Changes of Precipitable Water Vapor in Three Gorges Region by ground based GPS and numerical simulation

After the first impoundment of the Three Gorges Reservoir in the first ten days of June 2003, the acreage covered by water increased. As the increased water cover over land during the initial impoundment period, the atmospheric dynamical conditions and water vapor transportations in the local area could be changed. Aim to see whether water vapor changes and its magnitude, detailed observations of Precipitable Water Vapor (PWV) from the Crustal Movement Observation Network of China and the Yangtze River Three Gorges Global Positioning System (GPS) Network are analyzed as well as numerical sensitive experiments. The PWV data were retrieved from electromagnetic signal phase delays measured by the Ground-based GPS sites in the target and reference networks. The retrieved PWV datasets were compared to Radiosonde (RS) observations and shows good agreement. It is indicated that the retrieval methods are physically reasonable. Using the ground based GPS observations (per 30min one data) during 2000-2004 in Three Gorges Region (TGR), PWV is retrieved by the Bernese optimize software and the localized retrieval method with the mean deviation of 3.3mm and the correlation coefficient of 0.94. After the first impoundment in 2003, the PWV time series of 2 sites in TGR show that the annual variation of PWV peak value is 3-5 mm higher than before. Monthly variation shows the abnormal in the first winter and spring. The diurnal variation shows the mean PWV is 6mm higher than several days before. Based on the WRF model, control and sensitivity simulation experiments are used to discover the water vapor change in TGR influenced by the reservoir impoundment. It is shown that rainfall, water vapor, and humidity obviously are increased with the increasing of the water surface in TRG, and these physical quantities in lower layer are more sensitive to the surface types changing in summer and winter.