Abstract: Runoff generation and its dynamics are the fundamental of hydrology and are very crucial to water resource management. Based on isotope hydrograph method, the paper explored and compared the runoff generation mechanism of two typical inland rivers in the Tianshan Mountains (i.e., Urumqi River on the north slope and Huangshuigou River on the south slope), based on the monitored weather, flow and isotope data of a hydrological year. Results show as follows: (1) in both rivers, precipitation, river water and groundwater exhibit noticeable spatial and temporal variations in stable δ¹⁸O and δD compositions, and there is an increasing trend of δ¹⁸O in the river water during snowmelt period (late autumn and spring); (2) isotope hydrograph separation shows that generally, groundwater is the major recharging source (over 50% of streamflow), followed by glaciermelt, snowmelt and precipitation in these two rivers; Urumqi River has a larger contribution from glaciermelt than Huangshuigou River does, indicating that Urumqi River is more sensitive to the temperature change; (3) these two rivers have similar contribution components in all seasons except for spring in which Huangshuigou River has similar contributions from groundwater and snowmelt, while Urumqi River has a larger contribution from groundwater than snowmelt.

Key words: Isotopic separation, Streamflow component, Urumqi River Basin, Huangshuigou River Basin