Sustainable Measures for Mitigation of Flooding Hazards: a Case Study in Shanghai, China
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water Article Sustainable Measures for Mitigation of Flooding Hazards: A Case Study in Shanghai, China Yao Yuan 1,2, Ye-Shuang Xu 1,2,* and Arul Arulrajah 3 1 State Key Laboratory of Ocean Engineering, School of Naval Architecture, Ocean, and Civil Engineering, Shanghai Jiao Tong University, Shanghai 200240, China; [email protected] 2 Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration (CISSE), Shanghai Jiao Tong University, Shanghai 200240, China 3 Department of Civil and Construction Engineering, Swinburne University of Technology, Melbourne, VIC 3122, Australia; [email protected] * Correspondance: [email protected]; Tel.: +86-21-3420-4301 Academic Editors: Franco Salerno and Athanasios Loukas Received: 23 February 2017; Accepted: 25 April 2017; Published: 28 April 2017 Abstract: Global warming induces temperature variations and sea level changes for a long period of time. Many coastal cities around the world have experienced the harmful consequences of sea level changes and temperature variations. The city of Shanghai in China also suffers from the serious consequences of these two climatic factors. The geological and climatic conditions of Shanghai make it sensitive to flooding risks during heavy rainfall events. This paper analyses the conditions of sea level changes, temperature variations, and heavy rainfall events in Shanghai. Correspondingly, eustatic sea level change, tectonic movement of the continent, and land subsidence in Shanghai have effects on sea level changes. Correlation analysis indicates extraordinary short duration rainfall events have a relationship with temperature variations due to global warming. Moreover, the number of extraordinary torrential rainfall events also has a correlation with sea level changes. Pluvial flooding and potential damage to coastal structures are more likely to have serious effects as the number of flooding hazard events due to global warming and sea level changes increases. This study also established that to efficiently protect the environment, control economic losses, and prevent potential hazards, extra countermeasures including monitoring, forecasting, and engineering technology treatment should be adopted. Monitoring measurements combined with a database system on a website was found to be useful for forecasting and simulating flooding hazards. For systematic sustainable urban water system management, appropriate treatment technologies, such as sustainable urban water system, which can control and manage water quantity and quality, namely “the Sponge City”, should also be considered. Keywords: global warming; sea level variations; torrential rainfalls; flooding hazards; Shanghai 1. Introduction In recent decades, global warming, which is a mix of rising temperatures and unstable climate, has been an important issue in the research of environmental changes. Research indicates that the presence of greenhouse gases in the atmosphere and human activities are the main contributing factors that cause global warming [1,2]. Numerous coastal mega-cities around the world have experienced hazards due to global warming. These hazards include increased demand for groundwater due to temperature rise [3–6], ocean acidification, and the collapse of ecosystems worldwide on land and at sea [7–10]. Moreover, rising temperatures and rising sea levels due to global warming tend to increase the probability of heavy rainfall risks, particularly in coastal cities [11,12]. The increase in the number of intensive precipitation events will also increase the potential risks for pluvial flooding resulting in Water 2017, 9, 310; doi:10.3390/w9050310 www.mdpi.com/journal/water Water 2017, 9, 310 2 of 16 the endangerment of urban safety. China has a coast line that extends over a distance of 18 thousand kilometers. Sustainable economic and social development of many coastal cities in China has been endangeredWater 2017 by, the9, 310 adverse effects of global warming that include typhoons and pluvial flooding.2 of 16 Shanghai is located on the south bank of the Yangtze River, bordered to the east by the East China Sea,kilometers. and is Sustainable one of the economic largest coastal and social cities development in the world, of many occupying coastal cities an area in China of 6340 has kmbeen2 [13,14]. The geologicalendangered profile by the of adverse this city effects is mostly of global composed warming that of include soft deltaic typhoons deposit and pluvial [15–18 flooding.]. The Huangpu Shanghai is located on the south bank of the Yangtze River, bordered to the east by the East River, a tributary of the Yangtze River, runs through Shanghai. Figure1 presents a schematic of the China Sea, and is one of the largest coastal cities in the world, occupying an area of 6340 km2 [13,14]. ShanghaiThe administrative geological profile region of this [ 19city–23 is ].mostly The annualcomposed rainfall of soft isdeltaic approximately deposit [15–18]. 1200 The mm, Huangpu of which 60% falls duringRiver, the a tributary flooding of season the Yangtze from River, May runs to September through Shanghai. [24–27]. Figure The first1 presents month a ofschematic the flooding of the season (the monthShanghai of May) administrative is usually region referred [19–23]. to as The the annual ‘Meiyu rainfall period’, is approximately in which rainfall 1200 mm, events of which last 60% for several days. Sincefalls during the 1980s, the flooding Shanghai season has from constructed May to September numerous [24–27]. drainage The first systems, month suchof the as flooding water sluices and drainageseason pumps;(the month however, of May) is high usually precipitation referred to stillas the leads ‘Meiyu to pluvialperiod’, in flooding which rainfall events, events which last result in for several days. Since the 1980s, Shanghai has constructed numerous drainage systems, such as huge economicwater sluices losses, and drainage and furthermore pumps; however, endanger high precipitation urban safety. still Global leads to warming pluvial flooding brings events, about more extremewhich storms, result such in huge as typhoons, economic losses, which and frequently furthermore increase endanger the urban flood safety. hazard Global level. warming For example, Typhoonbrings Canhong about more in 2015, extreme which storms, landed such in as Zhejiang typhoons,province, which frequently resulted increase in economic the flood losses hazard totaling 1.98 billionlevel. RMB For example, (about 300Typhoon million Canhong $USD) in [ 282015,]. Rainfall-runoff which landed in due Zhejiang to typhoons province, caused resulted more in than ten thousandeconomic buildings losses totaling to be inundated.1.98 billion RMB Thus, (about it is necessary 300 million to $USD) analyze [28]. the Rainfall-runoff effects of global due to warming typhoons caused more than ten thousand buildings to be inundated. Thus, it is necessary to analyze with respect to flooding risks and to propose appropriate countermeasures to cope with the impact of the effects of global warming with respect to flooding risks and to propose appropriate global warming.countermeasures to cope with the impact of global warming. Jiangsu N Chongming Yangtze Island River 0 10 20km Jiading Changxing Island Baoshan Jiangsu Urban area Huanpu Park Pudong New Suzhou river Development Qingpu Xu jiahui Songjiang Minhang Nanhui East Huangpu River China Fengxian Sea Zhejiang Jinshan Hangzhou Bay Meteorological station Figure 1. Schematic view of Shanghai depicting the locations of the meteorological stations. Figure 1. Schematic view of Shanghai depicting the locations of the meteorological stations. At present, Shanghai’s elevation ranges from 2.2 to 4.5 m above the mean sea level [29], with Atsome present, central Shanghai’s parts of the elevationurban area rangesbeing lower from than 2.2 3 m to [29,30]. 4.5 m aboveBased on the the mean China seaOcean level Bulletin [29], [31], with some central partsthe eustatic of the sea urban level areain Shanghai being has lower increased than 3by m 115 [29 mm,30]. over Based the onpast the thirty China years. Ocean In addition, Bulletin [31], continental tectonic movement and human activities such as groundwater withdrawal [32–35], pipe the eustatic sea level in Shanghai has increased by 115 mm over the past thirty years. In addition, jacking constructions [36–38], deep excavations [39–42] and tunnel constructions [43,44] tend to continentalinduce tectonic the land movement subsidence and have human an effect activities on the suchrelative as sea groundwater level. Due to withdrawalthe low elevation [32 –of35 ], pipe jackingShanghai, constructions pluvial [36 flooding–38], deep events excavations are more likely [39 –to42 occur] and with tunnel relative constructions sea level rises. [43 It,44 is ]therefore tend to induce the landincreasingly subsidence urgent and haveto provide an effect appropriate on the relativecountermeasures sea level. to Duecontrol to relative the low sea elevation level changes of Shanghai, pluvial floodinginduced by events global arewarming. more likely to occur with relative sea level rises. It is therefore increasingly urgent to provideThe objectives appropriate of this paper countermeasures are to: (i) discuss tothe controlcorrelation relative between sea heavy level rainfall changes events induced and by associated factors, namely, sea level changes and temperature variations induced by global warming; global warming. The objectives of this paper are to: (i) discuss the correlation between heavy