Impact Factor Statistics And Analysis Of Saltwater Intrusion In The Pearl River Region

With rivers distributed in a crisscross pattern, the Pearl River Delta Region is liable to saltwater intrusion with to-and-fro water flow due to the influence of both runoff and tidal current. Since 1959, 11 severe saltwater intrusions have occurred in the Pearl River Delta Region. Since the 1990s, the saltwater intrusion in the Pearl River Delta Region has been showing the new characteristics of increasingly higher frequency, longer duration, greater upstream influence and higher severity. It has severely influenced the production and life of the local people.Based on the long-term field data, the characteristics of change in Xijiang River discharge, precipitation and average air temperature in the Xijiang River Basin are analyzed during 47 years from 1959 to 2005. By the method of departure analysis, correlativity analysis and significance test, the following conclusions are drawn.River discharge is the main factor leading to saltwater intrusion while the changes in river discharge is mainly influenced by precipitation of the region which is closely related to ENSO event; at the same time, average air temperature has weak influence on saltwater intrusion. When saltwater intrusion occurs, the river discharge and precipitation in winter and spring generally show negative departure, ONI is basically"low"or"even"and the average air temperature is slightly higher than usual.Since the 1990s, the Xijiang River discharge and precipitation in the river basin in dry season (in winter and spring) show the tendency of reducing with each passing year; and the rising tendency of average air temperature in the region is getting more significant year after year. That is just one of the reasons why the saltwater intrusion at the Pearl River mouth has been getting more frequent and severer since the 1990s.Both the precipitation and yearly fluctuation range of the Xijiang River Basin in the dry season show the decreasing tendency from southeast to northwest. The influence on the Xijiang River discharge in the dry season by precipitation of the river basin shows significant spatio-temporal difference and certain lagging. Both the influence and significance decrease with advancement to the upper stream.From November of the year prior to ENSO event to March in the year of ENSO event and from October March in the year of ENSO event to March of the next year, ONI shows significant positive correlation with the Xijiang River discharge and the precipitation in the middle and lower streams. When ONI is genitive, the probability for the Xijiang River discharge and precipitation in the middle and lower streams in post-dry season is higher than in pre-dry season. From January to March in the year of El Nino and the next year of La Nina, Xijiang River Basin shows the characteristics of drought and low river discharge. And from January to March in the year of La Nina, Xijiang River Basin mainly shows the characteristic of drought.