| Water service is a very important service of ecosystem services, which supports human life and economic development, while has been greatly changed by climate change and human activities. Loess Plateau is the region severely affected by limited water. So, this paper studies the dynamic changes of runoff and soil moisture and their causes.The study applied transition analysis and found stream flow in the Loess Plateau contributes 65% of the discharge of the middle reach of the Yellow River, but its landscape has been severely shaped by human activities. Stream flow in the Loess Plateau has continued to decrease since the 1960s, at an average rate of-0.93 mm per year (P< 0.001). The long term decrease in stream flow mainly occurred in three sub-periods with 1970,1981 and 1996 as the transition points between periods. Although precipitation was dominant in causing variations in stream flow both for the entire period of 1961-2009 and soon after recovery from disturbance, human regulation played a dominant role (P< 0.05) in creating the transition point that caused stream drying. Most importantly, the provisioning of fresh water to central cities in the middle reach of Yellow River as an ES was greatly altered following each anthropogenic transition year, causing 56% of the reduction in the availability of fresh water for human beings in the 2000s compared to the 1960s.,Soil moisture is very important for vegetation survival in the Loess Plateau, but it is always affected by climate change and human activities. The result of the transect survey showed soil moisture of farmland is the largest, followed by grassland, shrubs-land and woodland. In the climate zone, in order to maintain soil moisture and take full advantage of the ecological benefit of the "soil reservoir", the low-density and low water consumption woodland or wild grassland should be preferred as the main land use type. The relationship of transect soil moisture response for precipitation was not significant, and soil moisture differences in different depth of soil layer were not obvious. One can find the soil moistures in the slope of 0-5 degrees and 10-15 degrees were the highest, which was the result of surface runoff and infiltration. The lower slope had the largest soil moisture, while the middle slope was minimal.The applicability of AMSR-E/2 for the surface soil moisture dynamic in the Loess Plateau was studied. Their surface soil moisture products didn’t reflect real SM in size, but could capture the temporal dynamic of SSM, especially when PPT occurred. Mann-Kendall test found that during 2003-2010 surface soil moisture in the Loess Plateau tended to decline (-0.0019m3/m3.yr), and this decline mainly occurred in the growing season (-0.0028m3/m3-yr). To explain the phenomenon, vegetation, precipitation and temperature tends were analyzed and found the trends in precipitation and temperature were not significant. But vegetation was significantly increased in the period of the inter-annual and growing season, at an average annual rate of 0.0067 and 0.011 (NDVI), respectively. The overlaps between them and the region of significant reduction of the soil moisture in the period of the inter-annual and growing season were about 20% and 34%, respectively, which indicated vegetation was the reason for leading to a decline of soil moisture over Loess Plateau. Partial correlation analysis and overlay analysis showed the dominant factors affecting surface soil moisture were precipitation and vegetation, whose reasons were that precipitation is the only source of soil moisture in Loess Plateau and the Loess Plateau is the key area of the grain for green. Since precipitation cannot be regulated, so in order to sustainable development in the Loess Plateau ecosystem, it needs to manage its vegetation, and the Grain for Green project should make measures based on local conditions and the mechanism for its period evaluation needs to be established, which changes the continuing downward trend of surface soil moisture. |
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