Analyzing The Rainfall Change For 50 Years And Its Affect On The Vulnerability Of Karst Aquifer In Chongqing

With the rapid growth of science and technology in the 20th century, people were trying to remodel the nature as the result their survival environment was gradually destroyed.Especially in the last 30 years of the 20th century, global warming and the extreme weather events were increasing continuously. So the climate change and the impact of human activities became one of the important objects of the research. In China, natural disasters happened frequently and the ecosystem was destroyed seriously this year. Chongqing, in the upper reaches of the Yangtze River, east of the southwest of China, it’s annual accumulated temperature rised gradually, warm winter phenomenon was particularly serious in this year, the droughts and the heavy rain happened at intervals and frequently, as a result the fluctuation of grain production reduced, and caused the economic loss and a huge threat to people’s lives and property.At least 2 billion people worldwide use groundwater as their drinking water. However with the development of economic, industrial and the level of urbanization, more and more pollutants were discharged into the underground water, and caused a great threat to the life and production. Especially in karst area, the lack of natural impervious layer and filter layer, pollutants and surface water go into the aquifer and underground river easily, so as a fragile environment, it is very important to assess the vulnerability of the karst area.At the same time the vulnerability will vary with the climate and land use change. The more recharge, the more probability of the pollution in groundwater. So the rainfall is the main source of the groundwater recharge. The rainfall, the rainfall frequency, the duration of rainfall and the extreme rainfall times will affect the migration time of the pollutions, and as a result affect the vulnerability of groundwater. This paper researched the rainfall change trend in 50 years and analyzed its effect on the vulnerability of groundwater. At last the paper put forward some suggestions about the land use plan and the water resource protection.Firstly, it researched the climate change in 50 years based on the date of 34 stations and the GIS method, found the spatial and time-series trends of rainfall in Chongqing, and got the abrupt years by M-K method. Secondly, based on the COP method and added the land use factor as improvement, combined the hydrogeology and the land use data in 1990,2000 and 2008 to evaluate the vulnerability in karst area in Chongqing to find the time-series chang and spatial distribution of vulnerability class in the 1980s, 1990s and 2000s. At last by assessing the vulnerability in abrupt year analyze the effect of the rainfall on vulnerability of underground water in details. The results are as follows:1) The rainfall from 1961-2010 had a slight downward trend. The trends in autumn had an obvious increasing trend. Space variation of rainfall decreased from East to West. And the rainfall in the northeast and southeast of Chongqing was much more than the rainfall in west and east districts of Chongqing. The results of M-K method showed that the point of abrupt year were the year of 1989,1998,2002 and 2006.2) From 1980s to the 2010s, the area of the high level vulnerability in Chongqing increased.The levels of karst aquifer vulnerability from high to low were southeast, northeast, east and west, and using 70 underground water chemical characteristics in rainy season of 2009 to verify the reasonableness of the assessment results.3) By the method of sensitivity analysis, it showed that the climate change may be the dominate factor in groundwater vulnerability in the karst area of Chongqing. Various factors affecting the vulnerability are obtained by linear regression of the regression equation:Y=0.676 X1+0.076 X2+0.046 X3-0.030X4+108.770,R2=0.781. Type Y represents vulnerability change area, the Xi represents rainfall change, X2 on represents construction land area change, the X3 represents land area change, X4 represent woodland area change.4) By analyzing the vulnerability assessment in abrupt years, showed that the rainfall change in space will have an effect on the different vulnerability level in space. The high strength, frequency and continued time of rainfall will affect the infiltration and the moving time of pollution material from surface to ungerground, so will affect the vulnerability of aquifer and cause the area of high vulnerability in karst area increasmg.