Study On The Water Body And Vegetation Changes Of Large Lakes And Reservoirs In The Yellow River Mainstream Based On RS

In order to properly allocate, utilize and protect water resources of the Yellow River, our nation has constructed many water conservancy projects in the Yellow River Basin. So it is of great significance to study the water body and vegetation changes of large lakes and reservoirs in the Yellow River Mainstream.With the purpose of study, 3 lakes and 3 reservoirs on the Yellow River Mainstream(Gyaring Lake, Ngoring Lake, Longyangxia Reservoir, Liujiaxia Reservoir on the upstream, Xiaolangdi Reservoir on the midstream and Dongping Lake on the downstream) are selected as the study area. And the Landsat images of normal period(from 1987 to 2001) and water-sediment regulation(from 2002 to 2014) are selected together with the daily temperature and precipitation data collected by 107 stations in the Yellow River Basin from 1980 to 2015. Based on these data, the regulations of climate in recent 30 years in the Yellow River Basin are studied using RS technology and the spatial analysis tools of ArcGIS. The area of six selected water bodies and their surrounding vegetation condition are monitored dynamically by synthetically using improved normalized water index method, single band threshold value method and visual interpretation method, and the correlation of the changes of the area of water bodies and vegetation condition is studied combining the climate data in the area. Results are as follows:(1) The annual mean temperature generally showed an increasing trend in recent 30 years, rising from 6.965°C to 7.799°C, while the annual precipitation showed the trend of increase firstly and then decline, dropping from 437 mm to 426 mm and going up to 451 mm finally. The changes of annual temperature and precipitation in each selected water body had generally the same pattern with the entire Yellow River basin, though their patterns were slightly different from each other. The precipitation concentration degree(PCD) and precipitation concentration period(PCP) in Ngoring Lake and Gyaring Lake area were both on the rising trend, while in the other four areas, both the PCD and PCP were on the stable fluctuation path.(2) The area of water bodies of the Ngoring Lake showed a changing process of four phases. Stable phase(The area of water body was around 620 km2 from 1987 to 2002)- Shrinking phase(The area of water body reached the minimum of 606.8km2 in 2003) – Expanding phase(The area of water body of the Ngoring Lake showed sustained growth from 2003 to 2012, and was around 691.2km2 in 2012)- Decline phase(From 2012 to 2014, the area of water body decreased to 660 km2). The trend of the Gyaring Lake was similar to the Ngoring Lake, but a little bit slight. The area of water body of the Longyangxia Reservoir generally showed a fluctuating increasing trend(It increased from 184.1km2 in 1987, to 337.2 km2 in 2014, and that 386.9 km2 in 2012 was the maximum). The area of water body of the Liujiaxia Reservoir generally showed a fluctuating change(The maximum was 124.5km2 in 1995, the minimum was 81km2 in 2001), the area of water body of the Xiaolangdi Reservoir generally showed a fluctuating trend(It was around 180 km2, between 130.6km2 and 212.2km2). The area of water body of the Dongping Lake generally showed a changing process of three phases. Great fluctuations phase(Variation ratio was over 69.5%)- Slight fluctuations phase(It was around 140km2 from 1994 to 2001, the maximum annual variation ratio was 15.6%)- Relatively stable phase(It was around 145 km2 from 2004 to 2014).(3) The NDVI in areas of Ngoring Lake, Gyaring Lake Longyangxia Reservoir and Liujiaxia Reservoir was generally in a fluctuating growth trend, the mean NDVI in the area of Xiaolangdi Reservoir fluctuated significantly.(4) On the upstream of Yellow River, the area of water bodies of the Ngoring Lake, Gyaring Lake and Longyangxia Reservoir showed a relatively high correlation with their surrounding temperature, and the correlation index range from 0.515 to 0.784, this indicates that temperature has great influence on the area of water bodies on the upstream of Yellow River. The water body areas of Xiaolangdi Reservoir on the midstream and Dongping Lake on the downstream showed high correlation with the precipitation during the period of recent three months before the acquisition date of each image, the correlation coefficient reached 0.735 and 0.687 respectively, which were higher that the correlation coefficient between their water body areas and annual temperature. There are high correlations between the annual temperature and NDVI in the surrounding areas of each selected water body, with a minimum correlation coefficient of 0.51, while the correlations between NDVI and annual precipitation in each area are subtle.