The LUCC and spatio-temporal variability of climate and their impacts on streamflow in the eco- environment source region of the yellow river

As the eco-environment source region of the Yellow River, Qinghai-Tibet plateau is the startup region of climate change in China and it\´s very sensitive to climate change. The streamflow in this study region decrease sharply since the mid- 1980s. The streamflow shows least cycle of 5-10 years by analyzing the streamflow data in 40 years of three gauging stations (Maduo, Jimai and Tangnaihai) based on the plural Morlet wavelet analysis. The meteorological and streamflow data from 1986 to 2000 were separated into three periods, to obtain the 5 years\´ average data, and then the trend and cycle of the change are analyzed. The streamflow of the three stations in three periods decrease sharply compare to the average streamflow in the past 40 years, and the decreasing velocity of streamflow was increasing in recent years; especially in the Maduo gauging station, the average streamflow decrease 80% compare to the averaging streamflow in the past 40 year; the velocity of streamflow decrease from September to March in the next year is bigger than that from April to August. But the precipitation do not decrease in the three periods of three station; the daily minimum temperature increase 0.5deg, the daily maximum temperature also increase with less range; the change of surface water evaporation is irregular, which increase in the first two periods and decreased in the last period in Maduo station, while the Jimai station has opposite situation. Based on filed investigation and comparison of two periods of remote sensing data obtained in 1986 and 2000, from spatial distribution pattern variations and type transformation trend, the spatial changes and evolution pattern of land ecosystem in the eco-environment source regions of the Yellow river were analyzed using the analytical method of landscape ecological spatial pattern, the environment changed acutely. The high coveralpine cold steppe, medical cover alpine clod steppe, high cover alpine cold meadow, medial cover alpine co- ld meadow, swamp meadow, alpine cold swamp meadow decrease 19.35%, 24.96%, 3.32%, 9.82%, 13.08%, 40.82%, respectively; river, lake and glacier decrease 11.35%, 4.90%, 29.26%, respectively; low cover alpine cold steppe, low cover alpine cold meadow and desertification land increase 36.27 % , 3.25 % , 10.86 % , respectively. The SWAT (soil and water assessment tools) model is employed in this study, the meteorological data were obtained through "Gradient plus Inverse-Distance-Squared" (GIDS) based on the 23 weather stations in or near the study area in recent 15 years, vegetation types were derived based on the two periods of remote sensing data, the required soil parameter is obtained from the soil classification and soil texture database at the scale of 1:1,000,000. The streamflow which simulated by the SWAT model match the observed data quite well, the Nash parameter of monthly and yearly modeled streamflow in the periods of calibration and validation all exceed 0.8. After simulating the streamflow and evapotranspiration under different climate and land use scenarios, this paper try to find the impacts of climate change and LUCC on the streamflow.