Co-evolving mechanisms of climate - vegetation - hydrology in the source region of Yellow River

As if a tower to supply water downstream, the change pattern of water yield of the head water of the Yellow River has drawn high attention of all societal sectors, but not very clear due to the tangling influences by many factors.   Based on the multi-sources of vegetation, hydro-meteorological information, the Vegetation Interface Processes eco-hydrological dynamic model is used to investigate the evolving processes of eco-hydrological elements in the Yellow River basin upon Tangnaihai gauge from 2000 to 2019.  Results showed that the catchment is facing a warming and wetting climate in past two decades, the vegetation growing condition improved quite a lot with the growing period extending for more than 10 days. There has been more glaciers melting in summer and lakes water extension, along with gently increasing of soil moisture. Water yield capacity in the basin has decreased, especially in autumn. Vegetation evapotranspiration (ET) and gross primary productivity (GPP) showed significant synergetic relationship with co-variation. Both ET and GPP exhibited significant increase, in which the top rates occurred in the altitude between 3000 to 4000 m. Water use efficiency (WUE) is enhancing. Attribute analysis showed that the increasing precipitation, vapor pressure deficit and solar radiation were the dominated factors to intensify water-vapor exchange between land surface and atmosphere. Obviously, the warm-wet tendency of climate in the basin apparently improved the ecological environment. However, the increased ecological water consumption resulting in decreased capacity of water yield which impacts adversely the blue water supply, particularly under future climate change.  Trade-off policy action is needed with the aid of elucidating the evolving mechanisms of hydrological and vegetation dynamics to provide scientific basis to maintain the ecosystem sustainability and functioning.