[1] The headwater catchments of the Yellow River Basin are of great importance for the whole basin in terms of water resources, and streamflow from these catchments has decreased in the last decades. The concept of climate elasticity was used to assess the impacts of climate and land surface change on the streamflow. Results show that for the period 1960-2000 the elasticity of streamflow in relation to precipitation and potential evapotranspiration are 2.10 and À1.04, respectively, indicating that streamflow is more sensitive to precipitation than to potential evapotranspiration. However, land use change played a more important role than climate in reducing streamflow in the 1990s. It is estimated that land use change is responsible for more than 70% of the streamflow reduction in the 1990s, while climate change contributed to less than 30% of the reduction.The precipitation elasticity appears to have an inverse relationship with the runoff coefficient but a positive relationship with the aridity index, showing that the drier the catchment, the more sensitive the streamflow with respect to precipitation change.

[1] In many places around the world, panevaporation has been detected to decrease with the increase in temperature, which is known as the ''panevaporation paradox.'' An example of the paradox was found in the Haihe River Basin from 1957 to 2001. To explain the mechanism of the paradox, an approach to quantify the contributions of climate factors to the panevaporation trend has been proposed, in which the individual contribution was defined as the product of the partial derivative and slope of the trend for the concerned variables. Four variables, including temperature, wind speed, solar radiation, and vapor pressure, were selected based on the Penman-Monteith method to assess their individual contribution to the panevaporation trend. The results showed that an increase in temperature resulted in the increase of panevaporation, but this effect had been offset by an increase in vapor pressure and decrease in wind speed and solar radiation. Wind speed was the dominant factor contributing to panevaporation decreases in the Haihe River Basin.

Groundwater residence time is an important indicator of hydrological cycle and essential for water resources development and utilization. In this paper, groundwater residence time in non-flood season, flood season and water year has been determined from daily streamflow hydrograph of ten hydrological stations in Wudinghe River Basin located in the middle reaches of the Yellow River Basin. Results have showed that: baseflow recession constant in Wudinghe River Basin ranges from 0.72 to 0.94 with a larger recession rate in flood season than that in non-flood season. Spatially, the recession rate of baseflow in loess area is the biggest, but is the smallest in the sandy area. The half-residence time of groundwater varies from 1.8 to 45.5 days while overall residence time of groundwater is between 34 and 342 days in different sub-basins of the Wudinghe River Basin. The annual average overall residence time of groundwater decreases from 117 days in the upper reaches to 73 days in the lower reaches.