Abstract:The upper Yellow River Basin is the most important water conservation and runoff producing areas in the Yellow River Basin,which is of decisive significance to the water resources security,ecological environment and food security of the Yellow River Basin.In recent years,under the background of warm and humid climate in Northwest China,the climate,ecology,hydrology and other issues in the upper Yellow River Basin have attracted great attention.Based on satellite remote sensing data,grid fusion data and hydrological monitoring data,this paper analyzes the multi-scale variation characteristics of climate and its impact on ecological vegetation and runoff in the upper Yellow River Basin.Results are summarized as follows:(1) From 1980 to 2018,the warming and wetting trend in the upper Yellow River Basin presents a relatively consistent climate characteristics in the whole region.The temperature and precipitation increase rates are 0.023℃/a,1.09 mm/a respectively.However,there are obvious regional differences at the same time.The increasing trend of precipitation is the most obvious over the confluence area of Huangshui River Basin and central part of Gansu Province,and the increasing trend of temperature is the most obvious in the desert area of Ningxia and Nei Monggol.Since 2000,the precipitation in the whole upper Yellow River Basin has increased significantly.After 2000,the actual evapotranspiration increases significantly in the confluence and flow areas but decreases in the south of the source area.(2) The current warm and humid climate is conducive to vegetation growth in the upper Yellow River Basin,and the vegetation growth rate has reached 0.04/(10 a) in the confluence and source areas since 1999.From the long-term trend,the vegetation index in the source and confluence areas has a significant positive correlation with precipitation in the previous year,while the vegetation index in the flow area has a significant correlation with precipitation in the current year.Precipitation has obvious effect on vegetation improvement in the upper Yellow River Basin,while temperature has more complex effect on vegetation.Different vegetation types in different regions are the possible reasons for the differences of precipitation,temperature and evapotranspiration.(3) Affected by the climate and vegetation variations,the annual runoff of Tangnaihai and Lanzhou stations shows a decreasing trend from 1980 to 2018 but a significant increasing trend since 1998,and the increase rate of annual runoff of Lanzhou station is three times that of Tangnaihai station.The long-term trend shows that annual runoff has a significant positive correlation with precipitation at Tangnaihai station in the current year,and the correlation coefficients of annual runoff with annual precipitation and evapotranspiration at Lanzhou station in the current year are significantly lower than those at Tangnaihai station.From the perspective of interannual fluctuation (after detrend),precipitation is the most important factor determining annual runoff,and the influences of ecological vegetation,frozen soil degradation,water storage change and social activities on runoff should not be ignored.This study provides a reference for scientific response to ecological protection in the upper Yellow River Basin and the realization of high-quality development of the Yellow River Basin.