| Qinghai Lake basin is located in the northeast of the Qinghai Tibet Plateau, the whole basin is located in the transition zone of the western arid region, the eastern monsoon region and the Qinghai Tibet plateau region. Under the background of globalization, the ecological environment of the Qinghai Lake basin is very sensitive and fragile, and the ecological status is very prominent. In recent 10 years, the ecological environment of the river basin has been improved, the Qinghai Lake area has been continuous growth for recent 15 years. So what caused the improvement of the ecological environment of the Qinghai Lake basin dominated by grassland and lakes, whether these changes are sustainable?Based on the analysis of the characteristics of climate change in recent 55 years in Qinghai Lake Basin, combined with ground observation data of grassland and lakes, this paper studied the dynamic changes of grassland vegetation phenological period in Qinghai Lake Basin, using remote sensing and GIS technology, comprehensively analyzed the temporal and spatial dynamics of above ground biomass and vegetation cover, and their relationships with the meteorological factorsin for 14 years(2002-2015), and then analyzed the dynamic change rule of the water level of Qinghai Lake and response to climate change, and using multi-source satellite data studied the changing characteristics of the Qinghai Lake water level, area and shorelines. Then we analyzed the driving force factors of grassland and lakes change, finally put forward the problem existed in Qinghai Lake Basin grassland and lakes research, as well as the focus of future research and the prospect to solve the scientific problems. The main conclusions are as follows:1) In the past 55 years, the climate of the Qinghai Lake basin had warm and wet trend, the annual average temperature, maximum temperature and minimum temperature and the average temperature, maximum temperature, minimum temperature in spring, summer, autumn and winter seasons showed an increasing trend, which annual average temperature and annual maximum temperature was significantly increased, the maximum temperature and minimum temperature in summer and autumn was significantly increased; the yearly precipitation and seasonal precipitation showed increasing trend, but spring precipitation increased not significantly. Seasonal precipitation increased from small to large as follows: winter > spring > autumn > summer; river runoff in spring, summer and autumn showed a trend of increasing, but no obvious change in winter; overall, annual sunshine hours showed a decreasing tendency, with a reduction rate of 17h/10a; annual average wind speed had significantly reducing trend, with a reducing speed of 0.14m/s/10 a and seasonal mean wind speed showed a significant decreasing trend.2) The grass turning green stage to the east coast of the Qinghai Lake in Haiyan County was significantly earlier than that of Gangcha county and northwest of Tianjun county. The grass withering period in Haiyan county maintained a normal level, it showed a trend of delay in Gangcha and Tianjun counties; days of forage growth in Gangcha and Tianjun was shortened, growth days was extended in Haiyan; the grassland vegetation growth condition in Qinghai Lake Basin presented a trend of improvement. In 2008 the grassland growth was the worst, and it was the best in 2012; based on the aboveground biomass of the ground observation and remote sensing monitoring results, the level of grassland biomass in Qinghai Lake basin was between 3000-6000 kg/hm2; remote sensing monitoring results showed that the low coverage grassland area in the Qinghai Lake basin decreased slowly in the past 13 years(2003-2015), the middle coverage of grassland area had a rapid increasing trend, the high coverage grassland fluctuated increase; correlation analysis of grassland biomass and temperature and precipitation showed that grassland biomass was positively correlated with temperature, there is a lag in temperature; under the condition of the growth needs, the precipitation can well promote the increase of biomass; using moving average method to evaluate grassland degradation, the results showed that after 2009 the trend of grassland degradation was suppressed, the ecological environment was improved; dune height and the horizontal moving distance in Haiyan county was increasing, and the moving distance of the sand dune was more significant than that of the height.3) Over the past 57 years(1959-2015), the water level of Qinghai Lake interannual variation showed a significant downward trend, water level decline rate was 0.52m/10 a, the interannual and monthly variation of water level had similar trend, but the interannual variation from January to May was not obvious, the water level interannual variation of from June to December tended to be significant; there was a significant positive correlation between the water level of Qinghai Lake lifting and precipitation and runoff into the lake, and the correlation with the runoff into the lake is greater than that of precipitation, and significant correlation analysis showed that the key factors of water level change was the temperature and evaporation.4) Over the past 50 years(1957-2010), the Qinghai Lake area had an overall downward trend, with a basic agreement with the change trend of water level, in the dry and wet seasons of nearly 15 years(2001-2015), the lake area was first decrease and then increase, since the beginning of 2005, the Qinghai Lake area and water level showed a consistent increase trend. The water area in wet season increased more significantly than that in dry season; environmental mitigation satellite can more precisely reflect the monthly, seasonal and interannual variations of Qinghai Lake areaand shoreline changes; remote sensing monitoring of the shoreline using TM and the Environmental Mitigation Satellite showed that over the past 50 years the shoreline changes of Qinghai lake varied greatly from north to south. The outlet from Quanji River to Shaliu River and the nearby areas of Shadao Lake and Haiyan Bay in the northwest of Qinghai Lake, the shoreline retreat was the most obvious.5) There are certain coupling relationship between meadows and lakes change of Qinghai Lake basin, but also differences; Qinghai lake level decline caused mainly due to climate change, although the human factors of Qinghai Lake Basin Grassland and influential position, but not the dominant factor lifting or declining of Qinghai Lake. |
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