Development And Application Of A Forecasting Model For Extratropical Storm Surges Around The Changjiang Estuary

In China, storm surge is one of the most serious natural disasters which causes loss of life and property. The Changjiang Estuary, which is an important economic and shipping center, is attacked by not only tropical storm surges in summer but also extratropical storm surges in winter and early spring. Both kinds of storm surges threatens the economic development and the security of people living in this region. Therefore, knowledge on the extratropical storm surges around the Changjiang Estuary is of scientific and social significance.A 2D hydrodynamic model ADCIRC online coupled with a wave model (SWAN) and a weather research and forecasting model (WRF) is applied for the Yangtze Estuary and adjacent area to simulate and forecast the extratropical storm surges. ADCIRC is based on unstructured grid which can fit the complex shoreline and topography of the estuarine and coastal areas. Model nesting of ADCIRC and WRF increases both grid resolution and computational efficiency.The modeled wind speeds and water elevations were validated with observed data. And the observed data was utilized to analyse that surges happened in the high tide level, however, elevations happened in the low tide level. The model was then utilized to analyse the contribution of the wind stress and the pressure to extratropical storm surges. The results showed that the wind stress instead of the pressure is the main factor controling the extratropical storm surges. Moreover, higher river discharge increased the waterlevel during extratropical storm surges, and the waves also play an important role at the shallow depth of water.A series of numerical experiments were designed to investigate the effects of wind directions, wind speeds and wind duration of the cold wave. Under uniform wind in spatial, modeling of extratropical storm surges in 10 days or 15 days showed that onshore winds caused surges while offshore winds caused slushings. When wind directions is north by west 15°, no significant water elevations occurred. Stronger onshore wind or offshore wind increase the intensity of surges or slushings in a short period. Under constant wind directions and wind speed, surges or slushings increased severely during the first 3-4 days of the wind blowing and tended to be stable afterwards.