Climate change dominated runoff change in the eastern Tibetan Plateau

Quantitatively identifying the impact of climatic and underlying surface condition changes on runoff is crucial for the efficient utilization of water resources and understanding hydroclimatic variability processes. This study aims to employ both Grid-RCCC-WBM model and Fu's equation based on Budyko hypothesis to quantitatively analyze the spatial patterns of runoff changes, driving forces, and upstream-downstream relationships in ten typical basins across the eastern Qinghai-Tibet Plateau (QTP) for the first time. Breaks for Additive Season and Trend method was used to detect breakpoints in runoff series and both hydrological model and Budyko equation categorized driving forces of runoff change into change in climatic (including precipitation and potential evaporation) and underlying surface conditions. The results indicated (i) significant abrupt changes in the runoff time series around 1998, with runoff increasing in all basins except for the source region of the Yellow River. (ii) significant upstream-downstream differences in the trend and magnitude of runoff changes between breakpoints in the Yangtze and Lancang Rivers over the past 20 years, and (iii) significant runoff response to climate variability after the breakpoints in the source region of the Yangtze and Yellow river. Our findings revealed that, contrary to the backdrop of decreasing precipitation, the upstream basins maintained increasing runoff relying on permafrost and glacier meltwater, while the downstream basins exhibited decreasing trend. The differences in runoff changes after the detected breakpoints were dominated by changes in underlying surface conditions, with the highest contribution rates observed in the Dajin (494 %), Lanzhou (398%), and Tangnaihai (197%) basins. This study involved both spatial pattern and upstream-downstream relationship of runoff change that can be widely applied to other large-scale regions and especially holds important implications for the scientific and rational utilization of water resources in the QTP.