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Appropriate allocation of limited freshwater resources to humans and ecosystems is an important issue hampering sustainable development in mountainous regions. The Taihang Mountain Region (TMR), including the Yellow and Hai river basins, is an important water source area for the North China Plain. The distributed hydrological model Water and Energy transfer Processes in Large river basins (WEP-L) was used to simulate the water cycle processes and to summarize the temporal and spatial changes in the blue and green water in the TMR from 1956 to 2015. The results show that in the period 2011–2015 the annual average blue water decreased by 7.31 × 109 m3, while the annual average green water increased by 13.60 × 109 m3 compared to 1956–1960. At the inter-annual time scale, the blue water exhibited a downward trend while the green water exhibited an upward trend. The amount of seasonal blue water in the TMR is ranked in descending order: summer, autumn, spring and winter, while for green water, the rank is summer, spring, autumn and winter. The amounts of blue and green water are higher on the windward than on the leeward slopes. The blue water yield is generally higher in forests and grasslands than in farmland, while the green water exhibits the opposite response. A greater emphasis should be placed on the widening gap between blue water and green water due to climate warming, and on soil and water conservation measures. [ABSTRACT FROM AUTHOR]

Distribution of residence time has been commonly used to characterize the responsecatchment runoff processes. Most previous studies on water residence time have been mainlyfocused on large scale analysis in time and space and on estimating residence timedistribution of total runoff. In this study, we analyzed residence time distribution (RTD) ofdifferent runoff components at event scale in Hydrohill experimental catchment, which islocated in Chuzhou City, Anhui Province, China. Hydrochemical and isotopic data, i.e., 18O,D, anions (HCO3−, Cl−, NO3−, SO42− and F−), cations (K+, Na+, Ca2+ and Mg2+) anddissolved Si in water samples were collected during the rainfall events in 2016, which areused to characterize the response of different runoff components by combining lumpedparameter models. Results showed that 18O and Cl− are the most suitable indicators toevaluate RTD of runoff components. On the experimental catchment scale, groundwaterrunoff gets the longest residence rime among all three runoff components. Residencerime of interflow runoff is approximately 1.38 times longer than that of surfacerunoff. Hydro-chemical tracing provide an effective way to easily measure andunderstanding hydrological processes for critical zone, which could support hydrologicalmodel development by strengthening physical base of hydrological cycle. However,what caused difference in residence time of runoff components and how to quantifyinteraction between different runoff components should be enhanced in furtherstudy. Key words: water residence time; runoff components; lumped parameter models;hydro-chemical and isotopic data; Hydrohill experimental catchment Acknowledgements: The work has been supported by National Natural ScienceFoundation of China (Grant No. 41830863) and National Key Research and DevelopmentPrograms of China (Grant No. 2016YFA0601501) [ABSTRACT FROM AUTHOR]