Study On The Water Change Of Poyang Lake Basin Based On System Dynamic Simulation Approach

The Poyang Lake is one of the most important freshwater resources in our country. However, the floods and droughts were becoming more and more frequent in recent years, and brought huge threaten to water safety for people that living in the Poyang Lake Basin. In order to explore the influencing mechanism of climate change and human water use on the basin flow and lake level change, the System Dynamic (SD) approach was applied to construct the water balance model of Poyang Lake basin. And the meteorological data of 8 conventional weather stations, the daily data of runoff of 5 hydrological stations (Meigang, Lijiadu, Hushan, Wanjiabu and Waizhou)and lake level monitoring data of Hukou station from 1978 to 2007 were selected to construct this model. Through singer variable control and simulations, we assumed 10% decrement and increment of precipitation, temperature and water use, and simulated the response of each link of Poyang Lake water system to these changes. This paper furtherly explored the influence path of the "precipitation-soil-runoff’ process. Finally, the water change from 2015 to 2044 was predicted under 3 different climate change scenarios. The main conclusions are as following:(1) On the whole, the system dynamic method can effectively reflect the mechanism of the basin runoff yielding and water storage process, especially applying to river and lake catchment studies. The results indicated that the SD approach can acquire an ideal performance on basin runoff yielding. The deterministic coefficient is larger than 0.88, the relative error is less than 13.8%a nd the Nash-Sutcliffe coefficient is larger than 0.68. The simulation results and the actual level of Hukou station fits well and show the change trend of water level of lake accurately.(2) Precipitation is the most critical influences on Poyang Lake basin system, while effects of the other factors are weaken during the rainy season. Effect of temperature on the basin water mainly reflected in spring and summer, the high soil moisture seasons. Of all elements related to catchment water balance process, precipitation primarily controlled surface runoff, and temperature primarily controlled evapotranspiration and soil moisture level. The effect of water use is mainly reflected in 7-9 month.(3) The correlation coefficients between precipitation and runoff was 0.958, while that between soil water storage and runoff was 0.767. The path coefficients of precipitation, soil water storage and other surplus variable on runoff correlation were 0.916、0.274 and 0.282. Seasonal change of precipitation effect on runoff is not obvious. The direct path coefficient and indirect path coefficient through soil layer showed a scale of 7:1. The influence effect of the soil layer on runoff showed a significant seasonal change, which the direct influence effect in autumn and winter was much higher than in spring and summer.(4)Based on the output of ECHAM5.0 climate patterns, under three climate scenarios of A1B, A2 and B1, the temperature of the future 30 years (2015-2044 years) shows a obviously increasing trend. And the precipitation shows growth in spring and summer, in contrast with the fall in autumn and winter. The total water production rises of 4.6%、7.3% and 3.3% respectively in the scenarios of A1B, A2 and B1. In contrast to the reduce of lake level during dry seasons, the change of water level showed increasing during the rainy seasons, which indicates that the watershed flood and drought of watershed develops toward two extremes under future climate scenarios.