Regional difference in runoff regimes and changes in the Yarlung Zangbo river basin
Abstract. An improved understanding of runoff regimes and flow changes in the Yarlung Zangbo (YZ) river basin in the southern Tibetan Plateau (TP) is crucial for water resources management. However, regional characteristics in runoff regimes and changes are not comprehensively investigated in the YZ mostly due to the lack of hydrometeorological observations. Here, we comprehensively investigated runoff regimes and changes across six sub-basins in the YZ for 1971–2020 with a particular focus on the comparison between the upstream of the Nuxia (NX) basin and the downstream NX-Pasighat (NX-BXK), based on a newly generated precipitation dataset and a well-validated model with streamflow, glacier mass and snow cover observations. Our results reveal that large regional differences in runoff regimes and changes exist in the YZ basin. Firstly, runoff generation is dominated by rainfall in the entire YZ, and glacier runoff plays more important role in annual total runoff (19 %) in the NX-BXK than other sub-basins. Secondly, annual runoff shows an increasing trend in the NX basin but a decreasing trend in the NX-BXK due to rain-induced runoff changes, resulting in a weak increasing trend (3.1 mm/10 yr) in the YZ basin. Thirdly, total runoff increases of 5 %–22 % in the NX but decreases of 3 %–20 % in the NX-BXK in all seasons in 1998–2020 relative to the period 1971–1997. Finally, the NX basin faces a considerably hazard from extreme flood, but the NX-BXK basin faces more severe hydrological droughts. Glacier runoff shows limited roles in mitigating water shortages caused by drought in dry seasons, but it intensifies the flood frequency and severity among the basins in wet season. Our study offers a basic framework for clarifying the runoff regimes and flow changes in the TP basins.
He Sun et al.
Status: open (until 09 Apr 2023)
- RC1: 'Comment on hess-2023-16', Anonymous Referee #1, 26 Mar 2023 reply
He Sun et al.
Daily precipitation data with 10km resolution in the upper Brahmaputra (Yarlung Zangbo River) Basin-V2 (1951-2020) https://doi.org/10.11888/Atmos.tpdc.272885
He Sun et al.
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This paper offers an hydrological modeling of the Yarlung Zangbo River (also named upper Brahmaputra), and five sub-basins, over a long period of time, by using the VIC- Glacier model forced by the ERA5 reanalysis data.
This work is a good contribution to the knowledge of hydro-systems in the Tibetan Plateau, in particular regarding the question of partitioning the rainfall and glacial melt contributions.
The scientific approach is good, with a rigorus description of input data and results. Sources of uncertainties are also described in the results section, which is good.
Number and quality of tables and figure is good, despite the accuray of legends needs to be improved.
Scientific significance: Fair
Scientific quality: Good
Presentation quality: Fair
My main remark stands on the description of the calibration process, and in particular the time periods. Degree-Day factor (DDF) and 6 parameters of the VIC model are calibrated. Please provide more information and syntetic explaination of the process. What are the intial ranges of tested parameters? What are the method/tool employed for the optimization process? Please add a table with this info.
Also, regarding the periods of time: Is the whole analysis performed over the calibration period? Is there any calibration/validation periods? Please make this clear. In table 2: several period of time are quoted. What are they used for? Glaciar coverage and observed runoff are not availaible over the same period, so which period is used for the calibration process?
A real clarification of this is needed.
l68: 0.3-0.4°C: over wich period?
l83: at a rate of 48.2m yr−1: over wich period?
l106: which may be due to
l150: annual precipitation increases from upstream (283 mm) to downstream (1465 mm): what do you mean?
l155 snow cover fraction (SCF) = annual mean or winter maximum coverage?
l186 (eq 1): give the reference/source for this equation
l211: please give calibration period and validation period
l231: what is figure S2?
l244: Snow cover is considered on average over the basin?
l452: Zhang et al 2013 applyed the same model?
Figure 2: please quote data source in the legend
Figure 3: 1971-1980 is the whole calibration period of the model?
Figure 5: 'The asterisk indicates 95% significance confidence level.': not clear. why is there a confidence interval for correlation coeficient? Please clarify
Figure 6: please quote data source in the legend. please clarify '95% significance confidence level'
table 1: please give reference/product for the precipitation and temperature data and for DFF, SCA and SCF values. Are they results from the calibration process?