Risk Assessment Of Fresh Water Supply Impacted By Sea Level Rise In The Shanghai Municipality

Fresh water supply plays an important role in the development of urbanization. Shanghai municipality is located in the Yangtze River estuary, as one of the largest megacity in the world. The healthy development of the society and economy in Shanghai is based on a sufficient and safe supply of fresh water resource. The water shortage caused by saltwater intrusion becomes the major risk factor of water supply in Shanghai, due to the70%of fresh water will be supplied from the reservoirs in the Yangtze estuary. The relative sea level rise in the Yangtze estuary, followed by the increase of saltwater intrusion, will intensify the conflicts between supply and demand of water resource, which will make Shanghai face the challenge of water shortage risk.The risk assessment is made by a model of fresh water supply impacted by the sea level rise in Shanghai municipality. The model includes two components as the data set of water resource utilization, and the identification of the risk factors caused by seal level rise in both water supply and demand system. The output of model consists of the medium and long term prediction of fresh water supply and demand, and water shortage risk assessment in two scenarios of population increase and two scenarios of sea level rise with the tipping point. A modified water supply guarantee rate formula is used to make the risk assessment of fresh water supply impacted by sea level rise in Shanghai municipality.The system dynamics analysis method and Vensim software are used to set up the water demand prediction SD model. It is based on large quantity of social and economic data as population, added value of industry and the tertiary industry, and statistical data of water resource utilization as domestic, industrial, agricultural, public service, etc. in the Shanghai municipality in the paper. Error check of the model output shows the model to be practical with small error. The results show that, the total fresh water demands of Shanghai in2020and2030are14.95-15.075billion m3and18.5-19.0billion m3, respectively. The domestic water demand and public service water demand will increase rapidly, and the industrial water demand will grow slowly while the agricultural water demand will be in a small decrease.The fresh water supply prediction is made by the dynamic numerical model of salt water intrusion in the Yangzte Estuary. The water supplies of Chenghang Reservoir will reduce by 0.192million m3and0.32million m3, respectively, during the dry season with the sea level rise in10cm and25cm. In the same cases, Qingcaosha Reservoir will reduce by7.55and7.77million m3and Dongfengxisha Reservoir will reduce by0.147and0.136million m3. During the extra-dry season, the water supply of Chenghang Reservoir will reduce by0.88and1.104million m3with the same sea level rise, on the other hand, Dongfengxisha Reservoir will reduce by0.216and0.264million m3.The risk assessment results about the fresh water supply shortage only by population increase show that the water shortage will occur and the guarantee rate of water supply would be lower than the safe water surplus in2021assumed to be provided by a same fresh water supply as in2012in Shanghai. And then, a big challenge of water shortage will occur in2023when the safe surplus of fresh water supply will drop to zero in Shanghai. The water supply risk may delay to2026-2027with an assumed increase of water supply in3million m3/d.Water shortage is estimated in response to two scenarios of sea level rise in5mm/a and10mm/a with the population increase. The results display the water shortage in drought season will be0.39～0.74million m3/d in2020, and8.66～9.94million m3/d in2030. It will decrease to5.66～6.94million m3/d in2030in a proposed water supply by a planned Meimaosha Reservoir. A new fresh water reservoir is proposed strongly for the water supply, regulations of fresh water utilization strategy based on the supply-decided model and the population control in Shanghai municipality are recommended in present study.