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The topography is low and flat in the estuarine region of the Yangtze River, where waterlog and salt-affected soil are all through a latent threat to the agricultural development for long time. After the Three-Gorge Project is built up, the Three-Gorge Reservoir adjusts seasonably runoff will impact on the dynamic of soil water and salt in the region. These influence relations are very complicated. Based on the theory of solute transport and the principle of soil water dynamics, the model of soil water and salt transport was created, which involved root water extraction, adsorption-desorption, mobile-immobile region. To overcome numerical dispersion, the paper solved the convection-dispersion equation by Bresler algorithm, the term of time derivative used the approximate difference formula of quadratic differential coefficient based on central difference. Then, the impact of Three-Gorge Project on the regime of soil water and salt in the estuarine region by numerical simulation was studied in. The numerical simulation indicates that electric conductivity of soil one meter thick of each observed section will go down by 0.005-0.174 mS/cm as discharge increases in spring after building the Three-Gorge Reservoir, and up by 0.004-0.416 mS/cm as discharge decreases in autumn-winter. The elementary predicted result of numerical simulation shows that salification will be bigger in autumn than desalinization in spring. The impact degree of the project on the regime of soil salt will be gradually weakened along the river up from the estuary, the nearer to the sea, the bigger the impact, and from cross profiles, the nearer to the river, the bigger the impact. Especially within the range of 4 km of the river, it is more possible that the soil will produce salification or secondary salinization. [ABSTRACT FROM AUTHOR]

Middle and eastern routes of the South-North Water Diversion Project (SNWDP) of China, which are approximately located within the area 28°-42°N and 110°-122°E, are being constructed. This paper investigates the past climatic variations on various time scales using instrumental and proxy data. It is found that annual mean surface air temperature has increased significantly during the past 50-100 years, and winter and spring temperatures in the northern part of the region have undergone the most significant changes. A much more significant increase occurs for annual mean minimum temperature and extreme low temperature than for annual mean maximum temperature and extreme high temperature. No significant trend in annual precipitation is found for the region as a whole for the last 50 and 100 years, although obvious decadal and spatial variation is detectable. A seesaw pattern of annual and summer precipitation variability between the north and the south of the region is evident. Over the last 100 years, the Haihe River basin has witnessed a significant negative trend of annual precipitation, but no similar trend is detected for the Yangtze and Huaihe River basins. Pan evaporation has significantly decreased since the mid-1960s in the region in spite of the fact that the trend appears to have ended in the early 1990s. The negative trend of pan evaporation is very significant in the plain area between the Yangtze and Yellow Rivers. There was a notable series of dry intervals lasting decades in the north of the region. The northern drought of the past 30 years is not the most severe in view of the past 500 years; however, the southern drought during the period from the 1960s to the 1980s may have been unprecedented. The dryness-wetness index (DWI) shows significant oscillations with periodicities of 9.5 and 20 years in the south and 10.5 and 25 years in the north. Longer periodicities in the DWI series include 160-170- and 70-80-yr oscillations in the north, and 100-150-yr oscillations in the south. The observed climate change could have implications for the construction and management of the SNWDP. The official approval and start of the hydro project was catalyzed by the severe multiyear drought of 1997-2003 in the north, and the operation and management of the project in the future will also be influenced by climate change-in particular by precipitation variability. This paper provides a preliminary discussion of the potential implications of observed climate change for the SNWDP. [ABSTRACT FROM AUTHOR]