou 2021). Ningbo municipal government worked closely with mobile companies to collect and analyse big data, disseminate information effectively through artificial intelligence, and 5G e-platform. Particularly, social media can update users with real-time information such as disruptions of services caused by flooding (e.g. disrupted roads) and high-risk areas. Social media also helped accelerating the responses from the emergency services (e.g. police, fire services, army, ambulances and medical services) (BendiBao 2021). 3D mapping services helped the governmental agencies to identify inundated communities (e.g. Dongqiao town), specify safe rescue routes for providing essential services (e.g. water, food, etc.) (Tieshou 2021). Social media users also volunteered to urge the public to prepare power bank in case of power outage during the typhoon and flooding period, as understood the importance of mobile phones and smart technologies in receiving information and seeking assistance when needed (Ningbo Minsheng e-point 2021). We have yet to finalise an assessment of social media in this event. Nevertheless, according to Weibo (an e-platform) data, we have found there are over 2.45 billion times discussions about this typhoon event regarding awareness, preparation and governmental responses, which demonstrated the vital importance of social media in building resilience and minimising damages.

Supportive, helpful and caring "Recovery"
A key lesson learnt from typhoon Fitow in October 2013 was how to reduce economic loss, which was estimated to be as high as 33 billion RMB (Sina News 2021), which stressed the need to establish a systematic and adequate flood insurance programme, an essential practice to reduce households' financial risks associated with their properties and assets. An encouraging news is that in association with Typhoon In-Fa event, the insurers (such as insurance companies, re-insurance companies and banks) are improving their services through e-platform and smart technologies (Li 2021b). For example, relying online document submission and scrutiny, the handling processes were speed up and insured clients can get financial compensation within 20 min (Chen 2021b).
Additionally, municipal government worked very hard to ensure affected communities getting adequate supports via a supportive, helpful, caring and speedy recovery processes, such as public infrastructure improvement (sorting out road damages, retain public transport), adequate food supply, water and sanitation services (Dominique and Sophie 2021). Also with enhancement of public perception, participation and post-disaster' education (via schools, universities and communities), so that residents could recover from typhoon and resume their normal life effectively.

Concluding remarks-moving towards "Coastal Resilient Cities"
Practices focussing on preparation, prevention and recovery ensured "zero causalities" and a significant reduction in economic loss of the In-Fa event, for example, Ningbo's Cixi district suffered a RMB2.03 billion loss at Fitow, but only RMB 0.19 billion from In-Fa (Wen 2021). The success of Ningbo municipal government and all stakeholders are truly champions. The lessons learnt from Fitow and successful experience of In-Fa in Ningbo city could be heeded in typhoon/flood governance of other Chinese and Asian coastal cities. Urban resilience can be improved by integrating flood "Preparation", emergency "Responses" and post-disaster "Recovery" into a city's long-term development plans, such as "Master Plan" and "Climate Action Plan". Particularly, these practices should also be merged with the nation's "Sponge City" Programme, which prioritises grey-blue-green infrastructure but obviously lacks the social dimension, which is urgently needed in the light of hectic "Sponge City" construction and climatic uncertainties.